Question

I work for an audio recorder app and would like to add gain control but I don’t know how to do it. I have access to audio buffer but I don’t know how to make the sound louder or slower.
I see another apps that have a seekBar for selecting the decibels from a specific range.

aRecorder.read(buffer, 0, buffer.length);
fWriter.write(buffer); // Write buffer to file

Please tell me what should I do to implement gain control in my app.

Thanks.

Answer 1

Changing the volume is simple, just multiply all the samples by some fraction. A change of +/- 3dB (decibels) corresponds to multiplication by 2 or 0.5 respectively (see http://en.wikipedia.org/wiki/Decibel). To prevent discontinuities in the output, make sure that you vary the multiplication factor smoothly from beginning to end.

See AudioSampleBuffer::applyGainRamp() @ http://www.rawmaterialsoftware.com/api/classAudioSampleBuffer.html