linuxaudio.org

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On Mon, Mar 18, 2013 at 5:50 PM, Tim E. Real  wrote:
> Hi again. Looking for any advice, tips, tricks, anecdotes etc.

quoted text
>

> I want to eliminate or reduce 'zipper' noise on volume changes.

> So I'm looking at two techniques:

> Zero-crossing / zero-value signal detection, and slew-rate limiting.

> Code is almost done, almost ready to start testing each technique.

> Each technique has some advantages and disadvantages.

>

> If I use a slew-rate limiter, I figure for a sudden volume factor change

>  from 0.0 to 1.0, if I limit the slew rate to say 0.01 per sample then

> after

>  100 samples the ramp will be done.

> But even with a fine ramp, this still might introduce artifacts in the

> audio.

>

You cannot avoid artifacts in the audio. The only question is what is the

nature of the artifacts.
> If I use a zero-crossing/zero-value detector and apply volume changes

quoted text
>

Zero crossing stuff is a completely bogus idea that needs to be eliminated

from the lexicon of audio software. You will not be accomplishing anything

trying to use such a technique, other than introduce even more artifacts

(and rather horrendous ones at that). Even zero-valued samples are not

particularly useful - keep in mind that what defines transducer (read:

speaker) behaviour is power, not instantaneous volume.
Just use sensibly short ramped changes. For the record, Ardour uses 64 or a

JACK period size, whichever is, hmm, larger or smaller, can't recall.
--p
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On Mon, Mar 18, 2013 at 5:50 PM, Tim E. =

Real <termtech@rogers.com> wrote:

Hi again. Looking for any advice, tips, tricks, anecdotes etc.
I want to eliminate or reduce 'zipper' noise on volume changes.

So I'm looking at two techniques:

Zero-crossing / zero-value signal detection, and slew-rate limiting.

Code is almost done, almost ready to start testing each technique.

Each technique has some advantages and disadvantages.
If I use a slew-rate limiter, I figure for a sudden volume factor change

=A0from 0.0 to 1.0, if I limit the slew rate to say 0.01 per sample then af=

ter

=A0100 samples the ramp will be done.

But even with a fine ramp, this still might introduce artifacts in the audi=

o.You cannot avoid artifacts in the audio. The on=

ly question is what is the nature of the artifacts. =A0=A0
If I use a zero-crossing/zero-value detector and apply volume changesZero crossing stuff is a completely bogus idea that nee=

ds to be eliminated from the lexicon of audio software. You will not be acc=

omplishing anything trying to use such a technique, other than introduce ev=

en more artifacts (and rather horrendous ones at that). Even zero-valued sa=

mples are not particularly useful - keep in mind that what defines transduc=

er (read: speaker) behaviour is power, not instantaneous volume.=A0

Just use sensibly short ramped changes. For the record, Ardour uses 64 =

or a JACK period size, whichever is, hmm, larger or smaller, can't reca=

ll.--p
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