Computer-DAC
 

I've connected a Cambridge Dacmagic to a Mac Mini via the optical
connection, and I'm not sure which settings to select in the Apple audio
setup, for stereo playback through iTunes. It offers a variety of 2ch
settings with a variety of formats (44.1 - 96) and bits (16 - 24). They
all work, but I'd like the theoretical best setting, if there is one.

Thanks, Rob

Computer-DAC
 

On 08/02/2010 16:50, Rob wrote:
I've connected a Cambridge Dacmagic to a Mac Mini via the optical
connection, and I'm not sure which settings to select in the Apple audio
setup, for stereo playback through iTunes. It offers a variety of 2ch
settings with a variety of formats (44.1 - 96) and bits (16 - 24). They
all work, but I'd like the theoretical best setting, if there is one.

Whatever suits the bit rate and depth that is common between the
majority of media files played back. 16bit / 44.1kHz for things sourced
from CD (even as an iTunes download)

Though what happens if you replay audio snatched from a DVD? If you are
met with silence, you may have to occasionally reset output to 48kHz,
and remember to set it back afterwards - or just leave it at 48kHz and
hope that the internal circuits do a decent job of 44.1/48 resampling.

Only your ears can tell ...

--
Adrian C

Computer-DAC
 

"Rob" wrote in message
m
I've connected a Cambridge Dacmagic to a Mac Mini via the
optical connection, and I'm not sure which settings to
select in the Apple audio setup, for stereo playback
through iTunes. It offers a variety of 2ch settings with
a variety of formats (44.1 - 96) and bits (16 - 24). They
all work, but I'd like the theoretical best setting, if
there is one.

This depends on the media you are playing. Media plays best in the format
it was recorded at.

If the files you play are MP3 and MP4 and the like, 44.1 / 16 is what you
want.

Computer-DAC
 

On 08/02/2010 19:04, Adrian C wrote:
On 08/02/2010 16:50, Rob wrote:
I've connected a Cambridge Dacmagic to a Mac Mini via the optical
connection, and I'm not sure which settings to select in the Apple audio
setup, for stereo playback through iTunes. It offers a variety of 2ch
settings with a variety of formats (44.1 - 96) and bits (16 - 24). They
all work, but I'd like the theoretical best setting, if there is one.

Whatever suits the bit rate and depth that is common between the
majority of media files played back. 16bit / 44.1kHz for things sourced
from CD (even as an iTunes download)


I've not knowingly recorded anything at anything else. That's not to say
there's nothing else there of course.


Though what happens if you replay audio snatched from a DVD? If you are
met with silence, you may have to occasionally reset output to 48kHz,
and remember to set it back afterwards - or just leave it at 48kHz and
hope that the internal circuits do a decent job of 44.1/48 resampling.


Yes, (but) I think iTunes sorts all that sort of thing out.

Only your ears can tell ...


I doubt it! Although I have to say it does sound pretty good, at least
compared to what went before.

Computer-DAC
 

In article , Rob
wrote:
On 08/02/2010 19:04, Adrian C wrote:
On 08/02/2010 16:50, Rob wrote:
I've connected a Cambridge Dacmagic to a Mac Mini via the optical
connection, and I'm not sure which settings to select in the Apple
audio setup, for stereo playback through iTunes. It offers a variety
of 2ch settings with a variety of formats (44.1 - 96) and bits (16 -
24). They all work, but I'd like the theoretical best setting, if
there is one.

The 'theoretical best' would be for the rate to always match that of the
source material. Not to have one rate regardless of source.


Whatever suits the bit rate and depth that is common between the
majority of media files played back. 16bit / 44.1kHz for things
sourced from CD (even as an iTunes download)


I've not knowingly recorded anything at anything else. That's not to say
there's nothing else there of course.

An advantage of the DACMagic is that it has a set of LEDs that show you
what sampling rate it is receiving. So the basic check is to play files
whose sample rate you know and look to make sure the correct LED comes on.
So if you play a CD Audio file or the BBC iPlayer the '44k' LED should be
lit, but if playing an LPCM DVD Video then the '48k' (or higher if lucky)
one should light.

Don't know what software you have as I don't take much interest in Macs.
However I'd hope your playing software will tell you the sample rate of the
file being played.


Though what happens if you replay audio snatched from a DVD? If you
are met with silence, you may have to occasionally reset output to
48kHz, and remember to set it back afterwards - or just leave it at
48kHz and hope that the internal circuits do a decent job of 44.1/48
resampling.


Yes, (but) I think iTunes sorts all that sort of thing out.

