E
Eeyore
Guy said:Eeyore said: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.
Would do if I had them. Only 8 bits of control on the TI PGA2310.
[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.
Unacceptable for mixing.
[3] If it's a gain applied to a analog signal, Do the
actual gain switching at zero crossing. )Note: may conflict
with [2])
It does conflict, especially at low frequencies. And it still causes an
audible change in dV/dt.
[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.
Yes, would do but it isn't. It's an analogue signal chain in fact.
[4] Watch the gain structure so the system isn't using
the bottom 1% of the fader and following it with high gain
elsewhere.
Definitely not !
From the other replies you'll probably get the gist of the problem.
In the early days of automated consoles especially, IIRC, 256 discrete
steps would cause zipper noise. Filtering the VCA control input could
make it acceptable but a PGA2310 isn't that kind of chip. Not sure what
control law was being used but if you still only have 256 steps, surely
the same problem exists regardless of the law, it simply moves the
problem around ?
So, digital fails to deliver. I could do it in 24 bit DSP but it would be
plain silly for a volume control. 48kHz sampling would most certainly NOT
be acceptable either so the low cost chips would be out.
Graham