From what I have observed, downsampling or upsampling is automatic, if you use a mixer. Specifically what I observed was that one end of the mixer is attached to the input node, which was running at 44.1KHz. The other end of the mixer was connected to an AVAudioPlayerNode running at 48KHz. I could hear the network transmitted audio coming out of the speaker. This confused me at first until I looked at the specific documentation for AVAudioMixer: "The mixer accepts input at any sample rate and efficiently combines sample rate conversions. It also accepts any channel count and correctly upmixes or downmixes to the output channel count."

The call to setVoiceProcessingEnabled(isEnabled: Bool) is synchronous, it triggers a configuration change in the engine, so you must ensure that you access formats from input and output node after changing the voice processing enabled state to ensure you’re configuring your graph with the correct formats. Additionally there is some sample code available here as part of the AVEchoTouch project - https://developer.apple.com/documentation/avfaudio/using-voice-processing?language=objc

I've gotten OK, Bad-Gateway, Gateway Time-Out on four different systems. Even when OK is returned, it takes a while to get a response. This started almost exactly at 10am pacific time for me. Like many of you I used the security command line to check my certs, checked my firewall (PFSense), and even switch my build system and my target iPad to use my iPhone personal hot-spot, in order to bypass my infrastructure and still, no-joy. After reading your posts, I have become convinced that this is an Apple services issue, even though their status page says everything is working. More information. I have another project (Project-B) I'm working on, which is being developed on a different machine. Project-B installs on the same target iPad with no issues. I migrated the failing project (Project-A) over to this machine and added the missing certificates to the keychain so that the failing project would build. Even on this second system, I'm consistently getting the error for project-a but not for project-b. So, apparently this failure is specific to the type of certificate or provisioning for the target app, it seams. Project-A: Hardware app using DriverKit, custom USB hardware, microphone, camera, etc. Only viable on iPadOS with an M-Processor. Project-B: SwiftUI, SwiftData, document-based. Does use a FLIR camera but does not require DriverKit. Also uses microphone and camera. Are any of you using DriverKit or working with anything that corresponds to Project-A? Have you tried build a simple sample app that does nothing special; does it work?

Quinn, I met you face-to-face back in 2005. Glad you are still around.