Digital volume control question....
 

Serge Auckland wrote:

I think the nub of your response is that people "believe" things sound
different. It's the same mental process that have people believing in
God, the Tooth Fairy and Santa Claus. They don't have a shred of
objective evidence that things sound different, just their faith.

I'll accept that pots, capacitors, resistors etc. sound different when I
see objective measurements that indicate that there should be a
difference and the results of properly conducted double-blind tests that
show that there was a difference.

S.
S.

http://members.aol.com/sbench102/caps.html

--
Nick

Digital volume control question....
 

Arny Krueger wrote:
"Nick Gorham" wrote in message


Serge Auckland wrote:

Ian Iveson wrote:


The DSP solution would appear to be preferable.
However, presumably there are rounding errors. That is,
if I divide every word by a constant, each result must
be rounded to the nearest step, and this rounding error
is not linear wrt the audio signal. I assume there is a
name for this kind of error? How significant is it?


The DSP solutions I'm familiar with operate either
floating point or 32 or 48 bit internal which means that
when the output is finally reduced to 16 or 24 bit the errors from the
DSP calculations are
minimised. I don't know of a specific name for the
errors resulting from DSP operation.


But even if the internal calculation is done with larger
resolution, you still loose one bit of output resolution
for every 6db of attenuation.


A very similar thing happens with analog level controls. In the real world,
even more so.



Yes, I guess so by definition, but I would hope a quality pot or stepped
attenuator should start with more than 96db worth of resolution.

--
Nick

Digital volume control question....
 

Nick Gorham wrote:
Serge Auckland wrote:

I think the nub of your response is that people "believe" things sound
different. It's the same mental process that have people believing in
God, the Tooth Fairy and Santa Claus. They don't have a shred of
objective evidence that things sound different, just their faith.

I'll accept that pots, capacitors, resistors etc. sound different when I
see objective measurements that indicate that there should be a
difference and the results of properly conducted double-blind tests
that show that there was a difference.

S.
S.

http://members.aol.com/sbench102/caps.html

Interesting. I'll study it in the next day or two.

S.

Digital volume control question....
 

On Tue, 23 May 2006 11:04:47 +0100, Serge Auckland
wrote:

Andy Evans wrote:
As to audio quality, a conductive plastic pot will have zero effect on
audio quality.

Here's another view from Allen Wright (designs amps)
"Vishay cermet are good. One of the biggest con acts has been the
pushing of conductive plastic pots to the audio industry. I don't care
what the brand is - if they make a CP and a cermet (or even a quality
carbon) then my experience is that the cermet KILLS the CP for sonic
quality. The VISHAY cerment (made by their french wing Sfernice))
sounds. like two good fixed resistors, the identical looking CP sounds
like ****! Allen

Oh dear someone else who thinks resistors have a sound.

That's not someone else, it's only Andy............ :-)

A pot, whether cermet, conductive plastic, carbon or whatever is a pure
resistance (discounting irrelevant tiny amounts of capacitance and
inductance- wirewound pots excepted) and consequently are linear to the
limits of measurement. Therefore how any pot can be better than another
for sonic qualities is beyond me. Pots vary in the accuracy of their
law, the noise made when being altered, tracking on stereo, how long
they last before track wear is evident etc. Sonic differences are just
not there.

Agreed. Having built Vishay-based L-pads, full switched attenuators
with Vishays and Holco metal-films with Elma and Farnell 'military'
switches, and used all kinds of pots, including Alps 'Black Beauty'
and yer actual Penny & Giles studio faders, I concur that there's no
audible difference. Stick with switched attenuators for accurate
tracking at all levels, or a decently built pot like the Alps for
'infinite' level adjustment.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Digital volume control question....
 

On Tue, 23 May 2006 12:06:42 +0100, "Keith G"
wrote:


"Serge Auckland" wrote in message
...
Andy Evans wrote:
As to audio quality, a conductive plastic pot will have zero effect on
audio quality.

