Yikes! Well, the purpose of my project was to investigate the possibilities of using OpenAI's realtime API on Apple tech, and I'm indeed discovering the gotchas.
So, IIUC: - on macOS I can get beneath the AudioUnit level and go straight to AudioDevice; down to the wire, so to speak. And roll my own AEC & VAD. Alternatively I can use VoiceProcessingIO AudioUnit which gives me AEC & VAD tho' they don't play nice together, but if I roll my own VAD (using the WebRTC code) I'm good to go. - on iOS I can't get at the AudioDevice, but still have the VoiceProcessingIO technique available as above. Alternatively I could use RemoteIO AudioUnit and roll my own AEC+VAD. But then I'm not getting system audio-out. hum ho. liveable-withable. - on WatchOS, we don't have AudioDevice OR VoiceProcessingIO audioUnit, but we DO still have RemoteIO audiounit. So if I want something that works on all 3, I kinda need to roll my own AEC+VAD. I'm struggling really hard to extract aec3 out of WebRTC. Whereas VAD was pretty straight forward, aec3 seems to have a dependency on something called abseil. It seems AEC is far from a "Solved Problem". I see https://www.microsoft.com/en-us/research/academic-program/acoustic-echo-cancellation-challenge-icassp-2023/ Microsoft have recently (2023) issued a challenge inviting novel AEC solutions (presumably the current AI boom is gona shake loose some new approaches), but as an outsider I don't get to see the submissions. e.g. the winning non-microsoft entry is behind a paywall https://ieeexplore.ieee.org/document/10096411 (though maybe the same as https://arxiv.org/pdf/2303.06828). I wonder whether "cheating" buys much; i.e. emitting a periodic sweep/chirp from the speakers to estimate the impulse-response of the acoustic environment, in order to deduce an inverse-IR. Then I think the AEC is just applying that, possibly together with some delay to compensate for I/O latency. Does anyone have an intuition whether it's even sensible to be considering realtime AEC on WatchOS? Just from a performance PoV it might rinse out the battery really fast. π On Fri, 18 Oct 2024 at 11:55, Tamás Zahola via Coreaudio-api < coreaudio-api@lists.apple.com> wrote: > Hold on a sec, how are you planning to use the AudioDevice VAD on watchOS? > It is a macOS-only API. It's not available on watchOS, neither on iOS. > > Now, considering what Julian wrote, I think your problem might he that > you're using the VPIO unit in conjunction with the AudioDevice VAD. Because > if what Julian wrote is true, that AudioDevice already has echo > cancellation when VAD is enabled, then what could be happening is that your > output signal is subtracted *twice* from the input: first by the echo > canceller of AudioDevice, and then by the VPIO unit. So in effect the VPIO > unit ends up re-adding the echo with inverted phase. > > I would recommend trying just AudioDevice directlt, without the VPIO unit. > > Obviously, this is all macOS-only. On iOS (and I guess watchOS) you only > have AudioUnits, so you must use your own VAD. > > Regards, > Tamás Zahola > > On 2024. Oct 18., at 12:30, π via Coreaudio-api < > coreaudio-api@lists.apple.com> wrote: > > > Thanks for the pointer Tamás! > > Pulling out VAD from WebRTC worked a treat. > > I started with https://github.com/daanzu/py-webrtcvad-wheels and knocked > together a hello.cpp and CMakeLists.txt ( > https://gist.github.com/p-i-/598da13d2a1a1e2a6ec978e15fa7d892) > > I have to say, it feels hella awkward that I cannot control the pipeline > and use native AudioUnits for this kind of work. > > Surely it is a mistake on Apple's part to put VAD before AEC, if this is > really what they're doing... it's gona trigger VAD callback on > incoming/remote audio, rather than user-speech. > > For a low-power usage scenario (say WatchOS), I really want to be > dynamically rerouting -- if there's no audio being sent thru the speaker, I > don't want AEC eating CPU cycles, but I DO want VAD detecting user-speech > onset. And if audio IS being sent thru the speaker, I want AEC to be > subtracting it, and VAD to be operating on this "cleaned" mic-input. I'd > love it if VoiceProcessingIO unit took care of all of this. > > I haven't yet managed to scientifically determine exactly what > VoiceProcessingIO unit is actually doing, but if I engage its AEC and VAD > and play a sine-wave, it disturbs the VAD callbacks, yet successfully > subtracts the sinewave from mic-audio. So I strongly suspect they have > these two subcomponents wired up in the wrong order. > > If this is indeed the case, is there any liklihood of a future fix? Do > Apple core-audio devs listen in on this list? > > π > > On Thu, 17 Oct 2024 at 10:24, Tamás Zahola via Coreaudio-api < > coreaudio-api@lists.apple.com> wrote: > >> You can extract the VAD algorithm from WebRTC by starting at this file: >> https://chromium.googlesource.com/external/webrtc/stable/src/+/master/common_audio/vad/vad_core.h >> >> You'll also need some stuff from the common_audio/signal_processing >> folder, but otherwise it's self-contained. >> >> It's easy for me to get the audio-output-stream for MY app (it just comes >> in over the websocket), but I may wish to toggle whether I want my AEC to >> be cancelling out any output-audio generated by other processes on my mac. >> >> >> From macOS Ventura onwards it is possible to capture system audio with >> the ScreenCaptureKit framework, although your app will need extra privacy >> permissions. >> >> It must be possible on macOS, as apps like soundFlower or blackHole are >> able to do it. >> >> >> BlackHole and SoundFlower are using an older technique, where they >> install a virtual loopback audio device on the system (you can see it >> listed in Audio MIDI Settings as e.g. "BlackHole 2 ch"), and change the >> system's default output device to that, then capture from the input port of >> this loopback device. But this requires installing the virtual device >> in /Library/Audio/Plug-Ins/HAL, which requires admin privileges. >> >> But mobile, I'm not so sure. My memory of iPhone audio dev (~2008) is >> that it was impossible to access this. But there's now some mention of v3 >> audio-units being able to process inter-app audio. >> >> >> On iOS you must use the voice-processing I/O unit. Normal apps cannot >> capture the system audio output. Technically there is a way to do it with >> the ReplayKit framework, but it's a pain in the ass to use, and the primary >> purpose of that framework is capturing screen content, not audio. If you >> try e.g. Facebook Messenger on iOS, and initiate screen-sharing in a video >> call, that's going to use ReplayKit. >> >> Regards, >> Tamás Zahola >> >> On 17 Oct 2024, at 08:04, π via Coreaudio-api < >> coreaudio-api@lists.apple.com> wrote: >> >> Thankyou for the replies. I am glad to see that this mailing-list is >> still alive, despite the dwindling traffic this last few years. >> >> Can I not encapsulate a VPIO unit, and control the input/output >> audio-streams by implementing input/render callbacks, or making connections? >> >> I'm veering towards this approach of manual implementation: Just to use a >> (misnamed as it's I/O) HALInput unit on macOS or a RemoteIO unit on the >> mobile platforms to access the raw I/O buffers, and write my own pipeline. >> >> Would it be a good idea to use https://github.com/apple/AudioUnitSDK to >> wrap this? My hunch is to minimize the layers/complexity and NOT use this >> framework. >> >> And for the AEC/VAD, can anyone offer a perspective? Arshia? The two >> obvious candidates I see are WebRTC and SpeeX. GPT4o reckons WebRTC will be >> the most-advanced / best-performant solution, with the downside that it's a >> big project (and maybe a more complicated build process), while SpeeX is >> more light-weight and will probably do the job well enough for my purposes. >> >> And as both are open-source, I may have the option of pulling out the >> minimal-dependency files and building just those. >> >> The last question is regarding system-wide audio output. It's easy for me >> to get the audio-output-stream for MY app (it just comes in over the >> websocket), but I may wish to toggle whether I want my AEC to be cancelling >> out any output-audio generated by other processes on my mac. e.g. if I am >> watching a YouTube video, maybe I want my AI to listen to that, and maybe I >> want it subtracted. So do I have the option to listen to SYSTEM-level audio >> output (so as to feed it into my AEC impl)? It must be possible on macOS, >> as apps like soundFlower or blackHole are able to do it. But mobile, I'm >> not so sure. My memory of iPhone audio dev (~2008) is that it was >> impossible to access this. But there's now some mention of v3 audio-units >> being able to process inter-app audio. >> >> π >> >> On Wed, 16 Oct 2024 at 19:35, Arshia Cont via Coreaudio-api < >> coreaudio-api@lists.apple.com> wrote: >> >>> Hi π, >>> >>> From my experience that’s not possible. VPIO is an option for the lower >>> level IO device; so is VAD. You don’t have much control over their >>> internals, routing and wirings! Also, from our experience, VPIO has >>> different behaviour on different devices. On some iPads we saw “gating” >>> instead of actually removing echo (be aware of that!). In the end for a >>> similar use-case we ended up doing our own AEC and Activity Detection. >>> >>> Cheers, >>> >>> Arshia Cont >>> metronautapp.com >>> >>> >>> >>> On 15 Oct 2024, at 18:08, π via Coreaudio-api < >>> coreaudio-api@lists.apple.com> wrote: >>> >>> Dear Audio Engineers, >>> >>> I'm writing an app to interact with OpenAI's 'realtime' API >>> (bidirectional realtime audio over websocket with AI serverside). >>> >>> To do this, I need to be careful that the AI-speak doesn't make its way >>> out of the speakers, back in thru the mic, and back to their server (else >>> it starts to talk to itself, and gets very confused). >>> >>> So I need AEC, which I've actually got working, >>> using kAudioUnitSubType_VoiceProcessingIO >>> and AudioUnitSetProperty(kAUVoiceIOProperty_BypassVoiceProcessing, setting >>> to False). >>> >>> Now I also wish to detect when the speaker (me) is speaking or not >>> speaking, which I've also managed to do >>> via kAudioDevicePropertyVoiceActivityDetectionEnable. >>> >>> But getting them to play together is another matter, and I'm struggling >>> hard here. >>> >>> I've rigged up a simple test ( >>> https://gist.github.com/p-i-/d262e492073d20338e8fcf9273a355b4), where a >>> 440Hz sinewave is generated in the render-callback, and mic-input is >>> recorded to file in the input-callback. >>> >>> So the AEC works delightfully, subtracting the sinewave and recording my >>> voice. >>> And if I turn the sine-wave amplitude down to 0, the VAD correctly >>> triggers the speech-started and speech-stopped events. >>> >>> But if I turn up the sine-wave, it messes up the VAD. >>> >>> Presumably the VAD is working over the pre-EchoCancelled audio, which is >>> most undesirable. >>> >>> How can I progress here? >>> >>> My thought was to create an audio pipeline, using AUGraph, but my >>> efforts have thus far been unsuccessful, and I lack confidence that I'm >>> even pushing in the right direction. >>> >>> My thought was to have an IO unit that interfaces with the hardware >>> (mic/spkr), which plugs into an AEC unit, which plugs into a VAD unit. >>> >>> But I can't see how to set this up. >>> >>> On iOS there's a RemoteIO unit to deal with the hardware, but I can't >>> see any such unit on macOS. It seems the VoiceProcessing unit wants to do >>> that itself. >>> >>> And then I wonder: Could I make a second VoiceProcessing unit, and have >>> vp1_aec split send its bus[1(mic)].outputScope to vp2_vad.bus[1].inputScope? >>> >>> Can I do this kind of work by routing audio, or do I need to get my >>> hands dirty with input/render callbacks? >>> >>> It feels like I'm going hard against the grain if I am faffing with >>> these callbacks. >>> >>> If there's anyone out there that would care to offer me some guidance >>> here, I am most grateful! >>> >>> π >>> >>> PS Is it not a serious problem that VAD can't operate on post-AEC input? >>> _______________________________________________ >>> Do not post admin requests to the list. 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