SCC synthesizer...

Page 6/7
1 | 2 | 3 | 4 | 5 | | 7

By msd

Paragon (1372)

msd's picture

09-04-2018, 10:10

Quote:

The Amiga sound chip is a PCM player (just like the OPL4) rather than a wavetable synth.

. The opl4 is considered a wave table synthesizer. The SCC also uses a form of PCM. Both the opl4 and the scc have a limited size for a wave form, 32 Samples for SCC and 65536 Samples for the opl4. Also the opl4 has an lfo and envelopes in hw. iirc the amiga doesn't have this. That is a 'pure' sample player. Besides they both use PCM, the opl4 is nothing like the amiga.

By Grauw

Ascended (8384)

Grauw's picture

09-04-2018, 13:24

The OPL4 calls itself wave table synthesizer, but if you look up the common definition of wavetable synthesis then that does not describe the OPL4, rather it is a fairly standard sampler / rompler.

Technically speaking yes the OPL4 has a sample size limitation as well, but what defines wavetable is that it’s a (short) periodic waveform, and even if you would play the 65536 samples at 44.1 kHz the period is over a second which is way below the audible spectrum to be perceived as a distinct tone. Also the presence of hardware ADSRs etc doesn’t make it any less of a rompler, just a more feature rich / more hardware accelerated one. Like an FM synthesizer is FM with or without those features as well.

Conceptually, a sampler is about playing back prerecorded samples, often with loop points etc. Personally I don’t really consider this synthesis, though I guess it does fall under that definition.

Then there’s four forms of synthesis (sound building): Subtractive synthesis is about taking base waveforms and applying filters. FM synthesis is about audio-rate modulation of waveform frequencies. Additive synthesis is about building sounds by adding overtones, organs are an example of this. And wavetable synthesis is about defining the waveforms manually. There are more types of synthesis like granular synthesis which are fairly popular lately, but I would say these are the main four.

Wavetable synthesis can partially emulate subtractive and FM synthesis as well with the right tables, and is actually near identical to additive synthesis. 4-op FM synthesis can also do limited additive synthesis by using the all-carrier algorithm and increasing multipliers for each operator.

Back to the SCC, actually to do proper wavetable synthesis you also want to back it with a table of waves which you can scan through with an ADSR or other forms of modulation.

By Grauw

Ascended (8384)

Grauw's picture

09-04-2018, 12:08

Sorry to type so much hehe, procrastinating at work (I mean, compiling), and I have opinions(tm) :D.

By wolf_

Ambassador_ (9767)

wolf_'s picture

09-04-2018, 13:10

Whoever invented the term AM-mode? Is it in any official documents by Yamaha? If 'AM' is to be called 'amplitude modulation', then obviously this is the wrong term. There's no such thing as amplitude modulation in FM, only frequenty modulation. Even if one operator has active feedback on itself, then still the effect is FM, not AM.

By Grauw

Ascended (8384)

Grauw's picture

09-04-2018, 13:24

Sorry, you’re right that’s wrong hehe Smile, typed without thinking. I think for some reason MoonBlaster used it, and I had the PSG AM on my mind while I was typing it, so those thoughts combined into "AM mode" -_-;;. I meant with the all-carrier algorithm. Edited.

By yzi

Champion (441)

yzi's picture

09-04-2018, 18:38

Amiga is more versatile in creative sound mangling, because it allows changing the waveform memory with the CPU on the fly, without interrupting playback. OPL4's stronger sides are the higher number of simultaneous channels, higher bit depth, higher sampling rate, hardware envelopes and FM of course.

It's hopeless to try and get people, especially middle-aged MSX hobbyists, to understand or care about what wavetable synthesis "really" meant. I think on Amiga you could do "real" wavetable stuff, but not on OPL4.

By syn

Paragon (1920)

syn's picture

09-04-2018, 21:58

Also afaik opl4 offers no sample offset tricks which are very nice to use in pc trackers (fake filter effects for example or freaky cut-up drum loops)

By yzi

Champion (441)

yzi's picture

09-04-2018, 23:33

In SootSound, I implemented a limited sample offset 9xx ProTracker command by creating a separate sample info entry for each sample+offset combination, but the total number of samples is limited to a maximum of 128, which limits how many offsets can be used until the converter says no can do. However, that's not the only annoying restriction in OPL4. The volume of a sound channel cannot be completely muted without stopping the sample playback, so you can't do things like C40, C00, C40, C00... And of course, the sample parameters cannot be changed without completely switching off sound generation for the whole thing. Designed by a committee, to a specification, not for creative hacking around?! Wink Why would anyone want to modify the instruments while playing???

By syn

Paragon (1920)

syn's picture

09-04-2018, 23:46

Yes 128 is not enough if you want to do it on a few different samples as well. But hey, isn't msx music making a fight/struggle with (or being creative within the) restrictions? Imho thats part of the beauty of msx music making. If i don't want restrictions i fire up a DAW on pc Smile

By msd

Paragon (1372)

msd's picture

11-04-2018, 13:54

@ Grauw : The definition is vague. You can use the opl4 in the same method as the SCC. Tongue Anyway. Never mind.

Page 6/7
1 | 2 | 3 | 4 | 5 | | 7