CODEWITHSUNDEEP
iosxcodecore-audioaudiounit
Spinoxa
Spinoxa

Reputation: 657

Audio Unit recording: increased volume of buffers

I am building an audio recording app for iPhone in which I use remote audio units. After performing some audio analysis on incoming buffers I write the buffers to disk using:

ExtAudioFileWriteAsync

However, the problem I have is that the recorded buffers are quieter than I would like.

I would like to increase the volume of the buffers by manually multiplying them by a volume factor just prior to writing to disk. Can anyone please explain to me the best way to do this?

(For various reasons, a manual adjustment at the final stage is more attractive than changing any of the audio unit properties, which otherwise work well for my application.)

Thanks in advance!!

Upvotes: 3

Views: 3673

Answers (2)

sbooth
sbooth

Reputation: 16966

You can use Accelerate.framework to do this quickly and easily. Since you are using AudioUnits I assume you have deinterleaved float buffers so something like this should work:

float desiredGain = 1.06f; // or whatever linear gain you'd like
AudioBufferList *ioData; // audio from somewhere
for(UInt32 bufferIndex = 0; bufferIndex < ioData->mNumberBuffers; ++bufferIndex) {
  float *rawBuffer = (float *)ioData->mBuffers[bufferIndex].mData;
  vDSP_Length frameCount = ioData->mBuffers[bufferIndex].mDataByteSize / sizeof(float); // if you don't have it already
  vDSP_vsmul(rawBuffer, 1, &desiredGain, rawBuffer, 1, frameCount);
}

Upvotes: 8

Nik Reiman
Nik Reiman

Reputation: 40380

You might be over thinking this problem. :-) You just need to loop over the values in your buffer and multiply each one by the desired gain factor.

Upvotes: 0

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