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Yamaha DX7 Technical Analysis

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Re: Yamaha DX7 Technical Analysis

#31

Post by 867-5309 »

noizejoy wrote: post #14
tgv wrote: post #4

Plogue, a Canadian software company, have recently released a (software) emulation of the DX-7 in excruciating detail. Here you can see part of the trouble they went through: https://www.youtube.com/watch?v=XJ97iXQrqzw . Suffice to say that they used a logic analyzer to discover gritty details that no other analysis of the DX-7 I know has ever paid attention of.

Another venerable DX7 software emulation worth mentioning is the free and open source Dexed[0], which also doubles as a patch librarian for a real DX7. [0] https://asb2m10.github.io/dexed/

dexed is in the Acknowledgements of the main article

Re: Yamaha DX7 Technical Analysis

#32

Post by lars-b2018 »

Really good article. My first synth, that I had to save up for as a teen, was a DX7. However, wasn't FM synthesis part of the New England Digital's Synclavier system, which was available in the late 70s? Certainly the DX7 was really the first mass-market commercial offering, but I believe the Synclavier was first to market with frequency modulation. I wonder what the arrangement was with John Chowning, if anything, on this.

https://120years.net/wordpress/the-synclavier-ii-new-england...

Re: Yamaha DX7 Technical Analysis

#33

Post by ajxs »

jacobvosmaer wrote: post #22
rcxdude wrote: post #16

Earlier quoted context omitted.

"rate of change of the phase angle" is just a convoluted way of saying 'frequency'

I'm not sure. Intuitively I would think "phase angle" means "offset into the sine wave lookup table". If you step through the lookup table with constant size steps, you would get a sine wave. If the steps are not constant size then you get a distorted sine wave. The "rate of change of the phase angle" would then be the step size.

Author here: This is one reason why I used that term. I was definitely thinking in terms of the 'phase accumulator' looking up the sin table.

Everyone is absolutely right that this is the same as frequency. I think I was used that particular poetic flourish to emphasise how complicated the academic, mathematic explanation is, in contrast with the diagram. Quite likely I picked up that exact phrasing of "phase angle" from some academic literature in particular.

Re: Yamaha DX7 Technical Analysis

#34

Post by joeberon »

ajxs wrote: post #33
jacobvosmaer wrote: post #22

Earlier quoted context omitted.

I'm not sure. Intuitively I would think "phase angle" means "offset into the sine wave lookup table". If you step through the lookup table with constant size steps, you would get a sine wave. If the steps are not constant size then you get a distorted sine wave. The "rate of change of the phase angle" would then be the step size.

Author here: This is one reason why I used that term. I was definitely thinking in terms of the 'phase accumulator' looking up the sin table. Everyone is absolutely right that this is the same as frequency . I think I was used that particular poetic flourish to emphasise how complicated the academic, mathematic explanation is, in contrast with the diagram. Quite likely I picked up that exact phrasing of "phase angle"…

> This is exactly why I used that term

That's a lie, because:

> I think I was used that particular poetic flourish to emphasise how complicated the academic, mathematic explanation is, in contrast with the diagram

is a totally different to what the person you are replying to said

Re: Yamaha DX7 Technical Analysis

#35

Post by ajxs »

mdp2021 wrote: post #20

Waiting now for the SY99 ;)

Author here: I wish! I own a TG77, and it's an absolutely amazing synth. While I don't have any direct experience with the SY99, the 77 was so far ahead of its time. The sheer amount of features packed into the synth alone is an engineering feat.

Re: Yamaha DX7 Technical Analysis

#36

Post by HelloNurse »

jacobvosmaer wrote: post #22
rcxdude wrote: post #16

Earlier quoted context omitted.

"rate of change of the phase angle" is just a convoluted way of saying 'frequency'

I'm not sure. Intuitively I would think "phase angle" means "offset into the sine wave lookup table". If you step through the lookup table with constant size steps, you would get a sine wave. If the steps are not constant size then you get a distorted sine wave. The "rate of change of the phase angle" would then be the step size.

What matters for FM is an instantaneous quantity: the derivative or increment of the instantaneous phase, i.e. how the phase changes from sample to sample.

What is usually called frequency, and has the same value in boring cases like an unvarying sinusoid, is the inverse of the period of the resulting sound as someone would hear it, which is not instantaneous and needs on the order of one period's worth of samples (usually more) to estimate, for a certain definition of period (e.g. interval between zero crossings) or a certain mathematically reasonable calculation (e.g. estimating the frequency of the strongest component from a fixed-length window of past samples).

Re: Yamaha DX7 Technical Analysis

#37

Post by ajxs »

joeberon wrote: post #34
ajxs wrote: post #33

Earlier quoted context omitted.

Author here: This is one reason why I used that term. I was definitely thinking in terms of the 'phase accumulator' looking up the sin table. Everyone is absolutely right that this is the same as frequency . I think I was used that particular poetic flourish to emphasise how complicated the academic, mathematic explanation is, in contrast with the diagram. Quite likely I picked up that exact phrasing of "phase angle"…

> This is exactly why I used that term That's a lie, because: > I think I was used that particular poetic flourish to emphasise how complicated the academic, mathematic explanation is, in contrast with the diagram is a totally different to what the person you are replying to said

I've edited my post to clarify. It's a reason why I used that term. The second part of my post is not directly addressing what GP said. One of my aims in writing this article was to create something that could be interesting to read, with someone like myself as the target audience. Part of that involves using some artistic flourish.

Re: Yamaha DX7 Technical Analysis

#39

Post by TonyTrapp »

lars-b2018 wrote: post #32

Really good article. My first synth, that I had to save up for as a teen, was a DX7. However, wasn't FM synthesis part of the New England Digital's Synclavier system, which was available in the late 70s? Certainly the DX7 was really the first mass-market commercial offering, but I believe the Synclavier was first to market with frequency modulation. I wonder what the arrangement was with John Chowning, if anything, o…

I think this explains the timeline quite well: https://priceonomics.com/the-father-of-the-digital-synthesiz...

> Somewhere in this lull, a tiny Vermont-based synthesizer company aptly named the New England Digital Corporation beat Yamaha to the punch by producing the world’s first digital synthesizer, the “Synclavier.” Though only 20 units were sold at $41,685 each, and they were all reserved for top-notch musicians, Stanford took no chances, and swiftly sued the company for infringing on its FM synthesis patent. From that point forward, the university received a sum of $43 every time a Synclavier was sold.

Yamaha had been working on FM synthesis for a few years already at that point.

Re: Yamaha DX7 Technical Analysis

#40

Post by varispeed »

> 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 space.

E.g. this one https://patents.google.com/patent/US20170060527A1/en

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