In designing a USB microphone or speaker or whatever... If we upgrade to use a proper microcontroller (whether an 8bit AVR core including a 16bit multiplier, or even our Digital Signal Processor) we can offer further audio processing via USB!
Whether its actually useful is another question...
We can offer to mix different audio "channels" together at different volumes. Adjusting volume is a multiply operation across all the sample of a channel. Mixing involving summing them.
1/?
We can offer, at the peripheral's choice of position in its audio-processing pipeline, to let the host pick between different sound sources. Could be useful for toggling hardware features!
I've already discussed how I'd implement (largely as a side-effect of getting digital audio to work) most of a "Feature Unit" in analogue circuitry. We can use simple formulas (incorporating delayed input) to implement low & high-pass filters, or we can use the Fast Fourier Transform.
2/?
Heck if we do choose to implement using the FFT I'd be tempted to use our hypothetical Digital Signal Processor, after all I specifically designed it for that algorithm!
With that it should be no trouble for software to implement volume, mute, bass/mid/treble tone-control, or delay. Heck we could upgrade to splitting the audio more frequency bands giving us a "graphic equalizer"!
And I neglected to mention Automatic Gain Control earlier for the sole I didn't know what that was.
3/?
If I'm reading Wikipedia correctly ( https://en.wikipedia.org/wiki/Automatic_gain_control ) Automatic Gain Control is a circuit to ensure audio doesn't excede what our speakers can handle. And to smooth results out so its not noticed. Its probably best left to analog circuitry, whilst USB defines a way to request our peripheral enable or disable this circuit.
USB lets peripherals offer to remix the channels they're given into more or fewer channels.
Its probably not worth checking if I can discuss Dolby Prologic.
4/5
I think I'll leave discussing 3D-Stereo, Reverb, Chorus, & Dynamic Range Compression until tomorrow.
And the peripheral can offer to do whatever else it wants, not that it can expect the computer to know what its talking about.
4.3/4.3 Fin for today!
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