Anyone here familiar with so-called 'zipper noise' in audioremote/automation level control applicati

[Eeyore]

If so there's a quick question I'd like to run by you.

Graham

 

[Paul Probert]

If so there's a quick question I'd like to run by you.

Graham

Are you talking about "motorboating", which you get by biasing a single
sided opamp audio circuit by just resistively dividing the power rail?
When I turn on a circuit I built that way it does sound like a zipper,
ie a run of pulses chirping upward in frequency.

Paul

 

[Phil Allison]

"Eeysore Red Hot Fuckwit "

If so there's a quick question I'd like to run by you.

** GIANT HUH ???????????

So - this demented, stuffed donkey wants someone to declare they already
know the answer to a question he has not yet posted.

Don't' play any such stupid games with this ridiculous TROLL.



..... Phil

 

[Eeyore]

Are you talking about "motorboating", which you get by biasing a single
sided opamp audio circuit by just resistively dividing the power rail?
When I turn on a circuit I built that way it does sound like a zipper,
ie a run of pulses chirping upward in frequency.

You're referring to power rail modulation classicly caused by insuffient
local supply decoupling I take it ?

Zipper noise is another effect, essentially a fast series of 'Fourier
clicks' typically caused by a moderately rapid sequence of step gain
changes in audio level in a 'fade-out' for example, so called because it
sounds like the zip on your jeans or whatever. When using a VCA gain
element it can be 'smoothed' somewhat by RC filtering of the control
voltage but is inherent in DSP and can only be removed there by making the
step size very small and therefore all but inaudible.

Graham

 

[Eeyore]

"Eeysore Red Hot Fuckwit "

** GIANT HUH ???????????

So - this demented, stuffed donkey wants someone to declare they already
know the answer to a question he has not yet posted.

Don't' play any such stupid games with this ridiculous TROLL.

Phil's there a mathematical treatment of the analysis of this noise that I
believe may be sufficient to 'prove' that a TI chip, the PGA2310 would not be
suitable for automated / remote level control because of the limited number of
steps (256) even though they are only 0.5dB each. I suspect it may still
produce zipper noise because the step size, although 0.5dB step despite
sounding small there are still only 256 of them (which is a classic number for
producing zipper noise) and TI are I suspect foolishly mis-promoting it in the
pro-audio market.

It would doubtless be fine for slow level changes but not fast ones.

Graham

 

[Eeyore]

The first digital pots were rather bad; two sources (1) not many
steps = large step function in "analog" output and (2) large gate
capacitance coupling on/off step voltage to source/drain.
The newer ones are better, but i would use a scope synched with the
digital command pulse, tie each end of pot to resistor to ground where
resistance is equal to that of pot; scope probe to "tap" / "output".
Should give you an idea as to how good/bad that coupling is.

Shouldn't be a coupling noise in this case, the gain chip is from TI's BB
division who ought to know better. It's the step size that concerns me.

I did a simplistic calculation which suggested the transient zipper noise
involved with 0.5dB steps may be as bad as -20 ish dB which is absurdly
poor for the design in question.

Graham

 

[Eeyore]

Anyone here familiar with so-called 'zipper noise' in audio
remote/automation level control applications ?

I am very familiar with it. The usual quick and dirty fixes are:

[1] Use lots of bits / high resolution.

[2] Slew-rate limit the fader so that is someone slams
the pot from bottom to top it doesn't skip too many steps.
This decreases zipper noise at the cost of increasing lag.

[3] If it's a gain applied to a analog su=ignal, Do the
actual gain switching at zero crossing. )Note: may conflict
with [2])

[3] If the entire signal chain is digital, de-zipper the
gain change by interpolating a bunch of small steps in software
between the larger steps from the fader hardware.

[4] Watch the gain structure so the system isn't using
the bottom 1% of the fader and following it with high gain
elsewhere.

BTW, if you are doing wolume control in a Windows program, read this:
http://blogs.msdn.com/larryosterman/archive/2005/06/16/429820.aspx

If so there's a quick question I'd like to run by you.

Glad to help any way I can...

Sounds like you're my man. I've been up late so will explain later in
more detail.

Graham

 

[Phil Allison]

"Eeysore Red Hot Fuckwit "

Phil's there a mathematical treatment of the analysis of this noise that I
believe may be sufficient to 'prove' that a TI chip, the PGA2310 would not
be
suitable for automated / remote level control because of the limited
number of
steps (256) even though they are only 0.5dB each. I suspect it may still
produce zipper noise because the step size, although 0.5dB step despite
sounding small there are still only 256 of them (which is a classic number
for
producing zipper noise) and TI are I suspect foolishly mis-promoting it in
the
pro-audio market.

It would doubtless be fine for slow level changes but not fast ones.