Here's another view from Allen Wright (designs amps)
"Vishay cermet are good. One of the biggest con acts has been the
pushing of conductive plastic pots to the audio industry. I don't care
what the brand is - if they make a CP and a cermet (or even a quality
carbon) then my experience is that the cermet KILLS the CP for sonic
quality. The VISHAY cerment (made by their french wing Sfernice))
sounds. like two good fixed resistors, the identical looking CP sounds
like ****! Allen

Oh dear someone else who thinks resistors have a sound.

A pot, whether cermet, conductive plastic, carbon or whatever is a pure
resistance (discounting irrelevant tiny amounts of capacitance and
inductance- wirewound pots excepted) and consequently are linear to the
limits of measurement. Therefore how any pot can be better than another
for sonic qualities is beyond me. Pots vary in the accuracy of their law,
the noise made when being altered, tracking on stereo, how long they last
before track wear is evident etc. Sonic differences are just not there.


Interesting that you are never challenged here, Serge. You wouldn't have to
wander far from this group to find a lot people who quite strongly believe
that all components (resistors, caps, pots &c.) can influence the sound from
audio kit.

Indeed so, but that doesn't mean they know in any way shape or form,
what they're talking about! :-) Vide the notorious Andy Evans...

I have no real knowledge and very little experience, so no strong
views - I always say I think it's possible (even likely) different
components will 'sound different', but is it really *hearable*...???

If it's hearable, then they sound different. IME, they don't. Yes, I
have a £250 pot in my passive controller, but I won't be buying
another one, nor would I recommend it to anyone else! It does *feel*
very smooth in operation, however. :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Digital volume control question....
 

On Tue, 23 May 2006 13:12:56 +0100, Eiron wrote:

Serge Auckland wrote:

I think the nub of your response is that people "believe" things sound
different. It's the same mental process that have people believing in
God, the Tooth Fairy and Santa Claus. They don't have a shred of
objective evidence that things sound different, just their faith.

I'll accept that pots, capacitors, resistors etc. sound different when I
see objective measurements that indicate that there should be a
difference and the results of properly conducted double-blind tests that
show that there was a difference.

So is it not the case that metal film resistors have lower noise than carbon ones,
and that this gives an audible and measurable difference in phono and microphone
preamps?

Note that this is a question, not a statement. I haven't measured anything recently.

Yes, it's true, but if you can hear that difference, then you are
using *way* too high value resistors in your phono preamp! You won't
hear resistor noise in any other part of your equipment.

BTW, it's also quite hard to find cracked carbon resistors these days,
carbon film seems to be about the cheapest available, and it's got
very little difference from metal film in the noise department. Active
device noise almost always dominates, expect with low-output MC carts,
where excess resistance in the first stage is to be avoided.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Digital volume control question....
 

"Stewart Pinkerton" wrote in message
...
On Tue, 23 May 2006 12:06:42 +0100, "Keith G"
wrote:


"Serge Auckland" wrote in message
...
Andy Evans wrote:
As to audio quality, a conductive plastic pot will have zero effect on
audio quality.

Here's another view from Allen Wright (designs amps)
"Vishay cermet are good. One of the biggest con acts has been the
pushing of conductive plastic pots to the audio industry. I don't care
what the brand is - if they make a CP and a cermet (or even a quality
carbon) then my experience is that the cermet KILLS the CP for sonic
quality. The VISHAY cerment (made by their french wing Sfernice))
sounds. like two good fixed resistors, the identical looking CP sounds
like ****! Allen

Oh dear someone else who thinks resistors have a sound.

A pot, whether cermet, conductive plastic, carbon or whatever is a pure
resistance (discounting irrelevant tiny amounts of capacitance and
inductance- wirewound pots excepted) and consequently are linear to the
limits of measurement. Therefore how any pot can be better than another
for sonic qualities is beyond me. Pots vary in the accuracy of their
law,
the noise made when being altered, tracking on stereo, how long they
last
before track wear is evident etc. Sonic differences are just not there.


Interesting that you are never challenged here, Serge. You wouldn't have
to
wander far from this group to find a lot people who quite strongly believe
that all components (resistors, caps, pots &c.) can influence the sound
from
audio kit.

Indeed so, but that doesn't mean they know in any way shape or form,
what they're talking about! :-) Vide the notorious Andy Evans...

