[LAD] Regarding amplifying a PCM frame

Jörn Nettingsmeier nettings at folkwang-hochschule.de
Mon Oct 26 09:08:20 UTC 2009

On 10/26/2009 07:33 AM, Drip Stone wrote:
> Hi everybody,
> I have a question regarding amplifying a PCM frame. For each frame, I
> get a float number, and multiply this number by 2, and then output
> frames to alsa one by one using function snd_pcm_writei. But the wav
> file sounds the same to me, nothing gets amplified. Could anyone explain
> this to me? I appreciate your help!

you should hear an amplification by roughly 6dB... what might happen is 
this: your file already has a peak at 1.0f. after your operation, it 
will peak at 2.0f, which your DAC can't handle. so the file will have to 
be clamped between -1.0f and 1.0f, effectively undoing your gain 
operation. just a guess.

or you might be expecting the wrong thing... times two doesn't feel 
"twice as loud". then again, +6dB is quite audible in any case.

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