** Never heard timing the steps to coincide with zero crossings of the
signal ???

Standard practice is all but low end AV gear.

Read the data sheet - dickhead.



...... Phil

 

[Martin Griffith]

Phil's there a mathematical treatment of the analysis of this noise that I
believe may be sufficient to 'prove' that a TI chip, the PGA2310 would not be
suitable for automated / remote level control because of the limited number of
steps (256) even though they are only 0.5dB each. I suspect it may still
produce zipper noise because the step size, although 0.5dB step despite
sounding small there are still only 256 of them (which is a classic number for
producing zipper noise) and TI are I suspect foolishly mis-promoting it in the
pro-audio market.

It would doubtless be fine for slow level changes but not fast ones.

Graham

It's expensive, as well.They should have reduced to step size

Did something similar in the 80's, ended up with 2 multiplying dacs
with some soft FET switching, so you would update the off channel, do
a soft switch, say 1msec to the updated dac
Quite messy
I still like the alps motorised volume controls, (silly) but they
don't have a feedback/position sensor

martin

 

[IanM]

BTW, if you are doing wolume control in a Windows program, read this:
http://blogs.msdn.com/larryosterman/archive/2005/06/16/429820.aspx

Thanks for that, I now have a nice taper on my laptop volume control

Ian

 

[Eeyore]

"Eeysore Red Hot Fuckwit "

** Never heard timing the steps to coincide with zero crossings of the
signal ???
Yes.


Standard practice is all but low end AV gear.

Read the data sheet - dickhead.

And what happens when it times out eh ?

ZERO CROSSING DETECTION
The PGA2310 includes a zero crossing detection function
that can provide for noise-free level transitions. The
concept is to change gain settings on a zero crossing of the
input signal, thus minimizing audible glitches. This
function is enabled or disabled using the ZCEN input
(pin 1). When ZCEN is low, zero crossing detection is
disabled. When ZCEN is high, zero crossing detection will
be enabled.
The zero crossing detection takes effect with a change in
gain setting for a corresponding channel. The new gain
setting will not be latched until either two zero crossings
are detected, or a timeout period of 16ms has elapsed
without detecting two zero crossings. ****In the case of a
timeout, the new gain setting takes effect with no attempt
to minimize audible artifacts.****

Suggest you read the datasheet. Page 10

Graham

 

[[email protected]]

If so there's a quick question I'd like to run by you.

Graham

I have read an article about "gating" the update of level with zero
crossings
to eliminate it.

-Lasse

 

[Eeyore]

It's expensive, as well.They should have reduced to step size

Did something similar in the 80's, ended up with 2 multiplying dacs
with some soft FET switching, so you would update the off channel, do
a soft switch, say 1msec to the updated dac
Quite messy

I follow you and can quite believe it.

I still like the alps motorised volume controls, (silly) but they
don't have a feedback/position sensor

That's silly of them. In this case however the objective is to get a near perfectly
matched stereo (or multi-channel) volume control which is DC controlled (obviously
using an A-D) but I don't think the results will be adequate for pro-audio fades
etc. And it is *high-end* pro-audio.

Totally agree with your comment about the step size and it would have nice if they
soft switched in the PGA.

Graham

 

[Eeyore]

Hello Mr Rabbit

That what you call 'zipper noise', is familiar to me.
You find it for example in my sound blaster (EMU10) based sound card, when moving the slider.
Now a few interesting points:
This sound card also does zipper noise when silence, so you hear indeed
a zipper like noise when the slider moves.
So the design of the attenuator sucks (Hello Creative Labs).

So, first you should make sure changing attenuator steps (in hardware or software)
does not cause a signal by itself.

Second, and this is something I have only tested in a *light* related application,
perhaps you should, or could, switch amplitude only on the zero crossings of the audio
signal.
This would mean worst case for 20 Hz every 50 milli seconds,

Exactly the problem. 50ms is too slow. And the chip has a 16ms Timeout in this mode.

"ZERO CROSSING DETECTION
The PGA2310 includes a zero crossing detection function
that can provide for noise-free level transitions. The
concept is to change gain settings on a zero crossing of the
input signal, thus minimizing audible glitches.

NB - minimising not eliminating.

This function is enabled or disabled using the ZCEN input
(pin 1). When ZCEN is low, zero crossing detection is
disabled. When ZCEN is high, zero crossing detection will
be enabled.
The zero crossing detection takes effect with a change in
gain setting for a corresponding channel. The new gain
setting will not be latched until either two zero crossings
are detected, or a timeout period of 16ms has elapsed
without detecting two zero crossings. ****In the case of a
timeout, the new gain setting takes effect with no attempt
to minimize audible artifacts.****"

So if the slider moved a lot in those 50 milli seconds, then you would have to move
a bit more at once, but during the zero crossing.
This does actually prevent higher harmonics switching noise.
I patent this solution hereby, and just because you insulted me and other people
in your previous rabbit posting, you own me 1000 Internet Credits for every
device you sell that uses my solution.

