Re: [LAD] Mixing audio: Noiseless volume changes

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To: <linux-audio-dev@...>
Date: Tuesday, March 19, 2013 - 10:26 pm

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On Tue, Mar 19, 2013 at 2:15 PM, Tim Goetze wrote:

> [Fons Adriaensen]

You guys are splitting hairs... kind of misses the forest for the trees.
Here's my nit to pick: two identical 1st-order lowpass filters in series
are only equivalent to a 2nd-order lowpass filter when the quality factor
is 0.5. So that's not the same thing.

The best way to avoid "zipper noise" is not to create it in the first
place. Ramps not good enough for ya? Why not? Any "slow enough" ramp
will do. Your problem might be that you're trying to ramp the volume too
fast. Adding a filter just slows down the response anyway.

I think you should figure out a different shape of ramp that doesn't have
discontinuities in the first derivative, such as:

0.5-0.5*cos(pi*n/N)
where N is the number of samples in the ramp

If simple guesses like that are not good enough, you'll have to figure out
how to make a bandlimited step function that cuts out the problematic
frequencies.

Chuck

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On Tue, Mar 19, 2013 at 2:15 PM, Tim Goetze <<=
a href=3D"mailto:tim@quitte.de" target=3D"_blank">tim@quitte.de> wrote:
[Fons Adriaensen]

ed to be computed

Ah yes, sorry, I see that now.

If that extra operation comes around to bite hard enough, I'll be sure<=
br>
to chain two 1st-order lowpass filters.You guys are splitting hairs... kind of misses the forest for the trees.=
=A0 Here's my nit to pick: two identical 1st-order lowpass filters in s=
eries are only equivalent to a 2nd-order lowpass filter when the quality fa=
ctor is 0.5.=A0 So that's not the same thing.
The best way to avoid "zipper noise" is not to cre=
ate it in the first place.=A0=A0 Ramps not good enough for ya?=A0 Why not?=
=A0 Any "slow enough" ramp will do.=A0 Your problem might be that=
you're trying to ramp the volume too fast.=A0 Adding a filter just slo=
ws down the response anyway.
I think you should figure out a different shape o=
f ramp that doesn't have discontinuities in the first derivative, such =
as:0.5-0.5*cos(pi*n/N)where N is the numb=
er of samples in the ramp
If simple guesses like that are not good enough, =
you'll have to figure out how to make a bandlimited step function that =
cuts out the problematic frequencies.Chuck

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Messages in current thread:
[LAD] Mixing audio: Noiseless volume changes, Tim E. Real, (Mon Mar 18, 9:50 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Mon Mar 18, 11:05 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Paul Davis, (Mon Mar 18, 10:47 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Tim E. Real, (Mon Mar 18, 11:05 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Tim E. Real, (Mon Mar 18, 11:43 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Mon Mar 18, 11:58 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Tim E. Real, (Tue Mar 19, 12:31 am)
Re: [LAD] Mixing audio: Noiseless volume changes, James Morris, (Mon Mar 18, 11:28 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Mon Mar 18, 11:45 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Harry van Haaren, (Tue Mar 19, 2:09 am)
Re: [LAD] Mixing audio: Noiseless volume changes, Tim Goetze, (Tue Mar 19, 3:17 am)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Tue Mar 19, 1:02 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Tim Goetze, (Tue Mar 19, 1:53 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Tue Mar 19, 3:08 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Tim Goetze, (Tue Mar 19, 3:37 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Tue Mar 19, 4:31 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Tim Goetze, (Tue Mar 19, 7:06 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Charles Z Henry, (Tue Mar 19, 10:26 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Tue Mar 19, 10:57 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Charles Z Henry, (Tue Mar 19, 11:12 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Tue Mar 19, 11:30 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Fons Adriaensen, (Tue Mar 19, 10:26 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Harry van Haaren, (Tue Mar 19, 1:31 pm)
Re: [LAD] Mixing audio: Noiseless volume changes, Harry van Haaren, (Tue Mar 19, 4:30 am)
Re: [LAD] Mixing audio: Noiseless volume changes, Tim Goetze, (Tue Mar 19, 3:22 am)