Genesis - SNES audio comparison

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sheath
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Genesis - SNES audio comparison

Post by sheath » Sat Dec 20, 2008 4:14 pm

Hello all,

I figured this would be the place to go for some decent technical discussion. I'm trying to do a fact based technical comparison of the Genesis' sound capabilities compared to the SNES and TG16 in particular. I think it should be obvious that cost factors prevented the Megadrive hardware from having an ADPCM based sound chip, but that isn't the point I want to explore. I need a method to scientifically break down the actual audio output from game consoles so that a factual analysis can be performed.

It seems to me that if two consoles were outputting sound at similar frequencies then neither was intrinsically superior. My ears tell me that this is the case with this generation of console, but I'd like some hard documentation to prove it. I will then post a new feature on gamepilgrimage.com with the breakdown. Any and all help will be appreciated.

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Post by Shiru » Sat Dec 20, 2008 4:37 pm

All three consoles uses different methods of sound synthesis. So they can't be compared directly, their sound systems are not better or worse than another, it just different.

Well, if you want to compare digital (sampled) sound capabilites, SNES is far superior than SMD and TG16, there is not much to discuss (pure hardware sampler vs. synth plus software-controlled low-quality DAC).

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Post by sheath » Sat Dec 20, 2008 5:14 pm

Do we have any comparison of what frequency each system output at? I know that they all convert the audio to analog to be sent to the A/V outs. Having recorded from all three systems I have found that I had to run a custom noise filter in Cool Edit Pro to get them to sound like the actual output again. From listening to the music from all three systems I think the comparison is as you say, different but not better. Having some sort of specifications on what audio quality actually output from the systems would help prove this.

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Post by Huge » Sat Dec 20, 2008 11:35 pm

>Do we have any comparison of what frequency each system output at?
SNES outputs at 32khz, Megadrive uses an FM chip so it's not really possible to give an exact samplerate.

The only thing you can compare the snes and megadrive is sound sampling capabilities. The Megadrive only has one channel and rather low samplerate for that. SNES has 8 channels and a high samplerate (ruined by low amount of ram to work with, though).

But beyond that the Megadrive has a good FM engine. You can do wonders with FM, I honestly don't think the YM2612 was ever pushed to it's limit (probably because the lack of documentation).

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Post by Shiru » Sat Dec 20, 2008 11:50 pm

Huge wrote:>Do we have any comparison of what frequency each system output at?
SNES outputs at 32khz, Megadrive uses an FM chip so it's not really possible to give an exact samplerate.
..
The Megadrive only has one channel and rather low samplerate for that. SNES has 8 channels and a high samplerate (ruined by low amount of ram to work with, though).
Why not possible? We know YM2612 serial DAC samplerate and we know how fast we can send sample data to DAC (forgot exact values, you can find them on this forum). It actually possible to use higher sample rate than 32kHz. Problem is that this DAC is 8 bit and all timings are software-controlled. Other part of problem is than Z80 (which often used to play samples) has very slow bankswitch system, it can use only 32K of ROM at once.

Many SMD games had low quality sampled sounds because Z80 also controls FM synth (and still must send data to DAC with precise enough timings, though there is no even interrupts from HW timers). Other part of problem is that higher samplerate means larger samples (want 32kHz? 32K for one second of sound then), and Z80 have no time to implement compression with good samplerate. So, quality digital samples (though not comparable with SNES anyway) is question of cartridge ROM size (i.e. price) and complexity of sound driver (must be state-of-art code).

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Post by Huge » Sun Dec 21, 2008 1:44 am

Shiru wrote:Why not possible?
Because I meant comparing the FM part in the ym2612, not the dac, for the samplerate question. I don't think it's possibly to measure a "samplerate" for frequency modulation.

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Re: Genesis - SNES audio comparison

Post by tomaitheous » Sun Dec 21, 2008 3:07 am

sheath wrote:Hello all,

I figured this would be the place to go for some decent technical discussion. I'm trying to do a fact based technical comparison of the Genesis' sound capabilities compared to the SNES and TG16 in particular. I think it should be obvious that cost factors prevented the Megadrive hardware from having an ADPCM based sound chip, but that isn't the point I want to explore. I need a method to scientifically break down the actual audio output from game consoles so that a factual analysis can be performed.

It seems to me that if two consoles were outputting sound at similar frequencies then neither was intrinsically superior. My ears tell me that this is the case with this generation of console, but I'd like some hard documentation to prove it. I will then post a new feature on gamepilgrimage.com with the breakdown. Any and all help will be appreciated.
I'm not sure what you looking for is sample rate. All three audio hardware generate high enough 'sample rate' for output, but it doesn't really give you any idea what kind of instrument sounds you can make.

