[PD] headroom in Pd

[Martin Peach]

On 2013-12-29 10:08, Alexandre Torres Porres wrote:
> here's the deal, if I have a square wave in Pd running at 1 -1 peak to
> peak, then you say that should be my maximum output, right?
>
> Thing is that if I give it an extra boost (say, multiply it by 2) I
> can clearly listen an increase in loudness. Hence, something in my
> system is allowing some headroom to be output.
>
> I got a macbook air from 2010 running 10.7.5... if Pd is not
> responsible for this, maybe my hardware + Mac OS is?
>

Yes it's a Mac-specific issue. On Win7 I get no difference above 1.0.
The Apple audio driver is responsible for "clipping" values outside of 
[-1.0..1.0] as they arrive from possibly multiple applications. The docs 
state that clipping can be done in a "soft" way, so I suspect that the 
default driver (for the headphone output) is doing some sort of 
compression. Possibly if you use an external interface this won't happen 
(?).

(see for example 
https://developer.apple.com/library/mac/documentation/DeviceDrivers/Conceptual/WritingAudioDrivers/ImplementDriver/ImplementDriver.html#//apple_ref/doc/uid/TP30000732-BAJCBIAF
)
Martin


> here's the patch, try yourselves and tell me what you get please.
>
> Cheers
>
>
> #N canvas 653 26 257 182 10;
> #X obj 79 97 dac~;
> #X obj 85 41 square~ 440;
> #X floatatom 125 72 5 0 0 0 - - -;
> #X obj 85 70 *~;
> #X connect 1 0 3 0;
> #X connect 2 0 3 1;
> #X connect 3 0 0 0;
> #X connect 3 0 0 1;
>
> 2013/12/21, IOhannes m zmölnig <zmoelnig at iem.at>:
>> On 2013-12-21 14:58, peiman khosravi wrote:
>>> However, it's probably wise to clip the signal before sending it to dac~.
>>> Entirely for health and safety reasons!
>>
>> this really depends...a clipping sine will have loads of high
>> frequencies that might be equally damaging to your audience.
>>
>> if you want to be safe, use math to make sure that your signal won't
>> exceed -1..+1 before sending to the [dac~].
>>
>> or use a limiter (zexy has a handy one).
>>
>> fgmrdsa
>> IOhannes
>>
>>
>
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