 | | | Various sound problems | Various sound problems 2004-01-22 - By Joakim Birgersson
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I have been wondering about clicks-on-volume-change for a while since I'm
getting clicks/cracking sounds in a hobby project I'm doing. I have read
that most software sound/music mixers (for example .MOD/.XM players) uses
volume ramping to avoid clicks on volume change.
I assume a "ramp" is a interpolation from a current volume/data-value to a
actual volume/data-value so it happens over time, avoiding quick changes (?)
I have a couple of question I hope someone has the knowledge and time to
answer.
1) What do you ramp, is it the volume (as in playing a sample at volume=90
and then a new at volume=10) or is it the byte/word data in the wave-form?
Say I'm playing a sample (signed 16-bit output) and stops it to play a new
sample. The last word in the first sample outputted was -32000 and the first
word in a new sample is +32000. Now, when I stop the first sample to play
the second sample there will be a 64000 jump in the value outputted.
The first sample play at volume=90 and the second at volume=10. There will
be a -80 volume jump.
What should I ramp? The volume from 90 to 10 or the word data from -32000 to
+32000?
2) How fast should one ramp? How quick can the volume/data change without
clicks? Is it hardware dependant and in that case, what is practical?
Regards,
Joackim
>From: Dietrich Epp <dietrich@(protected)>
>To: Mac Games Developers Developers <mac-games-dev@(protected)>
>Subject: Re: Various sound problems
>Date: Wed, 21 Jan 2004 20:47:05 -0800
>
>On Jan 20, 2004, at 9:02 PM, Ken Pajala wrote:
>
>>I'm having various problems with sounds and I'm wondering if anyone else
>>has
>>experienced these problems or has an idea of what I might be doing wrong.
>>I've asked on the QuickTime-api list as well, but with not much luck so
>>far...
>>
>>First: loading sounds from a file (aiff or mp3) causes iTunes to make
>>clicking/crackling noises. I'm basically using QuickTime (through
>>PutMovieIntoTypedHandle) to load the files. I filed a bug with Apple on
>>this
>>one a couple months ago.
>>
>>Second: playing a sound many times (around twice a second) eventually
>>makes
>>iTunes crackle as well. With this problem and the next one it doesn't
>>matter
>>if I'm playing a sound loaded from a resource or a file.
>>
>>Third: ramping the volume up or down using multiple calls to
>>SndDoImmediate
>>with volumeCmd causes the same crackling noise many times a second (with
>>or
>>without iTunes playing).
>
>Pardon the ASCII art.
>Sine wave:
> _ _
>/ \ / \
> \_/ \_/
>
>Sine wave with volume change:
>
> V
> _ _
> _ _| \ / \
>/ \ / | | |
> \_/ | |
> \_/
>
>Notice the jump underneath the 'arrow'... this is a loud 'pop'. According
>to the diagram's scale, this is an increase of only 3 dB, but the crackling
>noise is exactly as loud as the new, louder sound.
>
>As for the first and second problems, I have no idea what you're doing.
>iTunes is crackling? So iTunes is playing in the background, and your
>application loads a sound?
>
>Are you using double buffering to play your sounds?
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