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Yamaha DX7 Technical Analysis

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Re: Yamaha DX7 Technical Analysis

#101

Post by TheOtherHobbes »

S_A_P wrote: post #80
z5h wrote: post #71

Earlier quoted context omitted.

I like to think I’m a synth nerd in the know, and certainly chat a lot and read synth forums. But Plogue have flown under my radar. This looks like great stuff at a good price. Do you own any of their soft synths?

Plogue has been around for a while but nobody could fault you for missing them. I have been and active member of KVR VST for over 20 years which is where I heard of them but never owned anything of theirs. It was only recently announced that they released this 'sample accurate' DX7 clone. I have TX7 for and the Arturia DX-7V. Typically FM or Phase Distortion(Casio CZ synths) arent really the type of sound I go for, b…

Bidule has been around for ages - at least 10 and maybe even 20 years.

Re: Yamaha DX7 Technical Analysis

#102

Post by TheOtherHobbes »

jacquesm wrote: post #99
QuadrupleA wrote: post #98

Earlier quoted context omitted.

You can definitely do 2 simultaneous keys unambiguously without diodes; 3 keys is where you sometimes get "phantom keys" by bridging other rows / columns to each other. Depends on the matrix layout though, if you have say an 8 x 8 matrix for 64 keys and each pressed key is on the same column or row, you can read 8 simultaneously without any problems. Most PC keyboards leverage this so they can skip diodes, and just r…

Hm. I don't know about that, I thought that the problem already existed for 2 diagonally opposing sets of buttons: you can't tell the difference between the two. so: | | | | | | ---+-+-+-+-+-+----- | | | | | | ---+-+-*-+-+-+----- | | | | | | ---+-+-+-*-+-+----- | | | | | | and | | | | | | ---+-+-+-+-+-+----- | | | | | | ---+-+-+-*-+-+----- | | | | | | ---+-+-*-+-+-+----- | | | | | | Would look identical to the CPU wi…

https://patents.google.com/patent/US5430443

Re: Yamaha DX7 Technical Analysis

#103

Post by weatherlight »

weatherlight wrote: post #61

I was under the impression that, despite the name, the Yamaha FM synths didn't actually use frequency Modulation but rather phase modulation. With Frequency modulation you can't have an operator feed back on its self. If you take a DX7 patch and implement it on something like the PreenFM2 or PreenFM3 (which uses actual FM), any algorithm with more than a few operators is going to sound quite different. I still love t…

also on spotify -> https://open.spotify.com/track/0m3XklXAjsJAnSMgl2Upif?si=391...

Re: Yamaha DX7 Technical Analysis

#104

Post by TheOtherHobbes »

There's a history of Chowning and FM here. Practical FM is closely linked to CCRMA's Samson Box which was designed by Peter Samson of System Concepts, who were better known for building affordable(ish) DEC KL10 clones.

https://120years.net/tag/ccrma/

When Chowning met Dave Bristow, who was Yamaha's product specialist and designed many of the DX7 presets, he apparently asked if Bristow could explain FM to him because he didn't really understand how to use it.

This was partly a joke and... partly not. It was also before they wrote this together:

http://www.burnkit2600.com/manuals/fm_theory_and_application...

Re: Yamaha DX7 Technical Analysis

#105

Post by HeyLaughingBoy »

mikewarot wrote: post #100
HeyLaughingBoy wrote: post #91

Earlier quoted context omitted.

I have to ask. Was the MCU by chance an MC68HC705K1? Asking for a friend :-)

It was a 68HC11, I forget the specific model number, they had a few development boards for $68.11 in the local college bookstore, so that's how I prototyped it. ;-)

I asked because in interviews I used to mention the amount of functionality I stuffed into a 'K1, which ISTR had 511 bytes of program memory.

I recall that HC11 version too! I bought the PLCC version and made my own dev board with a through hole PLCC socket :-)

[edit] memory just caught up to me. The HC05K1 had 504 bytes of program memory, not 511.

Re: Yamaha DX7 Technical Analysis

#106

Post by jacquesm »

TheOtherHobbes wrote: post #102
jacquesm wrote: post #99

Earlier quoted context omitted.

Hm. I don't know about that, I thought that the problem already existed for 2 diagonally opposing sets of buttons: you can't tell the difference between the two. so: | | | | | | ---+-+-+-+-+-+----- | | | | | | ---+-+-*-+-+-+----- | | | | | | ---+-+-+-*-+-+----- | | | | | | and | | | | | | ---+-+-+-+-+-+----- | | | | | | ---+-+-+-*-+-+----- | | | | | | ---+-+-*-+-+-+----- | | | | | | Would look identical to the CPU wi…

https://patents.google.com/patent/US5430443

Ah I see, clever!

So in essence because the diode solution requires rows times columns diodes and this one only has a couple of parts per row and per column it scales better and for larger keyboards will end up with a substantially reduced parts count and a simpler circuit.

That patent is quite a bit younger than the synth though, so it's kind of logical that that technique would not be used, and my hunch on why they used those diodes back then is likely correct, even if we have a smarter way of doing this now.

Re: Yamaha DX7 Technical Analysis

#108

Post by nyanpasu64 »

weatherlight wrote: post #62
jacquesm wrote: post #47

Earlier quoted context omitted.

Why?

The DAC conversion is hard to nail in combined with the 12-bit certain crunchiness to the old Yamaha FM synths.

Retro synth emulators are terrible at proper analog audio emulation. Higan (the "most accurate" SNES emulator) uses cubic teaming for the output without an attempt to emulate the stairstepped ZOH DAC or analog lowpass, or implement a brick wall. Plogue is one of the few developers to produce proper analog emulation, and they say they document all their research (https://youtu.be/V3yWXVAZgO0), but I'll have to check again to see if I can find it in the video or not.

Re: Yamaha DX7 Technical Analysis

#109

Post by inetsee »

If anyone is interested in exploring software based FM synthesis, Csound is capable of doing FM synthesis [1], and can model the Yamaha TX81Z FM Synthesizer [2]. (I had one years ago and I loved the sounds).

[1] https://csound.com/docs/manual/SiggenFmsynth.html

[2] https://csound.com/icsc2019/proceedings/3.pdf

Re: Yamaha DX7 Technical Analysis

#110

Post by nyanpasu64 »

klodolph wrote: post #63
weatherlight wrote: post #61

I was under the impression that, despite the name, the Yamaha FM synths didn't actually use frequency Modulation but rather phase modulation. With Frequency modulation you can't have an operator feed back on its self. If you take a DX7 patch and implement it on something like the PreenFM2 or PreenFM3 (which uses actual FM), any algorithm with more than a few operators is going to sound quite different. I still love t…

> I was under the impression that, despite the name, the Yamaha FM synths didn't actually use frequency Modulation but rather phase modulation. With Frequency modulation you can't have an operator feed back on its self. It’s true that it’s phase modulation, but phase is just the derivative of frequency, and the derivative is a linear operator (essentially a 6dB/oct EQ). So I don’t think it’s an especially important p…

> phase is just the derivative of frequency, and the derivative is a linear operator (essentially a 6dB/oct EQ).

FM (if strong enough to create negative frequencies) and PM are equivalent when you're modulating a signal with a sine wave. As soon as you chain modulators, they're no longer mathematically equivalent or capable of producing the same sounds, since frequency-modulating a signal by a complex wave is different from phase-modulating a signal by the same complex wave (which can produce sharp corners given a bounded input with sharp corners).

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