Portamento and Amplitude Modulation synthesis

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briandc
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Portamento and Amplitude Modulation synthesis

Post by briandc » Wed Mar 27, 2019 10:57 am

Hi everyone,
two quick questions: is there a specific name for the type of portamento that changes its rate depending on the distance between the two notes? (usually slower rate when the interval is higher)

Also, does anyone know off-hand of any hardware synths that were made especially for amplitude modulation? I'd like to find some audio demos if possible.

Thanks!

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Re: Portamento and Amplitude Modulation synthesis

Post by meatballfulton » Wed Mar 27, 2019 3:13 pm

Two kinds of portamento:

constant rate: time increases as distance between notes increases

constant time: time stays the smae regardless of distance between notes

To do amplitude modulation, route an audio rate oscillator (could be an LFO) to modulate the amplifier. Listing every possible synth that can do this would take a long time. I'm not sure what you meant by "made especially for amplitude modulation" but the most obvious would be pretty much any modular synth.

True AM sounds like ring modulation but contains the original carrier frequency as well as the generated sideband frequencies.
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Re: Portamento and Amplitude Modulation synthesis

Post by madtheory » Wed Mar 27, 2019 3:23 pm

The Kawai K1 uses AM.

I know you didn't ask for this, but the Casio VZ-1 allows either constant rate or constant time portamento. I don't know of any other hardware synths like that. It also allowed 48 semitones of pitch bend and, if memory serves, a different inerval for upwards bend versus downward bend. I could never understand why this isn't more common. It's as if keyboard designers never heard of inversions.

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Re: Portamento and Amplitude Modulation synthesis

Post by briandc » Wed Mar 27, 2019 5:44 pm

meatballfulton wrote:Two kinds of portamento:

constant rate: time increases as distance between notes increases

constant time: time stays the smae regardless of distance between notes

To do amplitude modulation, route an audio rate oscillator (could be an LFO) to modulate the amplifier. Listing every possible synth that can do this would take a long time. I'm not sure what you meant by "made especially for amplitude modulation" but the most obvious would be pretty much any modular synth.

True AM sounds like ring modulation but contains the original carrier frequency as well as the generated sideband frequencies.
Thanks for the help with the portamento bit! (might be good to add to the glossary..?)

As for AM, are there really that many synths that allow one oscillator to modulate another (except for modulars, of course) ? I guess I thought that most synths only allow to mix oscillator signals together, without cross-modulating..?

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Re: Portamento and Amplitude Modulation synthesis

Post by briandc » Wed Mar 27, 2019 5:55 pm

madtheory wrote:The Kawai K1 uses AM.

I know you didn't ask for this, but the Casio VZ-1 allows either constant rate or constant time portamento. I don't know of any other hardware synths like that. It also allowed 48 semitones of pitch bend and, if memory serves, a different inerval for upwards bend versus downward bend. I could never understand why this isn't more common. It's as if keyboard designers never heard of inversions.
Thanks madtheory. I've never used/owned a VZ-1, but I agree that there are certain, nice control options that seem to have never "taken off," such as separate settings for pitch bend up/down, constant rate/constant time, LFO retrig/freeflow, etc.. I guess that only makes some synths more "desirable" than others, if/when those specific features are needed.

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Re: Portamento and Amplitude Modulation synthesis

Post by Broadwave » Thu Mar 28, 2019 10:04 am

In addition, there are two other aspects attached to Portamento - Log and Linear glide.

Linear portamento has a straight linear speed from one note to the next - The Minimoog and many digital synths use this type of glide.

With Log portamento, the glide speed decreases as you reach the target note - Most analogue synths use this.

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Re: Portamento and Amplitude Modulation synthesis

Post by briandc » Thu Mar 28, 2019 3:05 pm

Broadwave wrote:In addition, there are two other aspects attached to Portamento - Log and Linear glide.

Linear portamento has a straight linear speed from one note to the next - The Minimoog and many digital synths use this type of glide.

With Log portamento, the glide speed decreases as you reach the target note - Most analogue synths use this.
This is new to me! Thanks Broadwave! :)

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Re: Portamento and Amplitude Modulation synthesis

Post by meatballfulton » Fri Mar 29, 2019 2:58 pm

briandc wrote:As for AM, are there really that many synths that allow one oscillator to modulate another (except for modulars, of course) ? I guess I thought that most synths only allow to mix oscillator signals together, without cross-modulating..?
Oscillator modulating oscillator: FM, "cross mod"

Oscillator modulating amplifier: AM, ring mod
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