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PWM sound on a DX7
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Jordan15
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#1
21st February 2011
Old 21st February 2011
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PWM sound on a DX7

I havent got a DX7 yet, but looking through the manual at the parameters I noticed some odd things, like no filters, and no PW or anything like that.

I've done some looking around for things that would help me correlate FM with subtractive to make things more easy to understand, and the only thing I could come across was that adding feedback makes the sine more saw-like which was useful to me.

Does anyone know how to:

1. Make the sine into more of a square wave, and

2. What you'd have to do with the modulator to give the original carrier sine wave a PWM sound. My best guess would be some kind of LFO with the modulator, but I don't know if LFO can be applied to single operators or not.


Thanks guys
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21st February 2011
Old 21st February 2011
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i'd start by reading up on FM synthesis

i think the yamaha FM synths actually use phase modulation

but searching for FM how to will probably be more useful than PM

i know you can recreate a lot of subtractive sounds with FM but it is neither intuitive nor easy

i could make a square or a saw... but don't even know where to start to modulate the pulse width
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21st February 2011
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No filters is rather obvious; instead of starting with a block and chopping away everything you don't want you start with a blank piece of paper and add everything you do want.

While it's possible to get pulse or square-ish sounds out of it, I think PWM is not going to be one of 'm - mainly because they've been very stingy with the LFOs. You could for instance fake PWM with a sample-based synth by crossfading between a 10%, 25% and 50% pulsewave; and you could try to use a similar approach on the DX. But - there's only one LFO.

Fourier series - Wikipedia, the free encyclopedia is also an option

The cheapest square is like this: choose algorithm 9 ( http://cnx.org/content/m19841/latest/Fig4_14.png ) and modulate operator 3 tuned at 1:1 with operator 4 tuned at 2:1. Modulation amount is around 30. That nets you a hollow square sound. It gets better when you add operator 5, tuned at 4:1, modulating operator 3, amount also around 30.
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22nd February 2011
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Akh
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22nd February 2011
Old 22nd February 2011
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Quote:
Originally Posted by Yoozer View Post
No filters is rather obvious; instead of starting with a block and chopping away everything you don't want you start with a blank piece of paper and add everything you do want.
That strikes me as a description of additive synthesis, not FM synthesis.

In the context of subtractive synthesis, I would describe FM synthesis as being similar to patching an LFO in to the frequency cut-off of a filter... with an LFO that is oscillating at such a great speed its rise and fall aren't perceived, as an entirely new timbre arises from the process. There's a little more to it than that, but that's how I'd think of it in the context of subtractive synthesis.

Well, that's my two cents.

Anyhow, there's info about simulating PWM on a FM synth here.
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22nd February 2011
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Quote:
Originally Posted by Akh View Post
Anyhow, there's info about simulating PWM on a FM synth here.
That only works if you have a flexible enough FM matrix, such as in FM8. A DX7 won't be able to do what that link mentions.
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22nd February 2011
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I actually got a reasonable PWM sound on a Casio VZ-10M, the waveform resembled a square/pulse wave and everything. I don't believe it's possible to do that on a DX7, or even a TG77, as it depends on the specific oddities of the VZ's saw wave.

The main thing about FM that causes analog users to become frustrated is that it can't really make the sort of broad spectrum you get from saw/square waves. Feedback helps with this, but only to a certain extent. There are many other ways to make interesting sounds, so there's no reason to get hung up on that.
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22nd February 2011
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While I'd rather use an analogue synth for the typical PWM sounds, it is perfectly possible to program them on the DX7. I can offer an audio clip of the DX7 MkI PWM sound. Note that I used the LFO for pitch modulation to demonstrate that you don't even need to use it for PWM.
Attached Files
File Type: mp3 DXpwm.mp3 (1.78 MB, 213 views)
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22nd February 2011
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Quote:
Originally Posted by Akh View Post
That strikes me as a description of additive synthesis, not FM synthesis.
Well, what are you doing with FM synthesis, then? You start with a sinewave and add sidebands

Sure - it's not "pure" additive as in "here's 1024 harmonics, have fun" but pretty additive otherwise.
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22nd February 2011
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Quote:
Originally Posted by Akh View Post
In the context of subtractive synthesis, I would describe FM synthesis as being similar to patching an LFO in to the frequency cut-off of a filter... with an LFO that is oscillating at such a great speed its rise and fall aren't perceived, as an entirely new timbre arises from the process.

.
In that example your still adding sidebands rather than subtracting. Just because you do it on a "subtractive" synth is irrelevant.
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22nd February 2011
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DX7 Frequency Modulation synthesis...... would be the last place I'd go for PWM sounds, in exactly the same way that a 909 wouldn't be the place I'd go for real drum sounds.
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22nd February 2011
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I would actually be tempted to go to the DX7 for more exotic PWM sounds, just like I'd go for the 909 for more exotic drum sounds.
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22nd February 2011
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Don't even try to apply subtractive synthesis programming to an FM synth, they do not correlate.
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22nd February 2011
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Quote:
Originally Posted by The Real MC
Don't even try to apply subtractive synthesis programming to an FM synth, they do not correlate.
This is not always true. You can set a canvas for subtractive synthesis on the DX7 and then apply the typical subtractive tricks. For example, you can create two rich waveforms, even something like saw, pulse or triangle, set certain filter behaviour (resonant/non-resonant/LP/BP or totally unheard before) and then detune the waveform generators, use amp and filter envelopes, modulate, etc.

The results will not sound 100% like your Moog synthesizer but they will be similar. Of course, there is also the whole world of non-subtractive sounds to explore. FM is full of surprises and I'd suggest to try everything and experiment as much as possible.

I agree that in order to do subtractive on the DX7 you need to know FM first and this is completely different from subtractive, haha. Don't get me started on additive, wave sequencing and formant synthesis using the DX7.

Quote:
Originally Posted by Jordan15
Does anyone know how to:

1. Make the sine into more of a square wave, and

2. What you'd have to do with the modulator to give the original carrier sine wave a PWM sound. My best guess would be some kind of LFO with the modulator, but I don't know if LFO can be applied to single operators or not.
1. Carrier to Modulator freq ratio = 1:2

2. As above but put a low fixed freq operator between the Carrier and the main Modulator and add some feedback to the modulator on top. Algo 4 is perfect for that.

There are other possibilities that create a different sounding PWM effect. FM is a bitch to write about on forums, get experimenting now :-)

Quote:
Originally Posted by Yoozer
While it's possible to get pulse or square-ish sounds out of it, I think PWM is not going to be one of 'm - mainly because they've been very stingy with the LFOs. You could for instance fake PWM with a sample-based synth by crossfading between a 10%, 25% and 50% pulsewave; and you could try to use a similar approach on the DX. But - there's only one LFO.
A fixed frequency modulator acts as an LFO. You get 1 global and 4 independent LFOs in the DX7 (4 not 6, because a modulator without a carrier is like sound in outer space).
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23rd February 2011
Old 23rd February 2011
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Quote:
Originally Posted by MuOdyssey View Post
A fixed frequency modulator acts as an LFO. You get 1 global and 4 independent LFOs in the DX7 (4 not 6, because a modulator without a carrier is like sound in outer space).
Well, you can get 5 "LFOs" if you use algos 16 - 18. But you'd just get a weird warbling sine wave.
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23rd February 2011
Old 23rd February 2011
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Haha, that's correct. I'm sure there is a use for a weird warbling sine. Perhaps for the ambient noises of the starship Voyager.
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