[chuck-users] Filters blowing up: any news?

Kassen signal.automatique at gmail.com
Tue Feb 16 17:03:18 EST 2010

2010/2/16 Stefan Blixt <stefan.blixt at gmail.com>

> If you do SinOsc s=> dac and the 100.0 => s.gain, are you then able to blow
> a speaker on a Mac laptop even if it's main volume is turned down? That's
> the curious thing to me, how the filter messes up so badly it makes my
> MacBook's speaker scream even though the volume is almost down to zero.
100? Try something like this value for a output; 242210436022272.0
That's a actual recorded output of .last(). I'm not sure what would happen
if something of that volume would be played back on real speakers; there is
probably a UN convention against that kind of thing ;-).

>From what I understand of the situation you wouldn't blow the speaker. If
Apple was smart they put in a pre-amp that's slightly smaller than the
maximum load of the speaker yet slightly over-speced for the output of the
dac to keep repairs down. But yes; apparently you will can get a very high
volume even though the (software) fader is down.

This is what we know.

Then from that I speculated (and unless something more credible comes by I
think it's a good theory) that Apple is doing everything in float (with
virtually unlimited headroom for practical applications), setting the master
volume with a floating point multiplication, and handing the resultant value
to the dac where inevitably it will be turned into a plain integer. In this
case that integer will be the highest volume the poor little dac can take.
If that's not it I can't imagine why +/- some 15 digit number would have a
higher amplitude than +/-1, as a final output, post master fader.

This is cheap compared to tweaking the voltage on the final hardware amp
(which would always preserve the full bit-range) and probably sounds a lot
better than going integer and throwing away a lot of bits at low volume, but
it fails to take into account that we may not just turn the volume down for
a more pleasant listen but also to protect our ears. Combine that with with
potentially very sensitive studio or DJ headphones and you have a situation
that may lead to hearing damage. I know that my own pro DJ headphones will
output a lot more volume than my mid-range earbuds at the same volume
setting for a headphone jack.

IMHO this would be a oversight by Apple and I'm a bit surprised there hasn't
been a storm of practical joke mails aimed at OSX users featuring videoclips
embedding floating-point audio. I'd offer at least a optional output limiter
like what has been proposed for mp3 players. I don't believe in those
for protecting children's ears through mandatory regulation because of the
differences in headphone output volume, but for user-set protection it might
be a good idea. Of course ChucK is a bit more likely to cause this sort of
issue than the average off-the-shelf audio player.

Here is the original topic if you'd like to try to reproduce the findings so
far; http://electro-music.com/forum/viewtopic.php?t=37921

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