The DACMagic LEDs will tell you if the rate being output matches the source
material or not.

What that *can't* tell you is if the output is 'bit perfect' or not. To do
that you need to record the output sample stream and compare it with the
source. Again, since I don't know much about the Macs I can't say. However
you could try asking Cambridge Audio.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Computer-DAC
 

On 09/02/2010 09:29, Jim Lesurf wrote:
In a.com, Rob
wrote:
On 08/02/2010 19:04, Adrian C wrote:
On 08/02/2010 16:50, Rob wrote:
I've connected a Cambridge Dacmagic to a Mac Mini via the optical
connection, and I'm not sure which settings to select in the Apple
audio setup, for stereo playback through iTunes. It offers a variety
of 2ch settings with a variety of formats (44.1 - 96) and bits (16 -
24). They all work, but I'd like the theoretical best setting, if
there is one.

The 'theoretical best' would be for the rate to always match that of the
source material. Not to have one rate regardless of source.


OK, thanks. I was thrown by the fact that the DAC seems to take a signal
and upsample, regardless.


Whatever suits the bit rate and depth that is common between the
majority of media files played back. 16bit / 44.1kHz for things
sourced from CD (even as an iTunes download)


I've not knowingly recorded anything at anything else. That's not to say
there's nothing else there of course.

An advantage of the DACMagic is that it has a set of LEDs that show you
what sampling rate it is receiving. So the basic check is to play files
whose sample rate you know and look to make sure the correct LED comes on.
So if you play a CD Audio file or the BBC iPlayer the '44k' LED should be
lit, but if playing an LPCM DVD Video then the '48k' (or higher if lucky)
one should light.


Indeed it does.

Don't know what software you have as I don't take much interest in Macs.

No, that's fine, and FYI it's called 'iTunes'.


However I'd hope your playing software will tell you the sample rate of the
file being played.


It does, yes.


Though what happens if you replay audio snatched from a DVD? If you
are met with silence, you may have to occasionally reset output to
48kHz, and remember to set it back afterwards - or just leave it at
48kHz and hope that the internal circuits do a decent job of 44.1/48
resampling.


Yes, (but) I think iTunes sorts all that sort of thing out.

The DACMagic LEDs will tell you if the rate being output matches the source
material or not.


And . . . it depends. iTunes tends to sample up/down to 44.1,
regardless. I say 'tend' - if I use another application, Plex, for music
replay it changes system settings to 48/16 as if by magic - just FYI as
an example of the carnival going on behind the scenes. I can't find any
Mac software that will output the file in the recorded format.

The output depends on the system settings, which will not respond to the
audio file's format, and the applications software (iTunes, etc).

What that *can't* tell you is if the output is 'bit perfect' or not. To do
that you need to record the output sample stream and compare it with the
source.


Again, since I don't know much about the Macs I can't say.

Yes, I see.

However
you could try asking Cambridge Audio.


There's a fair bit on t'internet, and it seems to make a pretty good job
of things using the correct settings, but apparently the USB interface
isn't up to much - sounded fine to me, have to say.

http://www.stereophile.com/digitalpr...r/index2.html#

Rob

Computer-DAC
 

On 08/02/2010 19:17, Arny Krueger wrote:
wrote in message
m
I've connected a Cambridge Dacmagic to a Mac Mini via the
optical connection, and I'm not sure which settings to
select in the Apple audio setup, for stereo playback
through iTunes. It offers a variety of 2ch settings with
a variety of formats (44.1 - 96) and bits (16 - 24). They
all work, but I'd like the theoretical best setting, if
there is one.

This depends on the media you are playing. Media plays best in the format
it was recorded at.

If the files you play are MP3 and MP4 and the like, 44.1 / 16 is what you
want.


Yep, thanks. As you might gather from another reply, it's a little
difficult following which software does what.

Rob

Computer-DAC
 

"Rob" wrote


No, that's fine, and FYI it's called 'iTunes'.


Hi Rob - my Mac Mini died suddenly after only two weeks!

Gone and refunded* now, I don't think I'll go that route again - there are
some very pleasant aspect to the Mac system, but from what little I saw and
remember of it, 'iTunes' was the least appealing thing on it! I know you
could resist without too much of a struggle, but it seemed to want to take
me 'shopping' every time I looked at it!


*After a phone call from me to collect the £21.07 they knocked off the
refund for no reason other than it was (is?) obviously worth trying it on!

