New webpage on BBC iPlayer measurements / Linux
 

Jim Lesurf wrote:
In article , Rob
wrote:
Jim Lesurf wrote:

snip


For reasons I don't need to understand, I take it it's better not to use
any volume control on the computer that affects the volume of a digital
output other than set it at maximum?

Alas, not quite. The trick is to establish the settings for the computer
and its software that pass though digital values with no rescaling of the
amplitude of the values. This may be 'maximum', but that depends entirely
on how the programmers wrote the software, etc. If they don't tell you, you
are left to guess, or experiment, or measure.

With the specific systems I tried - that were Linux based - I found that
setting levels to '100%' (or '0dB') did this. So that is a good bet. But as
shown by the problem I found with headphones you can't be certain in
advance that some pinheaded software or hardware engineer hasn't upset this
and some other value is better.


Using analogue PC outputs, OK, gotcha.

Using digital PC outputs, does the same apply?

As it happens, I'm using USB to DAC right now. Volume can be controlled
in 3 ways. Using the OS software (OS X) and the 'volume control'
application. The media player software's (iTunes) volume control. Or the
amplifier. So I think you're saying I need to do some analysis along the
lines of your tests.


FWIW if I can blag a borrow I will try out some other USB 'soundcards'
to see how they work (if at all!) with Linux. Then report on what I
find out. A number of these have appeared recently. But I've only seen
limited results based on windows and macs.


If I get round to it, and you can return it at some point, you can
gladly borrow an Opcode Sonicport (bus powered USB DAC). Works natively
on a Mac and Windows Vista (but not XP). I got it from a recording place
round the back of Denmark St - I'd guess it had a sort of claim to
goodness at some point.

I may be interested at some point. Afraid I've not heard of it. Is it a
currently available USB DAC? How does it identify itself on a windows box?


I'm pretty sure it's Opcode Sonicport. On the Mac it's reported as:

Product ID: 0xa011
Vendor ID: 0x06f1
Version: 1.00
Serial Number: SONICport
Speed: Up to 12 Mb/sec
Manufacturer: Opcode Systems Inc
Location ID: 0x1d100000
Current Available (mA): 500
Current Required (mA): 240




The DACMagic is excellent in my opinion.


[snip]

Is it too much to ask for a standard?

Afraid I don't know what you are asking here.


The 'hidden snags' of computer-based systems to be removed/standardised,
and a standard produced. Idiots like me would no longer need to guess
when choosing digital.

Anyhow, do you mean this:

http://www.cambridgeaudio.com/summar...&Title=Summary

Yes.

It's £250. Ebay has DACs for £30 - Mini HIFI SPDIF+OPTICAL
DAC--PCM1793+DIR9001+OPA2134. What's the critical part of the component
here? It's not the DAC itself presumably - it's the analogue
amplification?

No, the vital part in this context is the chip or other interface that
receives the USB audio. It has to identify itself to the computer in a way
that allows the data transfers to proceed correctly.

I (still!) have problems understanding why one digital component
necessarily sounds different compared to another *unless* it's to do
with analogue amplification. And I don't really follow that - just seems
to make sense.

The problem with USB DACs is as above. But with computer based systems all
kinds of other things can go wrong. For example the stream of values may be
'resampled' or otherwise fudged about by the system. So that what comes out
isn't what went in, even as a series of digital values.


Ah, OK. So the digital output of a PC is much of a muchness *if* the
sampling isn't altered?

I was tempted by the fit-pc2 as it is said to run with Linux, is small
and silent, and I can use an external DAC. But I've since been told it
doesn't currently work with Ubuntu 9.04 and has various hardware
snags. So no cigar unless the snags are sorted.


Ah - that's me wrong again! The netbook has an Atom processor and is
pretty clunky with Windows XP - and as I say, uses a fan which does kick
in frequently.

The good news is that many Linux distrbutions are somewhat less demanding
than Windows, so don't stress machines as much. But that may not matter
much if you then run tasks that are demanding. e.g. Processing video is
likely to be demanding regardless of OS. But I'd suspect that even a very
low spec machine should cope with simply passing around LPCM with no
processing without having to struggle.