I have no real knowledge and very little experience, so no strong
views - I always say I think it's possible (even likely) different
components will 'sound different', but is it really *hearable*...???

If it's hearable, then they sound different. IME, they don't. Yes, I
have a £250 pot in my passive controller, but I won't be buying
another one, nor would I recommend it to anyone else! It does *feel*
very smooth in operation, however. :-)


As the only thing between your expensive/irreplaceable speaker drivers
(IIRC) and the full whack from your amp, it's worth every penny if it gives
a lifetime's service and doesn't let go like the cheap one did on my Cheepie
Chinkie amp (on one channel)!! Luckily that was only an inexpensive/easily
replaceable Fostex driver and a low powered amp so no harm done, but you
don't get a whole lot of warning when the music kicks in *flat out*!! :-)

Digital volume control question....
 

Oh dear someone else who thinks resistors have a sound.

That's not someone else, it's only Andy............ :-)

If all the engineers on this group who insist on measurable accuracy in
everything used the same diligence in reading words - maybe not
strictly the domain of whizzing electrons - then it would have been
obvious that this quote came not from me but from Allen Wright, a
respected amp designer and technical author.

Digital volume control question....
 

In article , Nick Gorham
wrote:
Serge Auckland wrote:

I'll accept that pots, capacitors, resistors etc. sound different when
I see objective measurements that indicate that there should be a
difference and the results of properly conducted double-blind tests
that show that there was a difference.


http://members.aol.com/sbench102/caps.html

I've only had a quick look at the above, and the pages linked to it.
However they don't seem to me to be particularly relevant to the question
of capacitors normally having a 'sound' in normal use.

The first thing that struck me about the page was the following which I
quote:

"The signal level was held constant at about 70 volts RMS at 600 Hz across
the capacitors. (for about 26mA signal current). This is probably more
than you would normally expect,..."

My reaction to the last phrase was,,, "indeed!" :-)

I can't recall ever building or using an audio amplifier or tuner that had
anything like this large an *audio voltage* across any of the *capacitors*.
Note the above is 70v RMS *between the capacitor terminals*. i.e. not just
an input where most of the voltage appears elsewhere. I have certainly
built (and use!) amps which have audio voltages this large inside them, but
not between the terminals of any of the signal capacitors.

Given the above, the plots are hardly surprising. Indeed, they seem to me
to agree with work by Doug Self, who simply concluded that we should
avoid significant ac across any of the capacitors in the signal
paths if we used caps like electrolytics. In general, this is quite easy in
my experience.

FWIW The results also seem to agree with measurements I've seen published
elsewhere, and with those which one my honours project students obtained
some years ago in similar tests.

Also, the nonlinearities shown would produce easily measureable levels of
THD. However if you measure many amps that have capacitors in the signal
paths they deliver far lower levels of nonlinearity even when the caps are
outwith any feedback loops. The reason simply being that the ac voltages
on the caps are orders of magnitude smaller than 70v RMS.

I can have a more careful read of the page(s) if anyone thinks it
worthwhile, but I can also comment on another quote:

"The "current monitor" resistor used for all curves was 100 ohms. The
"integrator" was passive, using a 100k and 0.047, 0.1, or 0.47 uF
capacitors depending on the frequency and level. The "X" input to the
scope was fed with an additional series capacitor and adjusted for exactly
"90 degrees" phase shift (typically ran 0.01u into the 10 meg scope probe
resistance) to reduce systemic errors. The generator is absolutely
isolated, being the secondary of a transformer capable of 300 volts into
1k from 15Hz to 1kHz. The bias voltage was added "in series" with
this from an HP regulated and isolated supply. The junction of the current
monitor resistor and the capacitor under test serves as the scope and
system "reference" point."

For a measurement engineer/scientist the above would prompt many questions.
It is not at all clear if any of the results arise due to imperfections in
the system described as we are not given the details of any other tests
used to calibrate or assure the performance of the measurement system. If
caps have such effects, it seems a shame to have so many in the measurement
system without having any info on what effects *they* may be producing...