Computer-DAC
 

Rob wrote:

On 08/02/2010 19:17, Arny Krueger wrote:
wrote in message
m
I've connected a Cambridge Dacmagic to a Mac Mini via the optical
connection, and I'm not sure which settings to select in the Apple
audio setup, for stereo playback through iTunes. It offers a variety
of 2ch settings with a variety of formats (44.1 - 96) and bits (16 -
24). They all work, but I'd like the theoretical best setting, if
there is one.

This depends on the media you are playing. Media plays best in the
format it was recorded at.

If the files you play are MP3 and MP4 and the like, 44.1 / 16 is what
you want.


Yep, thanks. As you might gather from another reply, it's a little
difficult following which software does what.

It is a tricky subject.

What would be best is "bit perfect', what comes out is what went in
unchanged in any way, this is something more than something simply coming
out at the same sampling rate.

Foobar2000, with a plugin, did just that here on Vista, foobar2000 takes
sole control of the output card bypassing the digital mixer which is the bit
that "messes" things up. (Being Vista it could not play MP3s without
glitches so despite being bit perfect it was in fact useless.) The rationale
from Microsoft was along the lines that their software manipulation of the
data was so very clever that bit rate conversion was just fine.

I now use a Mac mini, which may be no more inherently 'bit perfect' than
Windows, there is still a mixer in there to add in computer bleeps etc.,
obviously those are all turned off but the mixer will still be there but
with one input mute.

To duck the bitrate issue I use the analogue output from the Mac mini which
sounds very good to me. The thought does occur that the sound is going
through that digital mixer anyway so what I am listening to is not 'bit
perfect' after all.

I did say it is tricky.

Anyway while googling and failing to find any actual facts, just look at
this :-

http://www.computeraudiophile.com/co...ct-digital-out

"It is well known that any lossless use will not sound as good as a flat PCM
file like AIFF or WAV." and "Just in the same way that FLAC does not sound
as good as WAV on a PC.", by one J Gordon Rankin.

Surely that is just crap, at least I hope it is.

--
David Pitt

Computer-DAC
 

In article , Rob
wrote:
On 09/02/2010 09:29, Jim Lesurf wrote:
In a.com, Rob



Though what happens if you replay audio snatched from a DVD? If you
are met with silence, you may have to occasionally reset output to
48kHz, and remember to set it back afterwards - or just leave it at
48kHz and hope that the internal circuits do a decent job of 44.1/48
resampling.


Yes, (but) I think iTunes sorts all that sort of thing out.

The DACMagic LEDs will tell you if the rate being output matches the
source material or not.


And . . . it depends. iTunes tends to sample up/down to 44.1,
regardless. I say 'tend' - if I use another application, Plex, for music
replay it changes system settings to 48/16 as if by magic - just FYI as
an example of the carnival going on behind the scenes. I can't find any
Mac software that will output the file in the recorded format.

IIUC the above shows that the Mac hardware is quite capable of providing
both 44.1 and 48. If so, your main 'challenge' (as managers say) is to find
software that simply passes out the data at the correct rates in every
case. Afraid I can't say anything about that with the Mac as I know little
about Mac software.

If I get a chance I'll ask a colleague who is a Mac user to see if he
knows. However my impression is that many computer users have zero
awareness of this issue and blindly assume that if they can hear sound it
must be "working OK". They then blame any nasty noises on the source
material.


However you could try asking Cambridge Audio.


There's a fair bit on t'internet, and it seems to make a pretty good job
of things using the correct settings, but apparently the USB interface
isn't up to much - sounded fine to me, have to say.

http://www.stereophile.com/digitalpr...r/index2.html#

Not yet looked at the above link. However I do get Stereophile on
subscription and remember reading the DACmagic review (and a later addition
to it IIRC). My impression is that operation with the USB will depend on
how evenly the computer sends the data. If so the real problem is initially
down to that.

FWIW When I started using my DACMagic i fed it from the computer via USB
and then ran an optical output from the DACMagic to my Meridian 563 DAC for
the actual conversion. In effect just using the DACMagic as a USB-SPDIF
convertor, and then having the Meridian reclocking the data to suppress any
jitter.

However I also experimented with using the DACMagic without the Meridian
and eventually decided that also sounded fine. Decided it sounded
indistinguishable to me. So I now just use the DACMagic and am moving the
Meridian on to other duties. Another advantage of this is that the DACMagic
can playback digital recordings at rates above 48k from my new HD P2.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Computer-DAC
 

In article , David Pitt
wrote:
Rob wrote:


Anyway while googling and failing to find any actual facts, just look at
this :-

http://www.computeraudiophile.com/co...ct-digital-out

"It is well known that any lossless use will not sound as good as a flat
PCM file like AIFF or WAV." and "Just in the same way that FLAC does not
sound as good as WAV on a PC.", by one J Gordon Rankin.

