Hello. I’m Kyle and I’m creating some open-source music-making hardware. A samplery synthy sort of thingamajig… a synthamajig. I’m starting this dev log to share the process. If you’re interested in audio synthesis, DSP, embedded software or hardware design, you can follow along using the RSS feed.
sample storage
I’ve been thinking about sample storage and what the path is from disk to the headphone jack. The RP2350 supports two 16 MB external memories on the QSPI interface. One of those will be the program flash, so the other can be a 16 MB RAM. That’s in addition to the 520 KB of SRAM on the chip. By far the simplest thing to do would be to load samples used in a track into the 16 MB RAM from the sample library on the non-volatile disk (which is currently an SD card, but will hopefully be soldered-down NAND flash)....
sample rate conversion
I’ve been looking at sample playback. The main issue here is changing the pitch of the sample without introducing (too many) artifacts. When we pitch a sample up, any frequencies that go over the Nyquist frequency will fold back and we will have aliasing. When we pitch a sample down, we also pitch down the image of the sample centred at the sample rate Fs, and some of it will enter the audible range....