Hi,
I know this is probably a long-shot, let me explain my situation.
I’m the developer of AudioTools, over 10 years on the app store, lots of audio
test & measurement functions. One in particular is a 5.1 surround signal
generator, which works with our own hardware device, iAudioInterface2, which
happens to have a Toslink digital audio output connector. The idea is that I
pre-encode surround signal audio files in the Dolby Digital 5.1 format, open
the file in the app, and break the data into packets that get formatted to
Dolby specs and sent out the Toslink connector at 48k sample rate.
Surprisingly, this actually works. For many years it has, anyway. I can send
out a pink noise signal to a particular channel, or send an encoded music file
out to the system. I am using basic remote IO audio processing here. Despite
many years in audio and DSP I do not consider myself an iOS guru, I just use a
simple set of iOS tools that seem to work.
Starting with iOS 13 however, the surround signal generator no longer works.
This scheme relies on the signal (data) not being altered by iOS at all, it
must be sent through unaltered, as bit-accurate audio. In 13, I get just random
noise, while the same app on iOS 11 or 12 outputs the surround data correctly.
My guess is that Apple has inserted a sample rate converter, even though as far
as I can tell the hardware is still running at 48k, and I am requesting 48k.
I’ve posted a bug report to Apple but unsurprisingly I’ve had no response to it
since I am likely the only person on Earth who cares about this. Any ideas on
something to try or if perhaps anyone else has knowledge about this I would
highly appreciate it!
Best,
Andrew Smith
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