[linux-audio-dev] live pa questions

Pieter Palmers pieterp at joow.be
Mon Apr 4 18:24:27 UTC 2005

Andres Cabrera wrote:

>>Overheating of the amp is nonsense. Most amplifiers operate in class A 
>>or AB anyway, and maybe in class D. Heat dissipation is independant of 
>>the input signal for these amps. The types that might build up a problem 
>>with heat (e.g. class H) aren't used in PA enviroments. And before the 
>>amp overheats, your speakers will be dead.
>Thanks for clarifying. I remembered I heard about overheating somewhere
>with DC, and thought it was on the amp.
>Adding a small DC offset is one easy way of getting rid of denormal
>problems (in programs like csound and pd), do you know if this small DC
>offset is able to produce these effects?
I don't know about the output stage of a soundcard. (Almost) every 
soundcard uses a delta-sigma DAC, which needs some sort of low pass 
filtering. It needs an output buffer to transform the rather high 
impedance of this filter to a low output impedance, so the question is 
if there is some sort of DC decoupling impemented in this buffer. I 
don't know, but using a voltmeter (or scope) while applying a DC signal 
to the card will answer that.
if you take a look at the specs of the EMU1820M it states "Frequency 
Response: 0.0/-.35dB, 20Hz - 20kHz" which would mean that it doesn't 
output DC signals.

But as far as I know, most audio input stages are capacitively coupled, 
thereby removing such DC offsets, so there is little chance that this 
type of signals will propagate through the entire signal chain.



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