CODEWITHSUNDEEP
audiowin-universal-app
Niccolo Sacchi
Niccolo Sacchi

Reputation: 51

How to get amplitude of an audio stream in an AudioGraph to build a SoundWave using Universal Windows?

I want to built a SoundWave sampling an audio stream.

I read that a good method is to get amplitude of the audio stream and represent it with a Polygon. But, suppose we have and AudioGraph with just a DeviceInputNode and a FileOutpuNode (a simple recorder).

  1. How can I get the amplitude from a node of the AudioGraph?

  2. What is the best way to periodize this sampling? Is a DispatcherTimer good enough?

Any help will be appreciated.

Upvotes: 0

Views: 577

Answers (1)

andymule
andymule

Reputation: 382

First, everything you care about is kind of here: uwp AudioGraph audio processing

But since you have a different starting point, I'll explain some more core things.

An AudioGraph node is already periodized for you -- it's generally how audio works. I think Win10 defaults to periods of 10ms and/or 20ms, but this can be set (theoretically) via the AudioGraphSettings.DesiredSamplesPerQuantum setting, with the AudioGraphSettings.QuantumSizeSelectionMode = QuantumSizeSelectionMode.ClosestToDesired; I believe the success of this functionality actually depends on your audio hardware and not the OS specifically. My PC can only do 480 and 960. This number is how many samples of the audio signal to accumulate per channel (mono is one channel, stereo is two channels, etc...), and this number will also set the callback timing as a by-product.

Win10 and most devices default to 48000Hz sample rate, which means they are measuring/output data that many times per second. So with my QuantumSize of 480 for every frame of audio, i am getting 48000/480 or 100 frames every second, which means i'm getting them every 10 milliseconds by default. If you set your quantum to 960 samples per frame, you would get 50 frames every second, or a frame every 20ms.

To get a callback into that frame of audio every quantum, you need to register an event into the AudioGraph.QuantumProcessed handler. You can directly reference the link above for how to do that.

So by default, a frame of data is stored in an array of 480 floats from [-1,+1]. And to get the amplitude, you just average the absolute value of this data.

This part, including handling multiple channels of audio, is explained more thoroughly in my other post.

Have fun!

Upvotes: 1

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