new accurate DX7 emulation being developed

[tristan-]

I was browsing the YamahaDX community on Yahoo and stumbled upon this message, so I'm only the carrier. thought I should be posting that here as well.

I'm working on an open source synthesizer (mostly for Android, but I'm developing on Mac so it runs on that too) that contains an accurate DX7 emulator. To this end, I've been doing a lot of reverse engineering, mostly by poking MIDI into the keyboard (I actually have a DX7s) and measuring the audio output (at 192kHz, 24 bits).

I'm figuring out lots of details, some of which I'm posting on the wiki (I hope to do more writeup, but it takes time and generally with the time I have I enjoy actually coding and playing).

http://code.google.com/p/music-synthesizer-for-android/

Right now, I've identified a lot of sources of noise, artifacts and cruft. For the most part, in my implementation I'm cleaning it up, but I'm seriously considering a "dirty" mode that attempts as close to bit-identical as possible. The artifacts include:

1. Minor aliasing due to limited bit depth of the sine luts (I haven't confirmed the actual bit depth yet as that's hard to measure directly, but guess it's around 12, certainly at least 10).

2. Envelope is quantized to 6/256 dB steps, and has some clock stepping. I think this makes attacks a bit "chiffy", which might actually help woodwind sounds, but so far my emulation smooths it out (linear interpolation of gain, updated every 64 samples).

3. LFO and modulation is quantized the same, and only updates about every 3ms so there are steps. It's smoothed out a bit, but not enough to make it inaudible.

4. DAC distortion. I think this makes the sound warmer, as it's pretty different than a pure sine, which sounds really thin.

5. Noise. Boy is the DX7 noisy (even the s). I'm guessing most people _won't_ want this, as it's hard to really get rid of, and easy enough to add if you really want it.

6. Ordinary FM aliasing I'm keeping, because the only sure way to get rid of it is to run at a higher clock (DX7 is 49096Hz, which is close enough to 48KHz I'm just going with the latter).

How much do people prefer preserving the original dirt, vs cleaning it up?

One thing I'm looking for is patches I can distribute under an open source license. If you're willing to contribute, let me know. If you've got a bunch of _high quality_ patches and want some compensation to relicense them as open source, let's talk.

And I'm interested in connecting with other people who might want to collaborate on this in one way or another. My primary interest is the sound engine, which itself I'm writing to be portable, so it could be adapted to other platforms besides Android.

Taken from: http://launch.groups.yahoo.com/group/Ya ... sage/14482

[penguinfromdeep]

That's really cool! I really hope he adds 'dirty' mode and noise too! I want authenticity above all!!!

[bpblog]

seems very interesting, although i won't be able to use it if it ends up being Android/Mac only.

[Teksonik]

I've got an Android device but how would I play the synth with my keyboard controller ? I can get audio out but.....

FM8/FM Heaven are good enough emulations for me. I used to own a DX7 and TX7 but other than a handful of sounds like Tubular bells the old DX sounds have become rather tired and dated in my opinion. I'm more interested in new sounds that FM8 can make than dead accurate emulations of the DX....but having said that I might buy the Android version just for the heck of it.....

[EvilDragon]

Android, OSX, how about Windows?

[Teksonik]

Android, OSX, how about Windows?

Yea how about programming it for use on real computers......

[Spitfire31]

…how about programming it for use on real computers......

Ah - you mean Linux machines!

That aside, I must confess that I can't quite see the payoff in spending a huge amount of time and energy, recreating in clinical detail - warts and all - the sound of this 30 year old (launched in 1983 and I got my DX7 at Xmas that year).

While it was sensational at the time and became iconic, after a few years in my home studio it was relegated to serve as mother keyboard with an E! add-on.

While it performed admirably in this role until quite recently (it's built like a tank!), I always found its sound somehow lacking depth and lustre and I much prefer the spin offs, such as FM7 and FM8.

So, I won't be standing in line for the emulation.

FWIW.

/Joachim

[layzer]

meh, no windows... no biggie. make a software SY77 that
is true to the hardware only for mac and android and i might be a tad disappointed.

[Spitfire31]

…make a software SY77 that is true to the hardware…

Now we're talking!

/Joachim

[earlevel]

Agree, the DX7 was very noisy—hated that—tolerated it and used it a lot, but hated it. I remember griping about it, and people would say that it didn't seem noisy to them (because they didn't hear hiss when they weren't playing it)...no, I mean the sine waves...

[Acid Mitch]

How much do people prefer preserving the original dirt, vs cleaning it up?

If you don't preserve the dirt and clean it up your claim of "accurate DX7 emulation " is untrue, or questionable at the very least..
I don't think you should change anything about the sound.

[Sendy]

Mmmmmm, cruft!

[mx25]

Hi.
i dont see info on value of "key scaling" in your wiki.

[Nightpolymath]

Not a big fan of the DX7 but good luck in your endeavors nonetheless.

[Teksonik]

after a few years in my home studio it was relegated to serve as mother keyboard with an E! add-on.

While it performed admirably in this role until quite recently (it's built like a tank!),

Did the E! board allow the original DX7's to transmit the full velocity range ? (the early versions were limited to a max of 100 if I remember correctly). Whenever I played my DX from my ESQ-1 the patches would overdrive like crazy because of the velocity difference....I suppose a true emulation would incorporate that "feature" as well......