FM feedback - Kyma Forum

Tips & Techniques

FM feedback

Post New Topic Post A Reply
profile | register | preferences | faq | search

next newest topic | next oldest topic

Author	Topic: FM feedback
JohnCowan Member	posted 29 November 2000 09:45 I've been looking into FM synth design and have been a bit stumped about how to feedback an oscillator's signal as shown in various books about FM. I tried CTRL dragging and dropping and only succeded in creating a copy of the oscillator as the modulator. I noticed in the Kyma sound library one of the sounds used the feedback module pair to do this but it introduces a delay. Altho, it is only a few samples, I am wondering if this alters the effect. Does anyone have any other suggestions or assurance? I understand phase modulation accomplishes similar effects as FM. I haven't tried it yet. Does anybody have experience with this technique? Thanks, John IP: Logged
SSC Administrator	posted 29 November 2000 18:31 John -- There are a couple of examples of feedback FM in the "Synthesis-Keyboard Controlled" folder in the file called "Distortion Synthesis KBD". IP: Logged
Graham Breed Member	posted 30 November 2000 16:12 I couldn't find any examples. Exactly which sounds use them? I did get it working myself with a feedback pair, and it sounds much the same as what a DX synth does. You do need a fair bit of delay to get a clean sound. There are problems with legato playing, as the new note inherits the old one's modulator, or something. Also, I can't get it to work with a polyphonic MIDI mapper. Ah, hang on, it seems to be the ones that say "feedback" or "fdbk" that have feedback in them. Who'd a thought it? And they do work polyphonically. I'll have a proper look at them tomorrow. [This message has been edited by Graham Breed (edited 30 November 2000).] IP: Logged
gelauffc Member	posted 01 December 2000 06:39 Real FM is not supported in Kyma! If you use an oscilator, enable modulation and give it a modulation index, it sounds like FM but it actually is PHASE modulation! Prove: Take an AR envelope generator (lineair!) for modulator. If it would be FM the pitch of the oscilator would go up during attack and stay there until the release where the pitch would go down. FM sounds the same as PM, because the power spectrum will be the same (assuming sine waves are used as oscilators/mods). The difference is in the phase of the harmonics. I think it is due to implementation isues that PM is chosen instead of FM. I think it would be an nice addition to Kyma to have actual FM or PM operators with feedback. I played with an old Yamaha FB-01 once, which could feedback one of his operators. It really sounds cool. If interested, I could write some C++ code program that implements something simmular. But it would be nice know that there is some interest for this. IP: Logged
pete Member	posted 04 December 2000 15:31 Hi All I thought that FM on the DX7 was realy PM as it worked by reading different points on a looped wave table, and that if the modulater was always a sine wave that it would work just like true FM but with a 90 deg phase shift. [This message has been edited by pete (edited 04 December 2000).] IP: Logged
gelauffc Member	posted 05 December 2000 06:41 I think your are right pete. IP: Logged
SSC Administrator	posted 05 December 2000 09:10 quote: Originally posted by gelauffc: Prove: Take an AR envelope generator (lineair!) for modulator.... FM sounds the same as PM, because the power spectrum will be the same (assuming sine waves are used as oscilators/mods). The difference is in the phase of the harmonics. And if you paste the AR into the Frequency field of the Oscillator and add it to the carrier frequency, you will hear FM. The disadvantage of FM is that the modulation index depends on the frequency of the modulator (not simply on its amplitude). So if you have a constant c/m ratio and control the carrier pitch from a keyboard, you would get different spectra on each pitch. In PM, the modulation index is related to the just the amplitude of the modulator and so is the same no matter what the carrier frequency. IP: Logged
kelvin Member	posted 05 December 2000 09:17 I know that Yamaha uses John Chownings method which they bought the rights to. And that was why no one else came out with it as the main synthesis on any of there synths. Casio did use PM. And Korg came out with one synth after Nippon Goki (or something like that) bought Korg, and they already owned Yamaha. Making them, Nippon, the parent Co. So some technolgy was shared. Also like vector synthesis, which Yamaha got from it's purchase of Sequential, making SY and TG 33, etc and Korgs Wavestation shown at the same NAMM show. Kelvin IP: Logged
pete Member	posted 06 December 2000 11:30 Hay Kelvin I've always wondered about the history. where did New England digital's Synclavier II FM synth fit into the story ?? Did they have connections with john chowning in some way. Although thier method was mostly harmonic sine wave additive , it did have one and only one sinewave modulator. IP: Logged
gelauffc Member	posted 07 December 2000 07:42 quote: Originally posted by SSC: And if you paste the AR into the Frequency field of the Oscillator and add it to the carrier frequency, you will hear FM. The disadvantage of FM is that the modulation index depends on the frequency of the modulator. In PM, the modulation index is related to the just the amplitude of the modulator and so is the same no matter what the carrier frequency. Do not forget to tell the samplingrate of the modulator(AR) is reduced to 1kHz and therefore if we would have pasted a sinewave in the freq. field (+carr. freq) the modulation frequency should be well below 500 Hz. I am not saying that this would not be interesting! FM versus PM: "MI only related to Amp" is a strong point to go for PM! Implementing PM is also much easier. IP: Logged
kelvin Member	posted 10 December 2000 09:57 quote: Originally posted by pete: Hay Kelvin I've always wondered about the history. where did New England digital's Synclavier II FM synth fit into the story ?? Did they have connections with john chowning in some way. Although thier method was mostly harmonic sine wave additive , it did have one and only one sinewave modulator. That's a good question Pete. The Synclavier was out long before the DX-7. And as I remember was based on additive and FM originally. So perhaps it sliped in. Kelvin IP: Logged

All times are CT (US)	next newest topic \| next oldest topic
Administrative Options: Close Topic \| Archive/Move \| Delete Topic

Contact Us | Symbolic Sound Home

This forum is provided solely for the support and edification of the customers of Symbolic Sound Corporation.

Ultimate Bulletin Board 5.45c