Seems those Fit-PC2s have some sort of clever convection
cooling perhaps. Macs have very impressive cooling IME. Even the
desktop iMac (dual core Intel, fast HD, and decent graphics) has 3 fans
that 'trickle' at around 1200rpm and produce a very unobtrusive sshhh.
The HD is silent. Room temp in here is 23C, CPU is 38C.

The Shuttle I am using has a large, low speed fan that is meant to be
'quiet'. But I disconnected it to ensure silence. 8-] This is OK as what
I use the machine for isn't demanding for long periods, so only runs the
CPU at a small fraction of the level it can nominally deliver.


Yep, reasonable plan. That wouldn't quite do for me though - I
occasionally use the quiet media computer for processor intensive things.

I also had a SSD fitted, not a traditional Magnetic HD. So no HD noises,
either.


That's the way - silent and lower heat. Apparently (from limited
reading) power consumption is about the same as a magnetic drive, and
performance is a mixed bag. SSDs would be extortionate for my use
anyway: 400GB of media.

Although the Mac Mini is by no means silent it's only really audible at
about 2m. The TV and SS amplifier make more noticeable noise. The valve
amp is silent :-)

Rob

New webpage on BBC iPlayer measurements / Linux
 

In article , Rob
wrote:
Jim Lesurf wrote:
In article , Rob
wrote:

With the specific systems I tried - that were Linux based - I found
that setting levels to '100%' (or '0dB') did this. So that is a good
bet. But as shown by the problem I found with headphones you can't be
certain in advance that some pinheaded software or hardware engineer
hasn't upset this and some other value is better.


Using analogue PC outputs, OK, gotcha.

Using digital PC outputs, does the same apply?

I can't be sure. But I'd suspect that setting everything to '100%' or '0dB'
would be best. So the choice to make unless/until you have evidence to the
contrary. Only way to be sure is the measure the specific setup, including
the application software being used.

As it happens, I'm using USB to DAC right now. Volume can be controlled
in 3 ways. Using the OS software (OS X) and the 'volume control'
application. The media player software's (iTunes) volume control. Or the
amplifier. So I think you're saying I need to do some analysis along
the lines of your tests.

Yes. The critical test is to have LPCM source files, play those, and be
able to record the *digital* output. Then compare the recorded series of
values with the series in the source file. If they agree exactly as a
series of values, then that is a good sign. The snag is that you need a
reliable way to record the output and compare it with the source.

IIRC when I did the previous Linux audio pages a Windows app was mentioned
that should allow 'loopback' recordings. That may do the trick, but I can't
say as I have never tried the application in question. Afraid I've now
forgotten what the application program was called, though.


If I get round to it, and you can return it at some point, you can
gladly borrow an Opcode Sonicport (bus powered USB DAC). Works
natively on a Mac and Windows Vista (but not XP). I got it from a
recording place round the back of Denmark St - I'd guess it had a
sort of claim to goodness at some point.

I may be interested at some point. Afraid I've not heard of it. Is it
a currently available USB DAC? How does it identify itself on a
windows box?


I'm pretty sure it's Opcode Sonicport. On the Mac it's reported as:

Product ID: 0xa011 Vendor ID: 0x06f1 Version: 1.00 Serial Number:
SONICport Speed: Up to 12 Mb/sec Manufacturer: Opcode Systems Inc
Location ID: 0x1d100000 Current Available (mA): 500 Current Required
(mA): 240

OK. I'll see if I can find if it is already listed anywhere as working with
Linux distributions.


Is it too much to ask for a standard?

Afraid I don't know what you are asking here.


The 'hidden snags' of computer-based systems to be removed/standardised,
and a standard produced. Idiots like me would no longer need to guess
when choosing digital.

OK. Yes, I agree. There really should be some openly defined and followed
standards for things like this. Alas, MicroSoft tend to make up their own
'standards' as they go along, keep them confidential, and change them
without any notice or concern.

The Linux community at least has a more open and co-operative approach. The
drawback is that they tend to produce multiple 'standards' that don't
always fit together. Plus you sometimes need to be a real geek to make any
sense of the 'documentation and manuals' which seem often to require you to
know what they mean before you read them. 8-]

So in this case we have a series of 'sound systems'. ALSA is the
longest-established, but others can work better in specific cases. Hence my
finding I needed to switch to PulseAudio to get the iPlayer Flash plugin to
talk to my USB DAC! I could probably have got it working with ALSA, but
with more furtling about. I suspect Ubuntu 9.10 will have fixed this
problem, but time will tell...


