how is the sound of the PO's created? (specifically PO-20)

read in an article that the PO20 has a “combination of samples and virtual synthesis”. Been wondering about how the sound in these little things is created and would love it if someone can enlighten me more on this or send me an article where this is explained better. Which sounds are samples, which ones virtually synthesized? Are digital and virtual synthesis the same thing?

I believe there is a small synthesizer circuit because they said “real synthesizer engine” which is probably responsible for making the sounds using DAC (digital audio converter) from its small memory chip. Found this from browsing this forum:

This is such a great way to learn about electronics… having a fun introduction :smiley:

Normally when I hear digital synthesis, I think that the sounds are generated and controlled in some way that the sound remains digital (as in binary information) in some or all of the signal path. This would be like the Meeblip. On the other hand, the OP-1 and microKorg are virtual synthesizers because the entire signal path is a ‘virtual’ circuit that exists with the programming of the microcontroller. There are no physical circuits, just programming.

The POs use DSP chips to virtually synthesize some of the sounds. No telling exactly which ones. But if I had to guess, any of the sounds that are tuned to a scale and can have an envelope defined are synthesized. The drums are probably samples. You can maybe tell by what happens when you go low in pitch. The samples tend to get grainy, whereas the bass or synth parts don’t get grainy, just pitched down.
You can maybe tell by what happens when you go low in pitch. The samples tend to get grainy, whereas the bass or synth parts don't get grainy, just pitched down.

I think thats the best way to determin it.

The PO-20 is definitely 100% synthesized. The sounds it makes are easy (relatively) to synthesize. just square and triangle waves.

The guy who worked with TE designing the new POs’ firmwares made this almost 10 years ago:

sound familiar? similar concept running on the PO-20. just a realtime-editable sequence instead of a preset one.

~5 years ago I had a go myself at synthesis on a relatively underpowered microcontroller
I should revisit that sometime. haven’t worked on it in years.

so some of you say it’s a mix of samples and synthesized sounds, some say it’s all synthesized… any official word/article on this? do they keep it mysterious on purpose?

The POs have so little flash memory (128KB in total, including the code and presets) that samples would need to be extremelly short, given the actual sample rate (48K samples per second, 16bit), even if they are somehow compressed. If I had to implement it, I would use them mostly for drum sounds, or in the attack portion of some synthesized sounds, or as (single cycle) wavetables.

@punji what do you mean "actual sample rate = 48K samples per second x 16 bit" ?
It doesn't sound 16 bits a lot, IMO :)

Couldn't the sounds be produced at very low definition and the output sound produced at higher definition due to intermediate filter ?

The fact that POs are low on memory makes it more likely that sounds are mostly created through synthesis.
From Volca Beats, I'd say that sample based sound would have as basic modulation the speed rate, that would be a hint to detect sample-based from synthesis-based sounds.

As the sounds are produced at very precise intervals, POs "synthesis" might not always need a complete synthesis that would take a pitch as entry, but a sample chain of 16 lo-fi samples. I don't remember the parameters available with the knobs, these could reveal if it's sample-based or synthesis-based, maybe.

@LyingDalai The PO codec is operating at that rate and sample size. The code must generate samples at that rate, but it could be something very simple, like a synthesized square or triangle wave, or a sample at a lower resolution, like 8bit. The volume level and envelop could be applied after that, bringing the result back to the full 16bit dinamic range.

so some of you say it's a mix of samples and synthesized sounds, some say it's all synthesized... any official word/article on this? do they keep it mysterious on purpose?

Have you asked them? It may be something unknown because no one has asked. It seems like consensus is that it is a mix, but that mix would depend on which PO it is. Some may have all samples, others all synthesized, and others a mixture of the two.

which would be sampled? like punji said, 128k isn’t much for room for a wave table.
I doubt it would be both, creating two audio systems wouldn’t be very efficient.