Write Int16 Into AVAudioPCMBuffer swift - ios

Question

I have a Data object in swift that is an array of Int16 objects. For some reason using ".pcmFormatInt16" did not work for the format of my AVAudioPCMBuffer and yielded no sound, or a memory error. Eventually, I was able to get white noise/static to play from the speakers by converting the Int16 to a float and putting that onto both channels of my AVAudioPCMBuffer. I have a feeling that I am getting close to the answer, because whenever I speak into the microphone I hear a different frequency of static. I think the issue is that I am not converting the converted Int16 into the buffer floatChannelData.
Here is my code:
for ch in 0..<2 {
for i in 0..<audio.count {
var val = Float( Int16(audio[i]) ) / Float(Int16.max)
if( val > 1 ){
val = 1;
}
if( val < -1 ){
val = -1;
}
self.buffer.floatChannelData![ch][i+self.bufferCount] = val
self.bufferCount+=1
}
}
self.audioFilePlayer.scheduleBuffer(self.buffer, at:nil, options: .interruptsAtLoop, completionHandler: {
print("played sum")
self.bufferCount=0
})

Answer 1

a typical multi-channel PCM buffer has the channels interleaving on a per sample basis although, not being familiar with swift audio, I find it refreshing to see here channels given a dimension on the buffer datastructure
... a flag goes up when I see your guard checks clamping val > 1 set to val = 1 etc. ... elsewhere that is not needed as those boundary checks are moot as the data nicely falls into place as is
... my guess is your input audio[] is signed int 16 because of your val > 1 and val < -1 ? if true then dividing by max int float is wrong as you would be loosing half your dynamic range ...
I suggest you look closely at your
var val = Float( Int16(audio[i]) ) / Float(Int16.max)
lets examine range of your ints in audio[]
2^16 == 65536 // if unsigned then values range from 0 to (2^16 - 1) which is 0 to 65535
2^15 == 32768 // if signed then values would range from -32768 to (2^15 - 1) which is -32768 to 32767
Please tell is whether input buffer audio[] is signed or not ... sometimes its helpful to identify the max_seen and min_seen values of your input data ... do this and tell us the value of max and min of your input audio[]
Now lets focus on your desired output buffer self.buffer.floatChannelData ... since you are saying its 16 bit float ... what is the valid range here ? -1 < valid_value < 1 ?
We can continue once you tell us answers to these basic questions