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I have a windows phone 8 app which plays audio streams from a remote location or local files using the BackgroundAudioPlayer. I now want to be able to add audio effects, for example, reverb or echo, etc...

Please could you advise me on how to do this? I haven't been able to find a way of hooking extra audio processing code into the pipeline of audio processing even through I've read much about WASAPI, XAudio2 and looked at many code examples.

Note that the app is written in C# but, from my previous experience with writing audio processing code, I know that I should be writing the audio code in native C++. Roughly speaking, I need to find a point at which there is an audio buffer containing raw PCM data which I can use as an input for my audio processing code which will then write either back to the same buffer or to another buffer which is read by the next stage of audio processing. There need to be ways of synchronizing what happens in my code with the rest of the phone's audio processing mechanisms and, of course, the process needs to be very fast so as not to cause audio glitches. Or something like that; I'm used to how VST works, not how such things might work in the Windows Phone world.

Looking forward to seeing what you suggest...

Kind regards,

Matt Daley

Matt Daley
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I need to find a point at which there is an audio buffer containing raw PCM data

AFAIK there's no such point. This MSDN page hints that audio/video decoding is performed not by the OS, but by the Qualcomm chip itself.

You can use something like Mp3Sharp for decoding. This way the mp3 will be decoded on the CPU by your managed code, you can interfere / process however you like, then feed the PCM into the media stream source. Main downside - battery life: the hardware-provided codecs should be much more power-efficient.

Soonts
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  • Yes, I think you're right there. I should have worked that out myself! So, if the mp3 decoding happens in hardware on the snapdragon CPU, I wonder whether software can access the audio stream that comes out before it goes into the audio output stage. On my Nokia Lumia phone there is a graphic equalizer/audio processor but I don't know whether that processing happens in software or in hardware on the chip? Alternatively, perhaps one can program the DSP, although where to find out about that... – Matt Daley Jan 16 '14 at 10:41
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    Well maybe this provides clues to programming the DSP on a snapdragon: [link](http://en.wikipedia.org/wiki/Qualcomm_Hexagon) but I expect only for partners/device manufacturers. – Matt Daley Jan 16 '14 at 10:45