[Maxd]

dsrb, on 07 August 2013 - 09:16 AM, said:

Maxd, on 06 August 2013 - 04:15 PM, said:

a FM-like subtractive synth waveform channel which can also do low-fidelity WAV file playback

Can you explain what you mean here? Maybe it's technically accurate somehow, but right now, it just looks like a bunch of disparate terms mashed together in a way that makes no sense whatsoever.

Firstly, FM is very different from subtractive, so I'm not sure what equivalence you're trying to paint there. And as far as I knew, the GB's third channel was simply a low-res PCM channel (not WAV, and people need to stop implying the two are equivalent), nothing more, with the fact that it's often used for triangle bass not implying any real subtractive nature.

It is a WAV channel. It plays back uncompressed WAV files, it can also do synthesis that is additive or subtractive, it depends on how you construct your waveforms. You can do many kinds of waveforms (sine, saw, square, with filters such as highpass, lowpass, resonance, bandpass, etc) and cycle through frames of waveforms. You can also modify cutoff, phase, playback speed, looping, and vertical shift of the waveform. This allows for all kinds of colorful sounds similar to FM.

It's definitely not just triangle bass or PCM, you can do some crazy things with the WAV channel.

[GerbilSoft]

Maxd, on 08 August 2013 - 09:12 AM, said:

It is a WAV channel. It plays back uncompressed WAV files
...
It's definitely not just triangle bass or PCM

Here's a hint: Uncompressed WAV *is* PCM. Calling it a "WAV" channel just makes you look like a brainwashed Microsoft lacky who thinks Microsoft invented everything.

The fact that the PCM channel has modulation effects doesn't mean it's "WAV" format. It means it has modulation effects.

[Andlabs]

GB channel 3 plays a loop of 32 4-bit samples (appears to be PCM, but pandocs is unclear) at various frequencies and four volume levels.

[Maxd]

Andlabs, on 08 August 2013 - 09:44 AM, said:

GB channel 3 plays a loop of 32 4-bit samples (appears to be PCM, but pandocs is unclear) at various frequencies and four volume levels.

This is the reference I have been using for homebrew work, it states that channel 3 is wave. It's also referenced in most other ROMs and documentation as wave.

[GerbilSoft]

"Wave" there refers to waveform. It does *not* refer to the Microsoft WAV format.

[TmEE]

Mr. Astley is right here.

[Maxd]

Rereading on what a wav is, I now agree as well with Rick.

Sorry for derailing the thread.

[dsrb]

Maxd, on 08 August 2013 - 09:12 AM, said:

dsrb, on 07 August 2013 - 09:16 AM, said:

Maxd, on 06 August 2013 - 04:15 PM, said:

a FM-like subtractive synth waveform channel which can also do low-fidelity WAV file playback

Can you explain what you mean here? Maybe it's technically accurate somehow, but right now, it just looks like a bunch of disparate terms mashed together in a way that makes no sense whatsoever.

Firstly, FM is very different from subtractive, so I'm not sure what equivalence you're trying to paint there. And as far as I knew, the GB's third channel was simply a low-res PCM channel (not WAV, and people need to stop implying the two are equivalent), nothing more, with the fact that it's often used for triangle bass not implying any real subtractive nature.

It is a WAV channel. It plays back uncompressed WAV files, it can also do synthesis that is additive or subtractive, it depends on how you construct your waveforms. You can do many kinds of waveforms (sine, saw, square, with filters such as highpass, lowpass, resonance, bandpass, etc) and cycle through frames of waveforms. You can also modify cutoff, phase, playback speed, looping, and vertical shift of the waveform. This allows for all kinds of colorful sounds similar to FM.

"similar to FM", ehhh maybe through intentional simulation or coincidence, but it's not at all FM-like by nature. It's just (as myself and, in more depth, GerbilSoft already corrected) a PCM channel.

Similarly, calling it "subtractive" or "additive" is also incorrect since it's simply a PCM channel. People can simulate other types of synthesis using samples, and do it all the time, but that's all it is: simulation. For it actually to be subtractive, it would have to offer its own, separate (read: not built into the sample/s or on the global outputs) filter and whatnot. For it to be additive, it would have to offer multiple sine oscillators to create a composite timbre from scratch. And so on.

I think this illustrates the dangers of only half-knowing what one is talking about.

[Maxd]

dsrb, on 08 August 2013 - 12:31 PM, said:

Maxd, on 08 August 2013 - 09:12 AM, said:

dsrb, on 07 August 2013 - 09:16 AM, said:

Maxd, on 06 August 2013 - 04:15 PM, said:

a FM-like subtractive synth waveform channel which can also do low-fidelity WAV file playback

Can you explain what you mean here? Maybe it's technically accurate somehow, but right now, it just looks like a bunch of disparate terms mashed together in a way that makes no sense whatsoever.

Firstly, FM is very different from subtractive, so I'm not sure what equivalence you're trying to paint there. And as far as I knew, the GB's third channel was simply a low-res PCM channel (not WAV, and people need to stop implying the two are equivalent), nothing more, with the fact that it's often used for triangle bass not implying any real subtractive nature.

