My app inputs electrical waveforms from an IV485B39 2 channel USB device using an AVAudioSession. Before attempting to acquire data I make sure the input device is available as follows:
AVAudiosSession *audioSession = [AVAudioSession sharedInstance];
[audioSession setCategory :AVAudioSessionCategoryRecord error:&err];
NSArray *inputs = [audioSession availableInputs];
I have been using this code for about 10 years.
My app is scriptable so a user can acquire data from the IV485B29 multiple times with various parameter settings (sampling rates and sample duration). Recently the scripts have been failing to complete and what I have notice that when it fails the list of available inputs is missing the USBAudio input. While debugging I have noticed that when working properly the list of inputs includes both the internal microphone as well as the USBAudio device as shown below.
VIB_TimeSeriesViewController:***Available inputs = ( "<AVAudioSessionPortDescription: 0x11584c7d0, type = MicrophoneBuiltIn; name = iPad Microphone; UID = Built-In Microphone; selectedDataSource = Front>", "<AVAudioSessionPortDescription: 0x11584cae0, type = USBAudio; name = 485B39 200095708064650803073200616; UID = AppleUSBAudioEngine:Digiducer.com :485B39 200095708064650803073200616:000957 200095708064650803073200616:1; selectedDataSource = (null)>" )
But when it fails I only see the built in microphone.
VIB_TimeSeriesViewController:***Available inputs = ( "<AVAudioSessionPortDescription: 0x11584cef0, type = MicrophoneBuiltIn; name = iPad Microphone; UID = Built-In Microphone; selectedDataSource = Front>" )
If I only see the built in microphone I immediately repeat the three lines of code and most of the "inputs" contains both the internal microphone and the USBAudioDevice
AVAudiosSession *audioSession = [AVAudioSession sharedInstance];
[audioSession setCategory :AVAudioSessionCategoryRecord error:&err];
NSArray *inputs = [audioSession availableInputs];
This fix always works on my M2 iPadPro and my iPhone 14 but some of my customers have older devices and even with 3 tries they still get faults about 1 in 10 tries.
I rolled back my code to a released version from about 12 months ago where I know we never had this problem and compiled it against the current libraries and the problem still exists. I assume this is a problem caused by a change in the AVAudioSession framework libraries. I need to find a way to work around the issue or get the library fixed.