Wavetable | A Rust library for wavetable handling

For context, I'm working in c++ on a stm32f ucontroller doing embedded audio and trying to avoid dynamic allocation.

One of the classes I've written is a wavetable oscillator that is, for the scope of my question, essentially just a bunch of c-style arrays.
I have these files, among others, in a separate folder from the specific project that is using them so I can reuse them across projects with no rewriting or copy/pasting.

The values that fill the arrays are calculated during an initialization routine rather than being hardcoded so that, if I change the "#define tableLength 256" statement at the top that sets the size of the arrays from 256 to some other value, the waveforms will be recalculated properly the next time I compile and flash the program onto the chip.

Since I'm working with limited memory resources, some programs that use this wavetable oscillator may necessitate that these tables be of a smaller size.

Is there a way of specifying the size of these arrays from a given project's main program file so that nothing needs to be changed in the shared wavetable oscillator file?

I'm still pretty early into my programming journey, but my intuition tells me there must be some sort of mechanism to accomplish this since the size of the arrays will still be known at compile time?

I'm trying to avoid changing the array size directly in the shared file, because any file that gets modified since the last flashing gets recompiled during the flashing process.
This means I would have to remember to change the value every time I needed to flash a different product or work on a different project.

For further context, I'm building and uploading the programs using a makefile.
My knowledge of using them is very minimal, so maybe there's a way to specify the size to be used for the arrays from the project's makefile?

Thanks for the help.

I referenced the Pygame MIDI documentation and this code to try to get MIDI input to work. The MIDI Interface (Avid Eleven Rack) receives MIDI data from my MIDI controller just fine in my audio software (Pro Tools). Using Pygame, however, I can not seem to read any information at all.

I've been using math equations to do some basic synthesis for android. The problem with that the formulas keep and keep getting more complicated. So i'm starting to use wavetable synthesis.

So far i can play a single note based on an array of bytes and a predetermined frequency. However when looking for formulas to resample the samples and change the pitch of the wavetable... i just couldn't find a simple solution. There are whole libraries that do this. But it feels like it should be a simple formula to change the sample frequency by downsampling or oversampling.

Is there an easy way of doing that?

Ex: Input is [0,0.5,1,0.5,0...] let's pretend it's a C4

To make it a C3 the expected output should be [0,0.25,0.5,0.75,1,0.75,0.5,0.25,0...]

Basically it's and android's audiopool "rate" property but just the formula that resamples the bytes, which i haven't found anywhere

EDIT:

Thank you to Phil Freihofner for guiding me to the answer. However the original formula he provided didn't smoothed out the end in case of oversampling. But it was a really nice start and i only had to smooth the end. I will attach my end code in case anyone wants a simple function to "Stretch out" a float array.

Trying to do some basic wavetable synthesis (developing an addon for p5.sound) – and wondering if it's possible to dynamically change the waveform of an oscillator while it's playing (constant tone rather than note duration)? In my basic testing, the setPeriodicWave() function has to be called before the oscillator is connected to the AudioContext output then started. Hoping to do some dynamic wavetable synth (with two hard panned channels) for feeding into the X-Y mode of an oscilloscope (for vector visuals based on audio signals). The workflow above, constantly creating a new oscillator with every wavetable change, causes lots of artifacts and phase-shifting issues... it would be great if I could start two oscillators and just update their waveform. Any tips on workflow for doing so? My abstracted workflow:

• create oscillator with 'custom' type (inited with a flat/silent wave)
• custom setWavetable() which uses functions from dsp.js to createPeriodicWave() with array values
• re-init oscillator with this wave (stop oscil, disconnect/trash oscil, init new oscil w/ wave, connect + start oscil)

My program has 30 duplicate symbols errors for the methods length() and table() from the struct below.

This struct can be instantiated in four ways. Each of them is identical but for the table each instantiation refers to and, potentially, the length of that table.

This needs to be known at compile time in order that I can construct an array in the following fashion.

std::array, N> oscillators;.

Could someone please help me to see my error?

I'm currently working on a very basic wavetable synthesizer. I'll try my best to give an understandable overview.

I have a single lookup-waveform with 4096 points, which is sampled by the audio thread. In general, however, a single oscillator has multiple waveforms, which can be morphed by a position parameter. For example, let's take two sine waves where the second one has half the period of the first one. When we play those back at frequency = 440Hz and position = 0.5, we would hear two equally loud tones at 440Hz and 880Hz. Here's a link to the audio (See Sidenote 2).

Due to performance reasons I generate the lookup table on another thread whenever the position parameter changes. And therein lies my problem. Even when I don't change the table position and just periodically generate my lookup table, I get weird, unpredictable glitches. Since the audio data in the table doesn't change in this case, I can only explain this by torn reads. Is that correct? And if so, how do I get around it? Do I use a double-buffer with an atomic pointer-swap after I finish generating the data?

Again, here's the audio for this recording (See Sidenote 2). Also, some oscilloscope data:

Sidenote 1: Populating my lookup table takes ~50,000ns without optimizations and ~10,000ns with optimizations. But the glitches seem to happen with the same probability.

Sidenote 2: The website I uploaded the audio to seems to have introduced some weird harmonics, which are not audible in my video. Just so you know.