Surely that is just crap, at least I hope it is.

It is possible that some hardware/software combinations are struggling to
'keep up' and buffer out the data at a decently uniform rate. But that
should not be the case. My impression is that in 'computer land' there is
often a lack of real understanding, or even basic check measurements.

Indeed, an article I read in a Linux mag a few months ago by a 'sound
expert' made me wonder what kind of results you'd get if I'd understood
correctly what he seemed to be telling people to do! But then, what he
wrote did seem to be par for a music biz where level compression and
clipping seems to be regarded as 'normal' in more ways that one! :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Computer-DAC
 

Jim Lesurf wrote:
In article , Rob
wrote:
On 09/02/2010 09:29, Jim Lesurf wrote:
In a.com, Rob


Though what happens if you replay audio snatched from a DVD? If you
are met with silence, you may have to occasionally reset output to
48kHz, and remember to set it back afterwards - or just leave it at
48kHz and hope that the internal circuits do a decent job of 44.1/48
resampling.

Yes, (but) I think iTunes sorts all that sort of thing out.
The DACMagic LEDs will tell you if the rate being output matches the
source material or not.


And . . . it depends. iTunes tends to sample up/down to 44.1,
regardless. I say 'tend' - if I use another application, Plex, for music
replay it changes system settings to 48/16 as if by magic - just FYI as
an example of the carnival going on behind the scenes. I can't find any
Mac software that will output the file in the recorded format.

IIUC the above shows that the Mac hardware is quite capable of providing
both 44.1 and 48. If so, your main 'challenge' (as managers say)

Yeah, the last one that said that to me didn't realise how close to death he was. :)




--
Bill Coombes

Computer-DAC
 

On 09/02/2010 18:43, Keith G wrote:

"Rob" wrote


No, that's fine, and FYI it's called 'iTunes'.


Hi Rob - my Mac Mini died suddenly after only two weeks!

Gone and refunded* now, I don't think I'll go that route again - there
are some very pleasant aspect to the Mac system, but from what little I
saw and remember of it, 'iTunes' was the least appealing thing on it! I
know you could resist without too much of a struggle, but it seemed to
want to take me 'shopping' every time I looked at it!


Lightweight! At least you gave it a go. I can see why Macs are
infuriating/not worth the bother for many - they just hit the spot for
me in terms of productivity/engineering/reliability/ease-pleasure of use.

Computer-DAC
 

On 10/02/2010 09:22, Jim Lesurf wrote:
In a.com, Rob
wrote:
On 09/02/2010 09:29, Jim Lesurf wrote:
In a.com, Rob



Though what happens if you replay audio snatched from a DVD? If you
are met with silence, you may have to occasionally reset output to
48kHz, and remember to set it back afterwards - or just leave it at
48kHz and hope that the internal circuits do a decent job of 44.1/48
resampling.


Yes, (but) I think iTunes sorts all that sort of thing out.

The DACMagic LEDs will tell you if the rate being output matches the
source material or not.


And . . . it depends. iTunes tends to sample up/down to 44.1,
regardless. I say 'tend' - if I use another application, Plex, for music
replay it changes system settings to 48/16 as if by magic - just FYI as
an example of the carnival going on behind the scenes. I can't find any
Mac software that will output the file in the recorded format.

IIUC the above shows that the Mac hardware is quite capable of providing
both 44.1 and 48. If so, your main 'challenge' (as managers say) is to find
software that simply passes out the data at the correct rates in every
case. Afraid I can't say anything about that with the Mac as I know little
about Mac software.


Yes, the Mac will 'deal' with 32 - 96Khz. Thing is, there's an OS 'gate'
that controls input and output. It's called the Audio Midi Setup
application. Now, other apps can 'call' that app, and vary the sample
rate as per the source file. None that I can see do in a consistent way.

If I get a chance I'll ask a colleague who is a Mac user to see if he
knows. However my impression is that many computer users have zero
awareness of this issue and blindly assume that if they can hear sound it
must be "working OK". They then blame any nasty noises on the source
material.


That's kind, thanks. I've put a similar query on a Mac newsgroup, and
it's not something of interest it seems. I simply want it to 'work
right'. Which it does, I think, if I set the settings to match the
source file.


However you could try asking Cambridge Audio.


