audio programming.md

Audio Programming

Digital audio needs to be converted to digital. That means we need to sample from an infinite analog wave to a finite sample rate.

Nyquist Shannon Sampling Theorem

Any band limited continuous-time signal can be accurately converted to and from digital signals when sampled at a rate, at least twice as high as the highest frequency component of the waveform.

• Must go through a low pass filter for band-limiting

• Cycles per second, frequency and Sample per second, and Sample rate both have Hz as a unit.

Dithering

• Dithering is the process of intentionally adding noise to a signal, during the process of quantization, to preserve low-level information and prevent correlated distortion.

References

• Audio Theory

• CppCon 2015: Timur Doumler “C++ in the Audio Industry”

  • Audio is processed in the buffer of relevant size which is just an array of floats.
  • Audio processing should never cause dropout.
  • Don't write any code that is asynchronous, don't know how long will take. No busy waiting. DO lock-free programming.
  • Priority Inversion. Waiting for the low-priority thread.
  • Can't call new and delete. Internally waits for a lock.
  • Don't call RAII objects that use object allocation internally like shared_ptr.
  • No vector::push_back either.
  • Should be done
    • Put your data on the stack.
    • Preallocate your data.
    • Use custom real-time safe containers (lock-free queues, stacks).
    • For larger systems: manage your own preallocated.
    • No io functions, no IPC, no file access.
    • 0(1) is fine, amortised o(1) is not.
      • ordered_set::insert() may rehash.