cross modulation vs ring modulation ??

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eeprom_one
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cross modulation vs ring modulation ??

Post by eeprom_one » Fri Apr 11, 2008 5:51 am

i try to get the concepts, can you help me?

a lot of thks
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Post by Big Gnome » Fri Apr 11, 2008 7:19 am

Cross modulation is a periodic variation in frequency, ring modulation is a periodic variation in amplitude. They're essentially the same as vibrato and tremolo, respectively, except that the carrier in a cross- or ring mod configuration are modulated by audio-rate signals.
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Post by ipassenger » Fri Apr 11, 2008 10:57 am

I think it depends somewhat on the naming convention of the manufacturer, quite often (on my waldorf pulse for example) Cross Mod refers to the interplay between two pulse waves.

If both input waves are in the positive position the output (or cross mod) signal is in the negative,

if both input waves are in the negative position the output is also negative,

all other situations where one of the input waves is positive and the other is negative the output is positive.

It is in essence the same as an 'exlusive-or gate'. When the Osc are at different frequencies complex wave shapes are formed.

It sounds similar to ring mod and very similar indeed to ring mod-ding to pulse waves but it isn't quite. The reason is that by modulating one wave with the other in cross mod, it is effictively modulating its amplitude and polarity much like ring mod does.

The cross mod Big Gnome described is more commonly referred to as frequency modulation.

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Post by nathanscribe » Fri Apr 11, 2008 12:42 pm

ipassenger's description above also applies to the Korg MS20. It uses the XOR method to generate its ring-mod, fed by pulse waves.

I read somewhere that Ring Mod takes its name from the diode ring originally used in these circuits; another theory is that it comes from the way the frequencies are distributed at the output (equidistant from the one input frequency, the gap determined by the other). Don't know the truth of it.

Not many devices use the old method; most employ dedicated multiplier ICs, some use OTAs, some are discrete - the old diode arrangement is the simplest, and sounds good too.

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Post by meatballfulton » Fri Apr 11, 2008 1:09 pm

The important thing to remember whether it's FM, AM, ring mod or crossmod you are generating sideband frequencies that are not harmonically related to the carrier or modulator. The most common use is to create metallic sounds because in nature, struck metal objects (bells, gongs, etc.) typically have non-harmonic overtones.

If you carefully detune the carrier and modulator to specific ratios, you can also create harmonic sounds that have a different overtone series than saws and squares...that is the basis behind FM synthesis as in the Yamaha DX synthesizers.

Ring modulation is just amplitude modulation with the carrier absent from the output.

With AM if the carrier frequency is F1 and the modulator frequency is F2, the output frequencies will be:

F1-F2, F1, F1+ F2

With ring modulation the outputs will be F1-F2, F1+F2.

The amplitude of the sidebands vs. the carrier increases with modulation depth. Typically ring modulators on synths are set for maximum modulation by default, while cross-mod depth is usually controllable.
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Post by ipassenger » Fri Apr 11, 2008 1:09 pm

Nathan,

Oh right.. I had patched up a X-mod and pulse wave ring mod on my nord modular and figured they weren't the same despite sounding very similar.. Maybe i patched it wrong or maybe there is a calc error in the nord which produces slightly different results. If i remember rightly the differences were only apparent at certain freq ratios. I might repeat the test and see if i can work out what the difference is, or find out that my memory kidding me. :)

Cross Mod vs Ring Mod:

Cross Mod:

Produces richer tones than ring mod if simple waves are used (sine etc) as the output is the sum and difference of pulse (Squ) waves which contain masses of harmonics.

Ring Mod:

It tends to be more useful as it can receive any signal and work on the fundamentals and harmoincs present in both, so in a way it is a lot more versatile. With ringmod u can modulate a saw with a tri or a complex FM waveform with a drum beat and potentially still get useable results the cross mod is unlikely to work to well when converting a compplex waveform into a binary pulse pattern.

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Post by V301H » Fri Apr 11, 2008 6:26 pm

Cross-mod is similar to DX-7-style FM where one oscillator modulates another oscillator at a set ratio. It was the advent of cheap super-stable digital oscillators that made the DX-7 possible where FM could produce consistent results and you could have enough oscillators for complex sounds. In a VCO analog synth the Oscillators are not as stable and can't maintain a precise frequency ratio so the resulting sounds tend to be discordant. If you have a DCO synth with Cross-Mod capabilities you can get more musical-sounding results. The number of analog oscillators needed to do complex DX-7-style FM would be prohibitively expensive and that's why we don't see any analog FM synths.

