iOS7 robotic/garbled in speaker mode on iPhone5s

Question

We have a VOIP application, that records and plays audio. As such, we are using PlayAndRecord (kAudioSessionCategory_PlayAndRecord) audio session category. So far, we have used it successfully with iPhone 4/4s/5 with both iOS 6 and iOS 7 where call audio and tones played clearly and were audible. However, with iPhone 5s, we observed that both the call audio and tones sound robotic/garbled in speaker mode. When using earpiece/bluetooth/headset, sound is clear and audible. iOS Version used with iPhone 5s: 7.0.4

We are using audiounits for recording/playing of call audio. When setting audio properties like session category, audio route, session mode etc., we tried both the older (deprecated) AudioSessionSetProperty() and AVAudioSession APIs. For playing tones, we are using AVAudioPlayer. Playing of tones during the VOIP call and also when pressing keypad controller within the app produces robotic sound. When instantiating the audio component using AudioComponentInstanceNew, we set componentSubType to kAudioUnitSubType_VoiceProcessingIO. When replacing kAudioUnitSubType_VoiceProcessingIO with kAudioUnitSubType_RemoteIO, we noticed that the sound of call audio and tones was no longer robotic, it was quite clear, but the volume level was very low when using speaker mode.

In summary, keeping all the other audio APIs the same:

kAudioUnitSubType_VoiceProcessingIO: Volume is high (desirable) but sound of tones and call audio was robotic in speaker mode. kAudioUnitSubType_RemoteIO: Sound of tones and call audio was clear but it is not audible.

STEPS TO REPRODUCE - Set audio session category to playAndRecord. - Set audio route to speaker - Set all the other audio properties like starting audio unit, activating the audio session, instantiating the audio components. - Set the input and render callbacks - Try both options 1. Play tones using AVAudioPlayer 2. Play call audio

Any suggestions on how to get over this issue. Raised as an issue with Apple but no response yet from them.

i have shared the code here github link

Answer 1

The only difference between kAudioUnitSubType_VoiceProcessingIO and kAudioUnitSubType_RemoteIO is that voiceProcessing includes code to tune out acoustic echo i.e. tunes out the noise from the speaker so the microphone doesn't pick it up. Its been a long time since I've played with the audio framework but I remember that to sound off there could be any number of things,

1. Are you doing any work in the audio callbacks that could be taking a long time?

   The callbacks run on realtime threads. if your processing takes too long you can miss data. Would be helpful to track the data over a fixed period of time to see are you capturing it all. Use something like wireShark to sniff the network. Record the number of packets and see did the phone capture the same.

2. Are you modifying any of the audio?
3. Do you have a circular buffer that might be causing an issue?

I've had several issues doing this and one was using a third party circular buffer that was described as low latency and efficient ... it wasn't. I answered my own question here and included my circular buffer implementation that greatly improved my audio as the issue was I was skipping data.

Give this a go and let me know: iOS UI are causing a glitch in my audio stream

Please be aware that some of this code is unique to the audio format ALaw, 0xD5 is a byte of silence in ALaw, if you are using linear PCM or any other that will probably be a noise of some kind.