There's a fair bit on t'internet, and it seems to make a pretty good job
of things using the correct settings, but apparently the USB interface
isn't up to much - sounded fine to me, have to say.

http://www.stereophile.com/digitalpr...r/index2.html#

Not yet looked at the above link. However I do get Stereophile on
subscription and remember reading the DACmagic review (and a later addition
to it IIRC). My impression is that operation with the USB will depend on
how evenly the computer sends the data. If so the real problem is initially
down to that.

FWIW When I started using my DACMagic i fed it from the computer via USB
and then ran an optical output from the DACMagic to my Meridian 563 DAC for
the actual conversion. In effect just using the DACMagic as a USB-SPDIF
convertor, and then having the Meridian reclocking the data to suppress any
jitter.

However I also experimented with using the DACMagic without the Meridian
and eventually decided that also sounded fine. Decided it sounded
indistinguishable to me. So I now just use the DACMagic and am moving the
Meridian on to other duties. Another advantage of this is that the DACMagic
can playback digital recordings at rates above 48k from my new HD P2.


'Only' 16 bit via USB IIUC, but life goes on :-)

Computer-DAC
 

On 10/02/2010 09:00, David Pitt wrote:
wrote:

On 08/02/2010 19:17, Arny Krueger wrote:
wrote in message
m
I've connected a Cambridge Dacmagic to a Mac Mini via the optical
connection, and I'm not sure which settings to select in the Apple
audio setup, for stereo playback through iTunes. It offers a variety
of 2ch settings with a variety of formats (44.1 - 96) and bits (16 -
24). They all work, but I'd like the theoretical best setting, if
there is one.

This depends on the media you are playing. Media plays best in the
format it was recorded at.

If the files you play are MP3 and MP4 and the like, 44.1 / 16 is what
you want.


Yep, thanks. As you might gather from another reply, it's a little
difficult following which software does what.

It is a tricky subject.

What would be best is "bit perfect', what comes out is what went in
unchanged in any way, this is something more than something simply coming
out at the same sampling rate.

Foobar2000, with a plugin, did just that here on Vista, foobar2000 takes
sole control of the output card bypassing the digital mixer which is the bit
that "messes" things up. (Being Vista it could not play MP3s without
glitches so despite being bit perfect it was in fact useless.) The rationale
from Microsoft was along the lines that their software manipulation of the
data was so very clever that bit rate conversion was just fine.

I now use a Mac mini, which may be no more inherently 'bit perfect' than
Windows, there is still a mixer in there to add in computer bleeps etc.,
obviously those are all turned off but the mixer will still be there but
with one input mute.

To duck the bitrate issue I use the analogue output from the Mac mini which
sounds very good to me. The thought does occur that the sound is going
through that digital mixer anyway so what I am listening to is not 'bit
perfect' after all.


It could be new clothes syndrome, but I reckon this DAC sounds a fair
bit better than the analogue out.

I did say it is tricky.

Anyway while googling and failing to find any actual facts, just look at
this :-

http://www.computeraudiophile.com/co...ct-digital-out

"It is well known that any lossless use will not sound as good as a flat PCM
file like AIFF or WAV." and "Just in the same way that FLAC does not sound
as good as WAV on a PC.", by one J Gordon Rankin.

Surely that is just crap, at least I hope it is.


If your summary is a reflection (I couldn't wade through it all!) but
surely it's nonsense? Lossless compression and decompression has nothing
to do with sound - it's simply processing to/from the original form (wav
etc), in much the same way as zipped files are compressed/decompressed.
IIUC.

On bit perfect: do you/anyone know how it's measured/tested?

Also, I think I read that if the computer software volume control works,
the digital output is not bit perfect.

Rob

Computer-DAC
 

In article , Rob
wrote:
On 10/02/2010 09:22, Jim Lesurf wrote:

And . . . it depends. iTunes tends to sample up/down to 44.1,
regardless. I say 'tend' - if I use another application, Plex, for
music replay it changes system settings to 48/16 as if by magic -
just FYI as an example of the carnival going on behind the scenes. I
can't find any Mac software that will output the file in the recorded
format.

IIUC the above shows that the Mac hardware is quite capable of
providing both 44.1 and 48. If so, your main 'challenge' (as managers
say) is to find software that simply passes out the data at the
correct rates in every case. Afraid I can't say anything about that
with the Mac as I know little about Mac software.


Yes, the Mac will 'deal' with 32 - 96Khz. Thing is, there's an OS 'gate'
that controls input and output. It's called the Audio Midi Setup
application.

Curious that it has 'midi' in the name as that is something quite different
to dealing with standard LPCM data.

Now, other apps can 'call' that app, and vary the sample
rate as per the source file. None that I can see do in a consistent way.