It is a WAV channel. It plays back uncompressed WAV files, it can also do synthesis that is additive or subtractive, it depends on how you construct your waveforms. You can do many kinds of waveforms (sine, saw, square, with filters such as highpass, lowpass, resonance, bandpass, etc) and cycle through frames of waveforms. You can also modify cutoff, phase, playback speed, looping, and vertical shift of the waveform. This allows for all kinds of colorful sounds similar to FM.

"similar to FM", ehhh maybe through intentional simulation or coincidence, but it's not at all FM-like by nature. It's just (as myself and, in more depth, GerbilSoft already corrected) a PCM channel.

Similarly, calling it "subtractive" or "additive" is also incorrect since it's simply a PCM channel. People can simulate other types of synthesis using samples, and do it all the time, but that's all it is: simulation. For it actually to be subtractive, it would have to offer its own, separate (read: not built into the sample/s or on the global outputs) filter and whatnot. For it to be additive, it would have to offer multiple sine oscillators to create a composite timbre from scratch. And so on.

I think this illustrates the dangers of only half-knowing what one is talking about.

Perhaps, along with the dangers of going off of old homebrew docs from 1998 that were also incorrect. And the main reason I say it is "additive" or "subtractive" in nature as those are the most common kinds of synthesis you see in games and homebrew. And there are filters for the PCM channel alone, not sure how well it qualifies as being "subtractive" that way. It *can* be additive in nature through manipulation of resonance and high-vibrato (pitch bend) commands that act as oscillators. Combine that with a trick that causes the channel to play to multiple sine waves at once and you have not-quite-real-but-close-enough additive synthesis. But enough of me trying to validate my hacky workarounds, you are correct that at its core it is a low-quality PCM channel, and unless it is pushed to extremes it's basically a triangle wave and sample playing channel.

[TmEE]

Your computer has a timer driven DAC to create a PCM channel as the sole sound hardware. When you listen some kind of music that plays synth stuff or run some music program that does a softsynth it does not make that PCM channel any kind of synthesizer, its still a PCM channel. Well, there's also a filter attached to that channel, to kill all freqs that the sample rate is not supposed to allow to be produced.

[ICEknight]

TmEE, on 12 August 2013 - 08:59 AM, said:

Well, there's also a filter attached to that channel, to kill all freqs that the sample rate is not supposed to allow to be produced.

Just wondering, is that what the GBA hardware does when churning out its usual muffled sound? And in that case, wouldn't it be pretty easy for emulator devs to make their GBA emus to sound like those MIDIs+soundfonts that featured a much higher quality?

Man, what I would give for a GBA emu that allowed for better sample rate and SNES-size expanded view (like some Game Gear emus, even if it won't look too good for many games).

This post has been edited by ICEknight: 12 August 2013 - 10:39 AM

[TmEE]

The GBA hardware most likely has a single fixed cutoff lowpass filter, that is set to safely low level so that PWM carrier freq is not heard (much anyway). If you play 32X games you'll hear a constant whine in some games (like Chaotix). It is the carrier freq and it gets more and more audible as sample rate is lowered. Since sample playback is fully CPU powered on 32X and GBA you cannot go too wild or you'll run out of steam for game...
It becomes a bit hard for emulator to optimize the sound in GBA, because all the emulator knows is the PCM writes... those MIDI+sound fonts and stuff have whole samples to deal with, the actual source data not just the end product. It is hard to make a 22KHz WAV sound good, but if you had all the source data used in that file you can do lot of goodies.

This post has been edited by TmEE: 12 August 2013 - 10:55 AM

[dsrb]

Maxd, on 12 August 2013 - 08:43 AM, said:

Perhaps, along with the dangers of going off of old homebrew docs from 1998 that were also incorrect.

Well, there's a terrible meme going around that the Game Boy has 4 channels of FM, which is just so wrong it's almost painful. So what you thought is, to be fair, quite a bit more reasonable than that. />/>

Quote

But enough of me trying to validate my hacky workarounds, you are correct that at its core it is a low-quality PCM channel, and unless it is pushed to extremes it's basically a triangle wave and sample playing channel.

Yeah, my concern is just that people know what the technology is innately, for the sake of having accurate info, which is important as we both know. Once that's out of the way, it's good that you've explained what you meant and how other types of synthesis can be simulated/approximated.

OT: What was that computer where people used to hack in sample playback by modulating the volume of a really fast square wave? What would that technique be called? Is it technically a form of AM? I'm wondering whether a similar thing might be achievable using sines or other wave shapes. I bet it would sound like ass, though. Actually, the volume would be in logarithmic steps, like the old method of adding squares from the PSG, so that'd make it even less useful. Never mind, I guess... haha.

[Sodaholic]

dsrb, on 12 August 2013 - 11:53 AM, said:

What was that computer where people used to hack in sample playback by modulating the volume of a really fast square wave?

Commodore 64.

dsrb, on 12 August 2013 - 11:53 AM, said:

meme

Huh?

[dsrb]

A meme isn't just a picture with Impact text over it. It's any idea that spreads from mind to mind, regardless of how true it is. The false idea that the GB has 4 channels of FM is far too commonly cited and therefore qualifies as a meme. I guess maybe I should have just said 'common misconception' so that, er, I wouldn't invoke the common misconception about what the word meme means.