For a number of years, the FM patent was the most profitable patent that Stanford owned. It's interesting that it was a patent from the music department - not engineering, not biotech that made the most money...
Yamaha DX7 Technical Analysis
111–120 of 130 posts
Re: Yamaha DX7 Technical Analysis
#112Earlier quoted context omitted.
> 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…
I think direct feedback in PM is possible, at least for low modulation indices. The Yamaha implementation is in software, so a one sample delay is the easiest implementation (otherwise you'd have to solve a rather complex equation at every step).
The distinction that I’m making is exactly that. You can’t incorporate direct feedback into a phase modulation synthesizer, you need to incorporate delay into the feedback path. By comparison, you can use direct feedback with subtractive or FM synthesis.
The one-sample delay basically turns the feedback into an iterated function system. With certain parameters, you end up with aperiodic results—cool in theory, but in practice, often just used as a noise source.
Re: Yamaha DX7 Technical Analysis
#113Earlier 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…
That should work fine - the CPU would scan / energize each row independently and then check which columns are connected.
Re: Yamaha DX7 Technical Analysis
#114Yamaha builds so much stuff that this could have been about ... a boat ... a motorcycle ... a guitar ... or the iconic synth :-)
https://www.theonion.com/yamaha-ceo-pleased-with-current-pro...
> Yamaha CEO Pleased With Current Production Of Jet Skis, Alto Saxophones, Snowmobiles, Power Generators, Scooters, Golf Carts
An all time fav
Re: Yamaha DX7 Technical Analysis
#115Also note—there’s no interpolation. Those 4096 entries in the table? That’s all you get. The chip will not interpolate between them.
This was the first thing I scanned the article for. Without interpolation, my understanding is there's likely a TON of aliasing in the raw output, but then that goes through a 16khz lowpass filter that chops everything above 16khz off - cleaning it up.
Re: Yamaha DX7 Technical Analysis
#116I really appreciated both the technical descriptions (esp. those lookup tables) and the historical portions saying where the DX-7 was in relation to other Yamaha FM synths like the 4-operator ones.
I originally got very interested in this when discovering the YM-2151 chip that made 80's arcade game sounds was also found in pro-audio keyboards. They used a very similar YM-2164. This got me to explore the whole DX line including DX-7, DX-9, DX-27S and that keytar that's still popular for bass and talkbox, the DX-100.
Re: Yamaha DX7 Technical Analysis
#117Earlier quoted context omitted.
I think direct feedback in PM is possible, at least for low modulation indices. The Yamaha implementation is in software, so a one sample delay is the easiest implementation (otherwise you'd have to solve a rather complex equation at every step).
The distinction that I’m making is exactly that. You can’t incorporate direct feedback into a phase modulation synthesizer, you need to incorporate delay into the feedback path. By comparison, you can use direct feedback with subtractive or FM synthesis. The one-sample delay basically turns the feedback into an iterated function system. With certain parameters, you end up with aperiodic results—cool in theory, but in…
But if we take the simplest example, f(x) = sin(x + c*f(x)), we can solve it, (numerically). If I run it up to 0.5π for c=0.5, I get something that's (obviously) very close to the function with a short delay. So I take that as the possibility of direct feedback, although in a electronic circuit, feedback also has a minute delay.
Re: Yamaha DX7 Technical Analysis
#118> Each operator has its own phase accumulator. The patent describes a 96 stage shift register to store the phase increment for the 6 operators each of the synth’s 16 voices. Why this was allowed to be patented? This is a pretty much obvious thing to do when you have this kind of limitations. It seems like people reviewing patents don't really understand what they are about. There is plenty of stuff like this in audio…
This specific technique for synthesizing a single operator wasn't patented, its one small part of a much broader patent.
Re: Yamaha DX7 Technical Analysis
#119Earlier 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…
That should work fine - the CPU would scan / energize each row independently and then check which columns are connected.
On a related note (pun intended) I once had a problem with one of these synths and its rubber contact strip. I would hit certain keys then hear a neighbor note or the same note an octave away. I thought there was a short in the scanning circuitry (I had resoldered some joints that appeared weak earlier by a ribbon connector for the keybed.)
Turns out the rubber contact strip was installed inverted. I think this one didn't have notches to make sure it was oriented correctly. After flipping it, notes sounded as expected.
Re: Yamaha DX7 Technical Analysis
#120How is it possible that no one here mentions Korg‘s wundermachine Volca FM, a tiny DX7 compatible, Dexed/KQ Dixie controllable and cheap midi synth with endless possibilities?