If I get a chance I'll ask a colleague who is a Mac user to see if he
knows. However my impression is that many computer users have zero
awareness of this issue and blindly assume that if they can hear sound
it must be "working OK". They then blame any nasty noises on the
source material.


That's kind, thanks. I've put a similar query on a Mac newsgroup, and
it's not something of interest it seems.

That seems consistent with the impression I've had of the level of interest
and awareness of these matters amongst most Windows and Linux and RO
users. The default assumption people seem to make is that if they can 'hear
the music' then the sound system of the computer is 'working'. They then
blame any problems on the source material being poor, or some other reason.
No thought that you need to get the rate correct for the source and obtain
bit perfect output for LPCM. But then I guess most people will be using
mp3, etc, a lot of the time without having any idea how the compressed
formats differ from LPCM.



FWIW When I started using my DACMagic i fed it from the computer via
USB and then ran an optical output from the DACMagic to my Meridian
563 DAC for the actual conversion. In effect just using the DACMagic
as a USB-SPDIF convertor, and then having the Meridian reclocking the
data to suppress any jitter.

However I also experimented with using the DACMagic without the
Meridian and eventually decided that also sounded fine. Decided it
sounded indistinguishable to me. So I now just use the DACMagic and am
moving the Meridian on to other duties. Another advantage of this is
that the DACMagic can playback digital recordings at rates above 48k
from my new HD P2.


'Only' 16 bit via USB IIUC, but life goes on :-)

I've recently been experimenting with rates above 48k. But as yet I've
simply not bothered with 24 bit at all. Although there may be some
situations where I can see a use for it. Overall, though, I am currently
happy with 44k/16 *if* the source material is of good quality and carefully
reproduced.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Computer-DAC
 

In article , Rob
wrote:

On bit perfect: do you/anyone know how it's measured/tested?

I've been though this in recent months. e.g. for

http://www.audiomisc.co.uk/Linux/Sou...Computing.html

http://www.audiomisc.co.uk/Linux/Sou...stenAgain.html

The key is that you need to have a recorder that can accept the spdif (or
USB) output and record the sample stream. Then compare that with the LPCM
source you are playing on a sample-by-sample basis.

For 44k/16 I've used a Pioneer Audio CD recorder. But am changing to the
Tascam HD P2. One reason being that it can record other sample rates and 24
bit as well as 16.

I then use my own RO and ROX/Linux apps to examine the results. I will be
making copies of the software available in due course so anyone who wishes
can use them. But the key point is to have the ability to record what
emerges from the computer.


Also, I think I read that if the computer software volume control works,
the digital output is not bit perfect.

Yes. It is necessary to set any such control to '0dB' or '100 percent'.
....and also necessary to check that this *does* mean 'gain of unity
applied'. I've encountered cases where 'volume' controls do *not* leave the
data values unchanged for such a setting! I'm afraid that the situation
with computer sound seems a right guddle to me. It seems to be aimed at
assuming ignorant users will have no interest in audio quality. :-/

BTW as you can see from the above webpages you need to set '11' on the BBC
iPlayer to stop the iPlayer software from altering the output level. i.e it
uses the 'Spinal Tap' scale. 8-}

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Computer-DAC
 

Jim Lesurf wrote:

In article , Rob
wrote:
On 10/02/2010 09:22, Jim Lesurf wrote:

[snip]

Yes, the Mac will 'deal' with 32 - 96Khz. Thing is, there's an OS 'gate'
that controls input and output. It's called the Audio Midi Setup
application.

Curious that it has 'midi' in the name as that is something quite
different to dealing with standard LPCM data.

The name is just a MacFoible. The setup application is called "Audio MIDI
Setup", it should be "Audio & MIDI setup". It is where the DacMagic makes
its appearance to configure its feed.

In a fit of enthusiasm, and optimism, I have rushed out and bought a
DacMagic which is now connected via USB to the Mac mini. The Mac Mini is not
bit perfect in this mode, the DacMagic is fed at the bitrate set by the
configuration and not by the bitrate of the file being played, with iTunes.
Now does that matter, time will tell.


I did find this thread attempting to discuss bit perfection which wended its
way to "transparent resampling".

http://www.hydrogenaudio.org/forums/...hp/t60692.html

Some quotes :-

From mixminus1, "While this doesn't prove that OS X and XP are capable of
providing "bit-perfect" output to the sound output device, it seems like a
distinct possibility as I would be surprised if both OSes were performing
transparent resampling.". He actually does not have a clue, it must be bit
perfect because he cannot hear any "artefacts".

