VOGONS


First post, by DracoNihil

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Wikipedia states this "feature" was removed in the YMF262 (OPL3), but I don't know what this "feature" even is, what it's sound like, what it's for... I've seen a few, very few DOS games and programs that make use of the RHYTHM but not this "composite sine mode" Wikipedia lists.

Anybody have any idea what this even is?

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Reply 1 of 11, by jwt27

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It was meant to be used for speech synthesis I think. Never tried it myself but I guess setting all operators to use sine waves and additive synthesis would be the same thing.

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Reply 3 of 11, by Lord Nightmare

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It's CSW (composite Sine Wave) synthesis; it also involves the two opl2 timers, and I believe it works almost identically to how it works on other chips like the ym2612 used on the sega genesis. One timer controls pitch, the other controls maybe pulse width?

Edit: CSW speech synthesis for dummies: do LPC analysis of speech. find all the peaks (these are most likely your formants). place a sine wave at each peak starting at the highest one, going down until you run out of sine waves. move around the sine waves each frame (i.e. <=~50ms period) as the peaks change and move.

Edit2: the lowest frequency high peak is most likely your pitch/first formant/'f0'. There are complicated mathematical ways to best estimate the fundamental pitch, or simpler/less accurate ways which are analog (gold) or digital using voting between 5 algorithms (gold-rabiner), and more still. Some simply use the highest peak as the fundamental frequency/pitch.

See wikipedia article on "Sinewave synthesis" for more info.

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Last edited by Lord Nightmare on 2014-08-12, 00:23. Edited 3 times in total.

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Reply 4 of 11, by jwt27

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I don't know how Silpheed did it, but the general idea would be to deconstruct a speech sample into multiple sine waves using discrete Fourier transformation, then you can add these sine waves together to recreate the original sample.

In fact you could create just about any sound, as long as you have enough sine wave oscillators.

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Reply 5 of 11, by DracoNihil

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This is getting interesting. But I don't suppose there are any readily available demos that test this mode? And is it emulated in DosBOX's OPL emulator? I don't have a system in this house that can turn on that can use a legit OPL2 chip. (nor do I think my father even has a old soundblaster with a legit YM3812)

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Reply 7 of 11, by Cloudschatze

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It's pretty easy to see/hear why the CSM mode was excluded from the OPL3, given the pre-processing requirement of the samples, and rather lackluster playback quality. The PWM method, which works equally well on both the OPL2 and OPL3, is arguably the better means of digital-audio playback from the OPL chips.

On the other hand, applying CSM techniques to create a singing Sound Canvas is just flat-out awesomesauce. Here's a thread on the QuestStudios forum with links to videos demonstrating MIDI-based CSM:

http://queststudios.com/smf/index.php?topic=3502.0

Reply 8 of 11, by DracoNihil

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I can't watch any of the links because of a lack of HTML5 player on that website linked in the forum post......

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Reply 9 of 11, by Cloudschatze

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DracoNihil wrote:

I can't watch any of the links because of a lack of HTML5 player on that website linked in the forum post......

Hmm. The "mobile" player applet works with both IE9 and Chrome. You can get around the HTML5 requirement by using the player in the main "NicoVideo" website though (which requires an account).

Reply 10 of 11, by DracoNihil

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The applet that pops up in a popup window needs flash, I don't want to use flash I want to watch with Firefox\Pale Moon's built in HTML5 support. Or VLC if that's possible too.

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