I (still!) have problems understanding why one digital component
necessarily sounds different compared to another *unless* it's to do
with analogue amplification. And I don't really follow that - just
seems to make sense.

The problem with USB DACs is as above. But with computer based systems
all kinds of other things can go wrong. For example the stream of
values may be 'resampled' or otherwise fudged about by the system. So
that what comes out isn't what went in, even as a series of digital
values.


Ah, OK. So the digital output of a PC is much of a muchness *if* the
sampling isn't altered?

With LPCM that *should* be so - but as usual I can't be certain in any
given case. With source material in 'compressed' forms like mp3 the results
may well change with the software used.

FWIW I have also been doing some comparisons with lossy compression
sources, etc. But as yet no-where near having any sensible conclusions I
could write up.[1]


The Shuttle I am using has a large, low speed fan that is meant to be
'quiet'. But I disconnected it to ensure silence. 8-] This is OK as
what I use the machine for isn't demanding for long periods, so only
runs the CPU at a small fraction of the level it can nominally deliver.


Yep, reasonable plan. That wouldn't quite do for me though - I
occasionally use the quiet media computer for processor intensive things.

That can be OK if the CPU throttles down when hot. But that means things
take longer. The problem is a risk of overheating if the CPU speed stays
high and the chip gets overheated.

I don't use the Shuttle for any CPU intense things. If I need that I'd use
another machine. I have no interest in video at present so far as computing
is concerned.

I also had a SSD fitted, not a traditional Magnetic HD. So no HD
noises, either.


That's the way - silent and lower heat. Apparently (from limited
reading) power consumption is about the same as a magnetic drive, and
performance is a mixed bag. SSDs would be extortionate for my use
anyway: 400GB of media.

The one I have is 60GB which is fine for the use I am putting it to. In
fact I have it divided 30/30 for two different Linux OS distributions for
experimental purposes. Although I am currently using Ubuntu 9.04 and ROX
for day-to-day audio listening and recording.

For other off-machine storage I can always get removable USB devices.
Doesn't matter if they make a noise since they would only be connected and
powered when I wanted to transfer loads of data to/from them. For me 20GB
or so of main HD space free is fine with the Shuttle as I only need to keep
a few files at a time on it.

I also suspect that during the next few years the cost of SSD will drop
like a rock and the device sizes will expand.

Slainte,

Jim

[1] Been distracted by something quite different: Ben Duncan and Mains
Cables. :-)

--
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

New webpage on BBC iPlayer measurements / Linux
 

"Rob" wrote in message
om...

Although the Mac Mini is by no means silent it's only really audible at
about 2m.

I can vouch for that, and mine has a retrofitted 320GB WD 7200rpm HD.

Patrick Wallace
__________________________________________________ ______

New webpage on BBC iPlayer measurements / Linux
 

In article , Patrick Wallace
wrote:

"Rob" wrote in message
om...

Although the Mac Mini is by no means silent it's only really audible
at about 2m.

I can vouch for that, and mine has a retrofitted 320GB WD 7200rpm HD.

Alas, the above has two snags for me.

One is that I sit closer than 2m to some of the kit I use when listeing to
audio. Although I am about 3m from the Shuttle I am using in the hifi room
system.

The other is the meaning of "really audible". I can often hear the mains
transformers buzzing in even quite (allegedly) good items of audio
equipment. So often have to dissasemble and modify items to make them
slient. Similarly, can hear the disc rotating in some audio CD/DVD players.

Much of my listening is to 'classical' music that can have long ppp (or
quieter) passages, or pauses. At such times extraneous sounds which would
not be noticed in other situations becomes all too obvious to me.

So far as I am concerned, if someone is to pay hundreds of pounds for
equipment for domestic audio use, then the equipment should be mechanically
*silent*. i.e. even when there is no music or other noises you can't hear
the equipment when right beside it. It is clearly possible to do this as
some items of equipment do it.

Indeed, this can't be ultra-hard since dedicated devices like the Roberts
'net radio' I've been playing with recently has no fans and makes no
mechanical noises. Alas, that has other drawbacks from my POV.

TBH I also am reluctant to pay extra for items to have a 'Mac badge' since
I have no interest in using MacOS.

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