[PD] prevent dac~ from output damage

IOhannes m zmoelnig zmoelnig at iem.at
Fri Oct 5 15:24:48 CEST 2007

Olivier Revollat wrote:
> I have read that in pure data if you mess with audio signal it can
> destoy your audio hardware (and even your ears !!) because the signal is
> not bound to -1/+1 so I wonder if there is any  simple tip, abstract,
> external that handle dac~ and protect from hardware damage ?

i don't know where you have heard that...

the simplest one is: play at low volumes.
you can destroy your PA and permanently damage the ears of a large
audience with something as simple as the apple startup sound. no pd

Pd internally does not clip the signal to -1..+1, when it comes to the
[dac~] the audio-API used usually will clip it, so that +-1 is "fullscale".
so in practice this is not a real problem. (well, since the signal is
digitally clipped, you well get a lot of high harmonics; this might be a
problem with your tweeters; but this is not a problem because Pd uses
signal-values that are not bound to a small range, but because the
audio-api have this boundary)

what could be a problem is, if you have high DC proportion in your
signal. speakers usually do not like DC.
this is only a problem if your D/A-converters actually output an
analogue DC if they get a digital offset. a lot of D/A converters don't.
however, to be on the safe side you should use a high-pass filter to
filter out any DC offsets, either within Pd (just put a [hip~ 5] before
the [dac~]) or in your analogue mixing console (just switch on the
rumble filter)

but of course this is no problem to Pd, you have this with any software
that can playback sounds.


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