However can anyone say what domestic amps actually employ ac audio signals
across the signal caps that are this large in nomal use at frequencies like
600Hz? If not, I am not sure why the results show anything about what may
be 'audible' in real amplifiers, etc.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Digital volume control question....
 

Jim Lesurf wrote:
In article , Nick Gorham
wrote:
Serge Auckland wrote:

I'll accept that pots, capacitors, resistors etc. sound different when
I see objective measurements that indicate that there should be a
difference and the results of properly conducted double-blind tests
that show that there was a difference.


http://members.aol.com/sbench102/caps.html

I've only had a quick look at the above, and the pages linked to it.
However they don't seem to me to be particularly relevant to the question
of capacitors normally having a 'sound' in normal use.

The first thing that struck me about the page was the following which I
quote:

"The signal level was held constant at about 70 volts RMS at 600 Hz across
the capacitors. (for about 26mA signal current). This is probably more
than you would normally expect,..."

My reaction to the last phrase was,,, "indeed!" :-)

I can't recall ever building or using an audio amplifier or tuner that had
anything like this large an *audio voltage* across any of the *capacitors*.
Note the above is 70v RMS *between the capacitor terminals*. i.e. not just
an input where most of the voltage appears elsewhere. I have certainly
built (and use!) amps which have audio voltages this large inside them, but
not between the terminals of any of the signal capacitors.

Given the above, the plots are hardly surprising. Indeed, they seem to me
to agree with work by Doug Self, who simply concluded that we should
avoid significant ac across any of the capacitors in the signal
paths if we used caps like electrolytics. In general, this is quite easy in
my experience.

FWIW The results also seem to agree with measurements I've seen published
elsewhere, and with those which one my honours project students obtained
some years ago in similar tests.

Also, the nonlinearities shown would produce easily measureable levels of
THD. However if you measure many amps that have capacitors in the signal
paths they deliver far lower levels of nonlinearity even when the caps are
outwith any feedback loops. The reason simply being that the ac voltages
on the caps are orders of magnitude smaller than 70v RMS.

I can have a more careful read of the page(s) if anyone thinks it
worthwhile, but I can also comment on another quote:

"The "current monitor" resistor used for all curves was 100 ohms. The
"integrator" was passive, using a 100k and 0.047, 0.1, or 0.47 uF
capacitors depending on the frequency and level. The "X" input to the
scope was fed with an additional series capacitor and adjusted for exactly
"90 degrees" phase shift (typically ran 0.01u into the 10 meg scope probe
resistance) to reduce systemic errors. The generator is absolutely
isolated, being the secondary of a transformer capable of 300 volts into
1k from 15Hz to 1kHz. The bias voltage was added "in series" with
this from an HP regulated and isolated supply. The junction of the current
monitor resistor and the capacitor under test serves as the scope and
system "reference" point."

For a measurement engineer/scientist the above would prompt many questions.
It is not at all clear if any of the results arise due to imperfections in
the system described as we are not given the details of any other tests
used to calibrate or assure the performance of the measurement system. If
caps have such effects, it seems a shame to have so many in the measurement
system without having any info on what effects *they* may be producing...

However can anyone say what domestic amps actually employ ac audio signals
across the signal caps that are this large in nomal use at frequencies like
600Hz? If not, I am not sure why the results show anything about what may
be 'audible' in real amplifiers, etc.

Slainte,

Jim

Jim, you took the words right out of my keyboard.

I have never measured any increase in THD with a capacitor in circuit in
the amplifiers I have designed. This is true of all sorts of cap,
electrolytic, tantalum, polyester, polystyrene. Polar capacitors need to
be well polarised or they do perform badly, but otherwise, no change in
distortion was ever measured to the limits of my measuring instruments.
I have not been concious of capacitors adding noise, so conclude that
any changes in performance caused by capacitors must be so far below
other sources of noise and distortion that they can safely be ignored as
having a sonic signature that is perceivable. That's not to say that
one can use any old capacitor anywhere, given that leakage currents are
greater with some caps, internal inductance can be high with some types
and, for example, for decoupling high-speed ICs, physically small low
inductance types need to be fitted close to the IC pins, so that often
determines the type to be used.

S.