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The 1-Bit Forum → Sinclair → next gen engine ideas
The idea above gives this simple PWM modulation type for the 16-bit adders system. It takes two 16-bit accumulators but a single adder:
ld hl,0 ;acc1
ld de,0 ;acc2
ld bc,100 ;adder
loop
add hl,bc
ld a,h
inc de
cp d
sbc a,a
and 16
out (#fe),a
jp loopAnd if we just drop xor N right before cp d, it gives a quite interesting modulation control!
Named the second idea ModPhase, implemented both ideas as experimental sub-engines inside the Ear Shaver EX engine - because it blends pretty well with the design.
Nom nom, that CrossPhase has a very satisfying sound. Great discovery.
I've used the idea behind ModPhase (without the xor modulation) a couple of places, BetaPhase for example. The good thing is that it can be done in the outer loop, which also allows for variable speed (by adding a variable amount to DE). In a pinch, one could even abuse the outer length counter for this, hehe.
Some more cool finds for Phaser4 (currently in development) specifically:
Regular XOR/OR/AND modes in Phaser3 were:
add hl,bc
ld a,h
add ix,sp
xor/and/or ixh
rla
sbc a,a
and 16
out (#fe),aNow, instead of xor ixh:rla we can do more by changing just two bytes - keeping the ix/iy prefix in place:
cp ixh:nop - the CrossPhase
adc a,ixh:add a,h - fat octaving noisy timbre
xor ixh:sub h - more noise in a similar timbre
xor ixh:sub l - very noisy yet still tonal timbre
xor ixl:sub h - periodic noise of one kind
xor ixl:sub l - periodic noise of another kind
And another cool thing is that Phaser3 unrolls the sound loop 4 times for pseudo volume effects. And we're not obliged to use the same 'algorithm' in each iteration, we can mix in any 4, getting even more weird timbres.
Wahoo, now you're on a roll!
Excuse me for having a brain freeze right now, but what is the purpose of the rla in normal phasing mode?
Some tangentially related, inspirational reading: Grayscale on 1-bit LCDs. Would be interesting to try and apply some of the more advanced techniques to 1-bit music. Iirc perevalovds was using error diffusion of sorts for 1-bit sampling.
RLA gets the topmost bit into the Carry after a logic operation XOR/OR/AND that normally does not affect Carry. Honestly, I forgot that I ever invented this method (perhaps borrowed it from you?).
Oh yeah, dithering applied to the 1-bit sound synthesis may bring some quite interesting results! Cool idea, never thought about that.
Ah, yes, of course. I'm clearly getting senile.
Don't think it was me who invented the rla trick. I'd be a cheap bastard and omit both the rla and the sbc a,a. Doing that could potentially open up a few more possibilities here, but with the unrolled loop, modifying 3 bytes might not be worth it. Even without that, I've got a feeling there are more possibilities hiding in those 2 bytes. I just don't see them right now. #dd 0 0 would give a pin pulse, of course, but that's probably not very useful in this setup. You could also swap bc and sp. Then #dd 0, add b/c would give duty control for example, but we already have that via phase offset, of course.
From the article Grayscale on 1-bit LCDs:
"To be honest, I didn’t come to this stage by accident, I have worked with delta-sigma modulators and noise shapers in audio applications before so I know these, and I have been wondering about if they could be applied to driving these LCDs for a long time."
Ha, I missed that gem 
Found a new el-cheapo PRNG/noise generator. It's a bit slower than the usual add hl,de; rlc h variations, but needs only 1 register pair instead of 2. It also sounds a bit different.
ld a,MAGIC_NUM
add a,e
rrca
xor d
ld e,a
inc dFor MAGIC_NUM, most values do pretty much the same, except some that are straight metallic beeps and a few that sound more rumbly.
test.tap plays through all possible values.
The main downside is that we can't smc-hotswap this with regular tone channel code. What could work though is to hotswap it on an 8-bit divider and use a separate 8-bit pre-scale on this. Pre-scale would pitch the noise as well. Unfortunately the perceived pitch of the noise is quite a bit lower than using add hl,de; rlc h. Not sure if it's actually much of an improvement over just lazily reading from ROM:
ld a,(de)
inc deThe 1-Bit Forum → Sinclair → next gen engine ideas
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