Harmony of Dissonance does sound like it uses more instruments, though, that makes me think of Impossamole, which also seemed to use more instruments somehow. I don't know if whoever did the music on that one somehow overlapped multiple sounds on one channel or what, or maybe it's just my imagination.
There are a few tricks to cram more than one "instrument" on a single channel, for example, you can take two different waveforms, half their heights and add the results together, the resulting waveform would be those two waveforms playing the same note together on the same channel at half the volume, but that of course means that they'll also be tuned the same and have the same pan and volume envelope, so they won't exactly sound like two instruments... But that's not all you can do, if you also half the length of one of the waveforms and repeat it you can have the two waveforms playing at an octave apart! Granted, that also means that it will be playing at half the sample rate, but still...
This is better explained in this image I've made a long time ago:
(H stands for Height and L for Length)And here's an example of me using this trick to put 2 square waves on the same channel and changing the octave of one of them by changing the waveform:
https://orig00.deviantart.net/ad66/f/2017/281/1/7/2_octaves_in_1_channel_by_michirin9801-dbpxmmz.wavThis can be pretty useful if you need two notes an octave apart... It will never sound as good as just putting two instruments an octave apart on two different channels, but since extra channels are at a premium on the PC engine... I think you get the idea...
And no this trick will not do chords, notes can only be offset by an octave, if you want to put a chord on a single channel you'll have to resort to either arpeggios or samples, but I generally dislike arpeggios and samples take up too much CPU time and memory, but speaking of samples, that's another way of playing two instruments on the same channel!
A sample can be basically anything you can fit within the available memory, and Sunsoft's Batman has proved two things on the PCE, that you can loop samples, and that if you use too many samples at once, making an interesting game is barely feasible, (at least at the time and with their code)
So, if you're gonna do sampled percussion for example, you can have not just a sample for each of the drums, hats and cymbals, but also some samples for drums and hats/cymbals playing together, which takes up more memory, but is very much doable! Here's the thing though, the most CPU-friendly frequencies for PCM samples are 7KHz and 16KHz, and hats and cymbals sound rubbish at 7KHz, so most of the games that use sampled drums at 7KHz either don't have hats or do them with white noise, which you can't play together with a sample... I reckon a lot of them do have sampled crashes though... So if you're gonna do them, do them at 16KHz, and pray that the coder doesn't mind having half the CPU time to code the rest of the game >w>';
You could also have sampled chords, but you'd need a different sample not only for the different chord notes, but for the different types of chords, so if you were to do it that way, your compositions would have to be highly pre-meditated...
I'm sure there are more ways to fiddle around with samples, I mean, there's some software-mixing tricks that I'm not gonna get into because I'm not a coder, I'm just an artist, but going back to the wavetable synth now, another trick you can do to fit more than one instrument on the same channel is simply clever timing of the instruments! Basically, you're not gonna play two instruments on the same channel at the same time, but the channel will indeed play two instruments, and alternate between the two at key times, I like to use this trick to do reverb on a single channel, but that only works when I'm playing a lot of notes in quick succession, I can pick the time halfway in between two of the notes to reverberate the note previous to the last one by playing it again at a lower volume and panned differently, like this:
https://orig00.deviantart.net/cbdd/f/2017/281/5/2/1_channel_reverb_by_michirin9801-dbpxtcg.wavI've also used a bit of a more extreme version of this trick in my Hatsune Miku Po Pi Po cover, that song has an instrument that updates at 480Hz as opposed to the usual 60Hz, which is the Kick, but here's the thing, that Kick is playing on the same channel as the Bass!
The way I did is is that for 16 480Hz ticks (2 60Hz ticks) an overdriven sine wave will play and lower its pitch by 4 notes on every 480Hz tick, and on the very next tick after that it switches to the bass if the bass is playing, and switches off the channel if the bass is not playing...
Here's a little sample of it:
https://orig00.deviantart.net/bda9/f/2017/281/9/8/po_pi_po_channel_1_by_michirin9801-dbpxuqu.mp3
