A simple wavetable oscillator in C

I have to program a digital synth for a school graduation project, and while I know most of the theory regarding synthesizers in general, I must开发者_StackOverflow confess to be a programming novice. I have to do it in C, as stated in the title. The simplest way to do it seems to be with wavetable oscillators, also so I can use a ramp wave as a basis for an ADSR envelope. However, I have no idea how to make sure it is in the correct pitch. It is easy to change the relative pitch of the oscillator by changing the increment counter, but how do I determine the absolute pitch of the oscillator?

J.Midtgaard

You need to know the sample rate of the audio stream that you're producing. If your sample rate is fs, and you're trying to produce a tone with a frequency of f, then you need to produce a complete cycle (period) every fs / f samples. Alternatively, during every audio sample, you must advance by f / fs of one cycle. So if your wavetable has n entries to represent a complete cycle, then you need to advance by n * f / fs entries per audio sample.

For example, for fs = 44.1kHz, f = 1kHz, n = 1024, your increment must be 1024 * 1000 / 44100 = 23.22 entries per sample.

Note that you will typically obtain a non-integer increment value. In order to obtain the correct pitch, you should not round this value whilst incrementing. Instead, you should round only when converting your accumulator value to the table index value. (A more complicated approach is some sort of interpolation between entries.)