Ring Modulation is a bit different in that the output is the sum and difference of two input frequencies. In a typical analog synth the RM input would be two oscillators whose frequencies can be varied as desired. None of the input frequencies are present at the output so you get discordant sounds which may sound similar to Cross-Mod. In a typical stand-alone Ring Modulator you have an internal oscillator which can be set at a desired frequency. The second input can be almost any pitched sound from a keyboard, guitar, or other instrument. The Ring-Modulated sound can be blended with the input to add harmonics not found in the original sound. As an example, Jon Lord of Deep Purple ran his Hammond organ through a Ring Modulator. This added new harmonics to the organ sound and could make it sound fatter and somewhat discordant as he varied the settings on his RM.
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Post by nathanscribe » Fri Apr 11, 2008 6:33 pm

There are other interesting variations on the implemetation of RM on various synths.

As I mentioned earlier, the Korg MS uses the pulse waves from its two VCOs, one on each input of the XOR, which they call ring mod. The Yamaha CS series do it a different way, and one input of the modulator consists of a mix of the VCOs, or an ouput from one of the filters or VCAs (depending on which CS we're talking about) - the other input to the modulator is a dedicated oscillator, which has (as previously described) a speed control, a depth control - and, on some of the CS synths, you can modulate the speed of the modulation (!) with an envelope generator (typically just attack and decay countour). Very useful, and sounds mad.

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Post by eeprom_one » Sat Apr 12, 2008 2:11 am

V301H wrote:Cross-mod is similar to DX-7-style FM where one oscillator modulates another oscillator at a set ratio. It was the advent of cheap super-stable digital oscillators that made the DX-7 possible where FM could produce consistent results and you could have enough oscillators for complex sounds. In a VCO analog synth the Oscillators are not as stable and can't maintain a precise frequency ratio so the resulting sounds tend to be discordant. If you have a DCO synth with Cross-Mod capabilities you can get more musical-sounding results. The number of analog oscillators needed to do complex DX-7-style FM would be prohibitively expensive and that's why we don't see any analog FM synths.

Ring Modulation is a bit different in that the output is the sum and difference of two input frequencies. In a typical analog synth the RM input would be two oscillators whose frequencies can be varied as desired. None of the input frequencies are present at the output so you get discordant sounds which may sound similar to Cross-Mod. In a typical stand-alone Ring Modulator you have an internal oscillator which can be set at a desired frequency. The second input can be almost any pitched sound from a keyboard, guitar, or other instrument. The Ring-Modulated sound can be blended with the input to add harmonics not found in the original sound. As an example, Jon Lord of Deep Purple ran his Hammond organ through a Ring Modulator. This added new harmonics to the organ sound and could make it sound fatter and somewhat discordant as he varied the settings on his RM.
which is the correct?
ipassenger wrote:Nathan,

Oh right.. I had patched up a X-mod and pulse wave ring mod on my nord modular and figured they weren't the same despite sounding very similar.. Maybe i patched it wrong or maybe there is a calc error in the nord which produces slightly different results. If i remember rightly the differences were only apparent at certain freq ratios. I might repeat the test and see if i can work out what the difference is, or find out that my memory kidding me. :)

Cross Mod vs Ring Mod:

Cross Mod:

Produces richer tones than ring mod if simple waves are used (sine etc) as the output is the sum and difference of pulse (Squ) waves which contain masses of harmonics.

Ring Mod:

It tends to be more useful as it can receive any signal and work on the fundamentals and harmoincs present in both, so in a way it is a lot more versatile. With ringmod u can modulate a saw with a tri or a complex FM waveform with a drum beat and potentially still get useable results the cross mod is unlikely to work to well when converting a compplex waveform into a binary pulse pattern.
thk u very much for the answer :wink:
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Post by eeprom_one » Sun Apr 13, 2008 5:42 pm

V301H wrote:Cross-mod is similar to DX-7-style FM where one oscillator modulates another oscillator at a set ratio. It was the advent of cheap super-stable digital oscillators that made the DX-7 possible where FM could produce consistent results and you could have enough oscillators for complex sounds. In a VCO analog synth the Oscillators are not as stable and can't maintain a precise frequency ratio so the resulting sounds tend to be discordant. If you have a DCO synth with Cross-Mod capabilities you can get more musical-sounding results. The number of analog oscillators needed to do complex DX-7-style FM would be prohibitively expensive and that's why we don't see any analog FM synths.

Ring Modulation is a bit different in that the output is the sum and difference of two input frequencies. In a typical analog synth the RM input would be two oscillators whose frequencies can be varied as desired. None of the input frequencies are present at the output so you get discordant sounds which may sound similar to Cross-Mod. In a typical stand-alone Ring Modulator you have an internal oscillator which can be set at a desired frequency. The second input can be almost any pitched sound from a keyboard, guitar, or other instrument. The Ring-Modulated sound can be blended with the input to add harmonics not found in the original sound. As an example, Jon Lord of Deep Purple ran his Hammond organ through a Ring Modulator. This added new harmonics to the organ sound and could make it sound fatter and somewhat discordant as he varied the settings on his RM.
This is the correct answer, the ring modulation offers on it output the sum and difference of two input frecuencies.

thks :wink:
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