One Arnold B Krueger responded with, "Why would you be surprised if a modern
OS did transparent resampling?".

That is point, does it matter. I assume that monkeying around with the
digits is a "bad thing" but can resampling of the sort done in these
computer mixers be done sufficiently well.


The DacMagic has sorted another oddity here. I had doubts about the
Squeezebox being bit perfect, that must be bit perfect because it does not
have a mixer in it in the way that a computer does but that did not stop my
Quad kit from flagging everything as 44.1kHz. The DacMagic gets it right.

--
David Pitt

MessengerPro on iMac, Snow Leopard

Computer-DAC
 

On 11/02/2010 12:14, David Pitt wrote:
Jim wrote:

In a.com, Rob
wrote:
On 10/02/2010 09:22, Jim Lesurf wrote:

[snip]

Yes, the Mac will 'deal' with 32 - 96Khz. Thing is, there's an OS 'gate'
that controls input and output. It's called the Audio Midi Setup
application.

Curious that it has 'midi' in the name as that is something quite
different to dealing with standard LPCM data.

The name is just a MacFoible. The setup application is called "Audio MIDI
Setup", it should be "Audio& MIDI setup". It is where the DacMagic makes
its appearance to configure its feed.


Yep.

In a fit of enthusiasm, and optimism, I have rushed out and bought a
DacMagic which is now connected via USB to the Mac mini. The Mac Mini is not
bit perfect in this mode, the DacMagic is fed at the bitrate set by the
configuration and not by the bitrate of the file being played, with iTunes.
Now does that matter, time will tell.


Well, if the file is the same as the 'iTunes forced mode' (44.1/16),
then I would hope that all's well. Except to say the Dacmagic
*upsamples* for what the bumpf maintains are Very Good Reasons. Just
have to let that one go ;-)

I did find this thread attempting to discuss bit perfection which wended its
way to "transparent resampling".

http://www.hydrogenaudio.org/forums/...hp/t60692.html

Some quotes :-

From mixminus1, "While this doesn't prove that OS X and XP are capable of
providing "bit-perfect" output to the sound output device, it seems like a
distinct possibility as I would be surprised if both OSes were performing
transparent resampling.". He actually does not have a clue, it must be bit
perfect because he cannot hear any "artefacts".

One Arnold B Krueger responded with, "Why would you be surprised if a modern
OS did transparent resampling?".

That is point, does it matter. I assume that monkeying around with the
digits is a "bad thing" but can resampling of the sort done in these
computer mixers be done sufficiently well.


I think I'll just use USB after all. Sounds very good to me. And
something about velvet glove/sow's ear springs to mind.


The DacMagic has sorted another oddity here. I had doubts about the
Squeezebox being bit perfect, that must be bit perfect because it does not
have a mixer in it in the way that a computer does but that did not stop my
Quad kit from flagging everything as 44.1kHz. The DacMagic gets it right.


Yes, no mucking about using it in that application.

Rob

Computer-DAC
 

On 11/02/2010 09:16, Jim Lesurf wrote:
In a.com, Rob
wrote:

On bit perfect: do you/anyone know how it's measured/tested?

I've been though this in recent months. e.g. for

http://www.audiomisc.co.uk/Linux/Sou...Computing.html

http://www.audiomisc.co.uk/Linux/Sou...stenAgain.html


You did, you did, saw that, but it was more a 'which bit of wire do I
connect to what and how do I interpret the data' type thing enquiry.

The key is that you need to have a recorder that can accept the spdif (or
USB) output and record the sample stream. Then compare that with the LPCM
source you are playing on a sample-by-sample basis.

For 44k/16 I've used a Pioneer Audio CD recorder. But am changing to the
Tascam HD P2. One reason being that it can record other sample rates and 24
bit as well as 16.

I then use my own RO and ROX/Linux apps to examine the results. I will be
making copies of the software available in due course so anyone who wishes
can use them. But the key point is to have the ability to record what
emerges from the computer.


Excellent, I'll watch out for that.


Also, I think I read that if the computer software volume control works,
the digital output is not bit perfect.

Yes. It is necessary to set any such control to '0dB' or '100 percent'.
...and also necessary to check that this *does* mean 'gain of unity
applied'. I've encountered cases where 'volume' controls do *not* leave the
data values unchanged for such a setting! I'm afraid that the situation
with computer sound seems a right guddle to me. It seems to be aimed at
assuming ignorant users will have no interest in audio quality. :-/


A guddle indeed. I actually meant that if the software volume *works* -
is active - it's a rough and ready and mainly accurate indication that
the digital stream is being manipulated. The only time this has happened
on the two 'layers' of volume control for the Mac (system and app) was
optical feed to an AV amplifier - so I'd guess and say hgetting the
'pure' signal out is not impossible. But I'd be guessing.