Like Shiru said, you can't really compare the audio units directly. If anything though, I'd say the SNES has less limitations for creating 'different' instrument sounds out of the three. The 2612 tends to have an signature FM sound to it - like almost all FM chips from that era. Great if you want that sound, not so great if you want something sounding much different. PCE tends to sound very sharpish since most waveforms used by developers tend to be square/triangle/saw/etc and sine for bass. PCE can generate up to a 3.57mhz frequency, but the period system usually keeps it in the 2khz-44khz range. PCE and MD has the disadvantage compared to the SNES in creating realistic instrument sounds. But personally, I don't think it's really a big disadvantage. Plenty great tracks without realistic sounding instruments ;)

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Post by HardWareMan » Sun Dec 21, 2008 4:53 am

As I already said:
I will try to explain some HW "features" of YM2612. As I told, I done some research work with analog part of YM2612 on one russian forum (wich is already dead). You can do this to, using a good oscillograph. YM2612 using time-multiplexed channel mixing. It use 6 "slots" on every cycle. It looks like this:
...(1)-(2)-(3)-(4)-(5)-(6)-(1)-(2)-(3)-(4)-(5)-(6)-(1)-(2)...
Every "(n)" (where n - number of channel) is an analog equivalent of amplitude of single channel. And "-" is gaps, wich 1/2 of Ucc of analog part. And cycle frequency is about of 20kHz. Then goes active Low Frequency filter (on operation amplifier), wich cut off all below about 18-20kHz. But big difference of amplitude between gaps and maximum channel amplitude create strong harmonic frequences, wich depend from amplitude and frequency of every channel. Now, you can imagine, what happens when you using all 6 channels with FM... By the way, becouse only 6 "slots" in output DAC of YM2612, internal "DAC" can be only replace one of FM channel number 6. "DAC" - becouse it is simple register, sets output DAC of YM2612.

I believe that engineers has an strong reason when projected YM2612 to do this terrible analog part (against of 6 separate DACs). Sorry, but now I can not put photos waveforms from oscillograph.

So, using 18kHz samplerate you get big aliasing.
BTW Becouse every channel has that small cycle duty high frequences sounds much better, then in emulators.
Image
So, in the YM2612 case we can calculate it's output samplerate. Here I'd done some calculations, based on oscilloscope measurement.
Yes. It's exactly 0.005ms per division. But your math is wrong. We see all 6 channels on screen, so whole screen is exactly shows samplerate. But it has 10 divisions, not 6. So time is 0.005x10=0.05ms or 20kHz, what I told you. And I very interesting with "ladder" defect on signal... It's not amplifier nor filter fault - I was checked it very carefully.

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Post by TmEE co.(TM) » Mon Dec 22, 2008 12:29 am

I have no PCE/TG16 to mess with, but I have some SNES and MDs.

MDs all have poor analog parts, especially MD2, which has very heavy filtering plus distortions. Early MD1s have relatively good sound outputs though its still not very crisp. SNES with separate SPC have better analog part than SNES with onboard SPC. My European SNES with onboard SPC sounds as poor as a MD2 while the SNES with separate SPC sound like my early MD1.
Real YM2612 chip is less accurate than the implementation in the ASIC in MD2s, I prefer the ASIC version as it has less aliasing noise. With a sound mod done to a MD2, it will sound better than anything else. My MD2 : http://www.hot.ee/tmeeco/MYSMD2.JPG

SNES music sounds good as long as good samples are used, but the 64K of RAM for sound (and according to Steve Snake, official docs said ony 32K is available, and many games stick to it) is very little, and it shows (well, sounds :P) in many games. Real SNES sounds nothing like emulators do, I hope SNES will sound as good after I've done an audio mod to it... I don't really hope for anything though, you can't really make 8KHz or less sample sound crisp and clean.
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Post by Huge » Mon Dec 22, 2008 12:44 am

TmEE co.(TM) wrote:Real SNES sounds nothing like emulators do
Why? iirc the spc700 has been cracked by now and is perfectly emulated with the exact same filtering as on the original console.

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Post by TmEE co.(TM) » Mon Dec 22, 2008 1:01 am

I meant without filters and other crap that make things sound bad... filtering out the part of the sound that tickles your ear means automatic poorness to me... that's the reason I'll do some work on a systems sound part, to get rid of any filtering that happens in order to get the sound crisp. So far, Saturn, Dreamcast and Mega CD don't need any mods to sound good.
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Post by Huge » Mon Dec 22, 2008 3:07 am

You mean the analog filtering? imo it just adds to the characteristics of old machines. See the Commodore 64.

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Post by TmEE co.(TM) » Mon Dec 22, 2008 9:46 pm

I'm having relatively big HiFi at home, and my whole life I've listened stuff that's crisp and clean, and if a game console is not like so, I'll do my best to get it so.
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Post by AamirM » Tue Dec 23, 2008 11:51 am

Huge wrote:
TmEE co.(TM) wrote:Real SNES sounds nothing like emulators do
Why? iirc the spc700 has been cracked by now and is perfectly emulated with the exact same filtering as on the original console.
Err...If my memory serves me correctly, SPC700 does not produce the sound (its a CPU, analogous to Z80 in MD). Its DSP (S-DSP) which produces the actual sound. But yeah, IIRC, blargg cracked it completly sometime ago.

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Post by Huge » Tue Dec 23, 2008 1:14 pm

Yeah, I meant the whole audio subsystem that handles it. But I'm sure the SPC timing itself had many bugs and "unknowns" for a long while, that was only fixed recently. Then again the last time I looked into SNES emulation was many years ago, I just recall SPC timings never being right (messing up Earthworm Jim out of all games - either the normal game or a prototype rom of it).

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