Voice Processing Audio Unit Quality Settings

Q:  What are the differences between the quality values set with the kAUVoiceIOProperty_VoiceProcessingQuality property?

A: iOS 4 includes a new Voice Processing Audio Unit which provides significantly better audio quality and is specially designed for high-quality voice chatting. Two algorithms are now available allowing developers to fine tune the quality versus complexity (CPU usage) tradeoff.

The values between 0 - 63 use the standard suppression algorithm from iPhone OS 3 for lower CPU usage, while values between 64 - 127 use the high-quality echo canceler for superior echo rejection. The default value for this property is 127.

Listing 1  Setting the Voice Processor Quality.

OSStatus SetVoiceAUQuality(AudioUnit inVoiceUnit, UInt32 inQuality)

{

    if ((inVoiceUnit == NULL) || (inQuality > 127)) return paramErr;

    OSStatus result = AudioUnitSetProperty(inVoiceUnit, kAUVoiceIOProperty_VoiceProcessingQuality, kAudioUnitScope_Global, 1, &inQuality, sizeof(inQuality));

    if (result) NSLog(@"Error setting voice unit quality: %ld\n", result);

    return result;

}

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