BTW as you can see from the above webpages you need to set '11' on the BBC
iPlayer to stop the iPlayer software from altering the output level. i.e it
uses the 'Spinal Tap' scale. 8-}


Jocular lot the BBC.

Computer-DAC
 

"Rob" wrote in message
om

On bit perfect: do you/anyone know how it's
measured/tested?

Align the two files at the sample level and subtract them. The result must
be zero.

Play a Dolby digital sound track through it and decode it with a Dolby
digital decoder. If you get noise, then its not bit perfect. If you get
music, it is bit perfect.

Computer-DAC
 

In article , Rob
wrote:
On 11/02/2010 12:14, David Pitt wrote:
Jim wrote:


In a fit of enthusiasm, and optimism, I have rushed out and bought a
DacMagic which is now connected via USB to the Mac mini. The Mac Mini
is not bit perfect in this mode, the DacMagic is fed at the bitrate
set by the configuration and not by the bitrate of the file being
played, with iTunes. Now does that matter, time will tell.


Well, if the file is the same as the 'iTunes forced mode' (44.1/16),
then I would hope that all's well. Except to say the Dacmagic
*upsamples* for what the bumpf maintains are Very Good Reasons. Just
have to let that one go ;-)

In principle there is nothing wrong with either 'upsampling' or
'resampling' the audio data. Such processes are common in DACs as part of
the process of generating an *analogue* output - hence situations where you
have to 'process' the data anyway.

This is different to a case where a computer blindly 'resamples' data when
you *don't* need it to. If the DAC can handle the source sample rate, then
it is the steam of source sample values that should be delivered to the DAC
without being 'fiddled about' by the computer.

Again in principle 'resampling' can be done very well, and may be
'harmless'. But in practice it may also be poorly done (as per the examples
on the webpages I gave). Hence needless resampling is just an added
opportunity for the data to be fouled up, and the sound degraded.

One Arnold B Krueger responded with, "Why would you be surprised if a
modern OS did transparent resampling?".

That is point, does it matter. I assume that monkeying around with the
digits is a "bad thing" but can resampling of the sort done in these
computer mixers be done sufficiently well.


Resampling/upsampling as done by a device like a Meridian DAC or the
DACMagic can work very well. The problem is that some computer systems may
crudely 'interpolate' and thus generate distortions.

Indeed, even if resampling is done well it can lead to problems for a
following DAC that doesn't know it was done. So the basic rule is that it
best avoided unless it is employed for a specific purpose, well done, and
the user knows the snags, etc. Yet with computer it tends to be done
without the user being knowing, or being told how the process is being
computed.

I have the feeling that this is all a testament to the standard way
commercial customers of computers are regarded by the OS/hardware makers.
Keep people in ignorance of how what they have bought works so they don't
realise when they may have been short-changed! I've moaned more than once
about the poor quality of 'reviews' in audio mags. But my impression is
that the 'reviews' in computer mags are even less useful.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Computer-DAC
 

In article , David Pitt
wrote:
Jim Lesurf wrote:

done, and the user knows the snags, etc. Yet with computer it tends to
be done without the user being knowing, or being told how the process
is being computed.

In a similar vein, this about Mac OS makes a good read, the author seems
to know what he is talking about.

http://scopeboy.com/scopeblog/?tag=resampling

The article is interesting. But it also indicates the problems.

Firstly the basic error of having a system which imposes resampling when it
may simply not be necessary. If you output to a DAC that can cope with a
range of sample rates then the default should be to send it the source rate
samples. Not impose a needless change with the chances that will degrade
the info.

Secondly, the above gives a link to what is described as if it were a
program, but is actually just sets of coefficient values for use in a
resampling process. No real details of how the process is done.

The problem is then as follows. Is it really the case that every new
resampled value is computed using around 3000 coefficient x input sample
multiply and adds? If so that seems an insanely over demanding method. That
kind of thing is OK for dedicated hardware but sheer blind brute force and
iggorance for a CPU in a general computer *when you could have left the
data alone*.

And what level of accuracy will you then get when using single precision.
How accurate are the coefficients give they aren't in floating format, nor
binary, etc?

So it does look to me like another example of where those working on
general computing just don't understand the problem, and apply irrelevant,
needless, or less than optimum processes.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html