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Viewing topic "Subtractive Synth Filters vs FM Synth Modulators and LFO’s?"

     
Posted on: August 18, 2017 @ 07:48 PM
lastmonk
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status: Experienced

Here are three novice-still-learning it all questions basically about timbre on synths.

What is the practical difference between the function of the Filter in subtractive synthesis, vs the modulator in FM synthesis?

Since both are used to manipulate the harmonics or overtones (timbre) of a sound, aren’t they essentially different ways of achieving the same thing?  Or put another way aren’t the same timbres possible from both given that the sound sources are roughly equal?

What is the functional difference between modulations of LFO’s that have been routed to the filter on a subtractive synth and the modulations that are applied to a tone on a FM synth?

I’m just starting to scratch the surface on the whole subject matter of additive, vs, subtractive, vs granular vs hybrid synthesis.  And when it comes to playing with the timbre of a sound, some of this stuff seems like six of one, half a dozen of the other.  I do understand that they all take different roads, but it seems like they all end up in the same place.  And it seems like they’re all restrained by the physics of pitch, frequency, amplitude, and harmonics and that at the end of day, additive vs subtractive vs granular vs hybrid synthesis is just a matter of subjective preference from the musician’s POV.

Am I wrong here?  Can anyone clarify?  Or point me to a good source that will say why one of these is better than the other?

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Posted on: August 19, 2017 @ 04:05 PM
meatballfulton
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Modulating a filter with an LFO merely changes the cutoff frequencey. Assuming a LPF, you would hear the sound cycle betwen darker and brighter.

Modulating the amplitude of the modulator in FM would do something similar. But modulating the frequency of the modulator would create a different harmonic series, typically it would cycle between metallic timbres with the “normal” timbre only when the LFO wave is at it’s zero point.

I’d suggest googling for FM tutorials that walk you through creating some cliche sounds on a DX7.

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Posted on: August 20, 2017 @ 07:38 PM
lastmonk
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meatballfulton - 19 August 2017 04:05 PM

Modulating a filter with an LFO merely changes the cutoff frequencey. Assuming a LPF, you would hear the sound cycle betwen darker and brighter.

Modulating the amplitude of the modulator in FM would do something similar. But modulating the frequency of the modulator would create a different harmonic series, typically it would cycle between metallic timbres with the “normal” timbre only when the LFO wave is at it’s zero point.

I’d suggest googling for FM tutorials that walk you through creating some cliche sounds on a DX7.

Thanx, I this clears some of this up for me.

But I’m also under the assumption that the filter on the Motif also changes the harmonic series, or overtones.  Is that true?

I was told that the filter on the motif, plays the same role as the modulator on an FM synth is that true?

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Posted on: August 22, 2017 @ 05:26 AM
meatballfulton
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Filters are relatively blunt instruments. They can remove harmonics above the cutoff point (LPF), below the cutoff point (HPF) or outside a band centered at the cutoff point (BPF).

Let’s look at the harmonic series for A440, multiply the fundamental by a series of integers: 1, 2, 3, 4, 5, 6....:

440, 880, 1320, 1760, 2200, 2640....

Note that some are octaves: 880, 1760

Some are fifths: 1320, 2640

Or thirds: 2200

and so on. Each is at a lower amplitude than the harmonic preceding it (i.e. fundamental is strongest)and the series is infinite, but soon the amplitude falls to inaudibility as the frequencies increase to beyond human hearing.

This gets technical really fast. I first learned about the harmonic series in high school physics class, when we studied the vibrations of strings and pipes. This has direct application to programming synth sounds.

What filters cannot do is remove individual harmonics in the series as you see fit, something you can do with a Hammond organ...the drawbars represent the first nine steps of the harmonic series. So a Hammond can produce this series:

440, 1320, 1760, 2200

but a single filter cannot. If you had filters capable of very narrow bandpasses, you could sculpt out individual harmonics but you would need as many filters as the harmonics you wish to remove.

A filter also cannot shift the frequencies of the harmonic series, the way a ring modulator (really amplitude modulation) or FM can. If I feed a ring modulator the A440 series with a modulaor tone at 100, I would get the sums and differences of the two frequencies:

340, 540, 780, 980, 1220, 1420, etc.

Note that this is not a standard harmonic series any more! The resulting sound would be very metallic and out of tune. Try this with the ring mod effect on your Motif and hear it for yourself.

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Posted on: August 22, 2017 @ 06:56 PM
lastmonk
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Joined  12-17-2013
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meatballfulton - 22 August 2017 05:26 AM

Filters are relatively blunt instruments. They can remove harmonics above the cutoff point (LPF), below the cutoff point (HPF) or outside a band centered at the cutoff point (BPF).

Let’s look at the harmonic series for A440, multiply the fundamental by a series of integers: 1, 2, 3, 4, 5, 6....:

440, 880, 1320, 1760, 2200, 2640....

Note that some are octaves: 880, 1760

Some are fifths: 1320, 2640

Or thirds: 2200

and so on. Each is at a lower amplitude than the harmonic preceding it (i.e. fundamental is strongest)and the series is infinite, but soon the amplitude falls to inaudibility as the frequencies increase to beyond human hearing.

This gets technical really fast. I first learned about the harmonic series in high school physics class, when we studied the vibrations of strings and pipes. This has direct application to programming synth sounds.

What filters cannot do is remove individual harmonics in the series as you see fit, something you can do with a Hammond organ...the drawbars represent the first nine steps of the harmonic series. So a Hammond can produce this series:

440, 1320, 1760, 2200

but a single filter cannot. If you had filters capable of very narrow bandpasses, you could sculpt out individual harmonics but you would need as many filters as the harmonics you wish to remove.

A filter also cannot shift the frequencies of the harmonic series, the way a ring modulator (really amplitude modulation) or FM can. If I feed a ring modulator the A440 series with a modulaor tone at 100, I would get the sums and differences of the two frequencies:

340, 540, 780, 980, 1220, 1420, etc.

Note that this is not a standard harmonic series any more! The resulting sound would be very metallic and out of tune. Try this with the ring mod effect on your Motif and hear it for yourself.

Awesome!!!!  Thanx.,.  this gives me something to chew on for a while!!!!

Cheers

  [ Ignore ]  


 
     


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