[PD] prevent dac~ from output damage

[IOhannes m zmoelnig]

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
involved.


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.


mfga.er
IOhannes