I am a bit surprised though that an audiophool genius like you cannot fix a simple
issue like that all by himself.

A step volume change even at zero cross still results in an instantaneous change in dV/dt which
is still audible and therefore does not solve the basic problem. Also it's not a fade. Fades are
required.


Graham

 

[Rich Grise]

If so there's a quick question I'd like to run by you.

Well I don't know of you've ever herd of the AY3-something or other
sound generator; it had a tone generator and a 4-bit digital attenuator.
You could program it to make a "beep" sound; that was trivially easy.
But once I wrote a little driver that would simulate a "ding" by doing the
"beep" and stepping the attenuator on that standard e^-t time constant
thing; but with only 16 steps, it sounded a little raggedy. That could
be "zipper noise", depending on what's caught in your zipper! ;-D

Is that what you're talking about?

Cheers!
Rich

 

[Martin Griffith]

I follow you and can quite believe it.



That's silly of them. In this case however the objective is to get a near perfectly
matched stereo (or multi-channel) volume control which is DC controlled (obviously
using an A-D) but I don't think the results will be adequate for pro-audio fades
etc. And it is *high-end* pro-audio.

Totally agree with your comment about the step size and it would have nice if they
soft switched in the PGA.

Graham

I've got a complete 6 channel eurocard PCB design using PGA2310's
somewhere, (I never finished the software though).
There was a wolfson chip now obselete, which looked stunning compared
to the TI/BB offering wm 8816? I think someone bought the design from
wolfson

back to my DAC version, (it was for a analogue eq with recall) I think
I had some sucess by putting a little sample and hold that was
switched in during the transition that reduced the glitches by about
30dB, basically a LPF.

Arn't the THAT VCA's good enough?

martin

 

[Eeyore]

I have read an article about "gating" the update of level with zero
crossings to eliminate it.

Put some bass through it and consider how many zero crossings (and how
much time) it'll take to ramp the level down inaudibly. Delay is
unacceptable.

I can only see a viable option being running quickly through all 256 0.5
dB steps. But I'm convinced this will 'zipper'.

Graham

 

[Eeyore]

Eeyore wrote in


It actually does solve the problem, and anyways 20Hz = 50ms period time, is a zero every 25 mS.

And the chip wants to see TWO zero crossings. But it times out after 16ms.

Especially for a fade that happens slowly that should pose no problems.
You could do some math and get slider speed and extrapolate / interpolate a bit too.

If you look for 'eliminating' well, as I have stated, I am no audiophool, and
think that most people will be more then satisfied with the zero crossing solution.

Looked up the PGA2310 datasheet, not bad.
Maybe you have to design your own circuit to work around those 16 ms.
Next time also specify what chip you are using before you ask, and try
reading its datasheet.

It was someone else's idea and I'm the one saying "hang on a sec, this isn't going to be adequate".
About a few minutes into reading the datasheet in fact. The originator of the idea is somewhat younger
and less experienced you see. Different approach required IMHO.

Fortunately TI do an (inexpensive - well $99) EV Board - so we can actually put 20Hz through it and
see what happens.

Graham

 

[Eeyore]

Well I don't know of you've ever herd of the AY3-something or other
sound generator; it had a tone generator and a 4-bit digital attenuator.
You could program it to make a "beep" sound; that was trivially easy.
But once I wrote a little driver that would simulate a "ding" by doing the
"beep" and stepping the attenuator on that standard e^-t time constant
thing; but with only 16 steps, it sounded a little raggedy. That could
be "zipper noise", depending on what's caught in your zipper! ;-D

Is that what you're talking about?

That's the kind of thing. It's caused by a succession of step changes in
amplitude.

Graham

 

[Eeyore]

I've got a complete 6 channel eurocard PCB design using PGA2310's
somewhere, (I never finished the software though).
There was a wolfson chip now obselete, which looked stunning compared
to the TI/BB offering wm 8816? I think someone bought the design from
wolfson

back to my DAC version, (it was for a analogue eq with recall) I think
I had some sucess by putting a little sample and hold that was
switched in during the transition that reduced the glitches by about
30dB, basically a LPF.

Arn't the THAT VCA's good enough?

That's already an alternative suggestion I've made. Thanks Martin. Believe it or not all
this was to try and get 'low cost' matched level controls. Yes, they can do that but
it's for mixing and lag or zipper noise is not acceptable. The originator of the idea
hadn't fully thought it through it seems. And don't forget the predominance of bass in
much music makes the zero-crossing method useless on account of the timeout.

Graham