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I was studying the musical theory and an idea came to me - what happens if I play dissonant chords at the same time, but one of them being panned to the extreme left and the other one - to the extreme right?

I tried that in my DAW, setting one piano to play the C chord and the other one to play the Dm chord at the same time. Obviously the sound is very dissonant. Then I panned one piano to the extreme left and the other one - to the extreme right and the dissonance was gone! I heard both C and Dm but they were not in "conflict" any more. The sound is unusual, but there are no beatings and it feels like it's around me (i.e. no defect or penalty from extreme panning when both pianos sound at the same time). And it definitely has a mood to it. I even created a small melody based on this effect..

This fact seems like it belongs to its own area of musical harmony but I cannot find any significant mention of it (aside from some credit from the binaurals establishment but these guys are not really into music).

My question is - is there a known area of musical theory that studies this kind of music? Are there any known musical pieces that employ this kind of "harmony"?

noncom
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  • Were you listening with headphones or speakers? – Robert Harvey Jun 27 '16 at 00:02
  • @RobertHarvey as of now I only had the opportunity to listen on headphones – noncom Jun 27 '16 at 00:07
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    C and Dm are somewhat consonant; it would be interesting to repeat the test with C and C#, which is dissonant by any standard. – No'am Newman Jun 27 '16 at 04:21
  • @No'amNewman well... I tried that just now. I can't really describe what I hear except that the sound is very tingy (probably coz it's piano) and has some dark quality to it. I can't say that it sounds dissonant to me. Rather I would characterise it as of being very very dark in timbre. No beatings as well. Probably a skilled musician would characterize it as being dissonant, but to me - beatings are gone, the conflict is dissolved.... the sound, though, remains.. but it is whole now, no sense of fragility that usually accompanies the beatings. – noncom Jun 27 '16 at 21:14

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I don't know of any published studies on this, but the basic cause is well known, and it is a fundamental limitation on the quality of sound reproduction.

When you pan the two chords hard left and right, your two loudspeakers (or earphones) are acting as two independent (monophonic) sound sources. Human hearing is very good at locating the position of different sound sources, so it will "interpret" this as two independent sounds, and tend to ignore the fact that they are at different pitches.

But if you pan both chords to the center, each loudspeaker is trying to reproduce both of them. Since the amplifiers and speakers are not perfect, this will create a certain amount of "intermodulation distortion", which generates frequencies that were not supposed to be there. (Note, this is a completely different effect from the audible perception of "beats" and "difference tones" which are artefacts of the way your ears and brain work. Intermodulation distortion is real, in the sense that you can measure it objectively with a microphone and a frequency analyser.)

If you attempt to play two pure tones with frequencies f1 and f2, intermodulation distortion creates unwanted tones at frequencies like 2f1-f2, 2f2-f1, etc. If f1 and f2 correspond to notes a semitone apart (say E from your C chord and F from your Dmin) these will be approximately (but not exactly) E flat and F sharp. It should be clear that the end result of this sort of distortion may sound like be a rather dissonant mess!

Intermodulation distortion between the notes of just one (consonant) chord is less of a problem. If you take a major chord like C E G C, then (in just intonation) the frequencies of the notes are in the ratios 4: 5: 6: 8. Any intermodulation distortion will also produce simple integer ratios which are usually just more consonant tones. For example C and E will produce 2x5-4 = 6 = G and 2x4-5 = 3 = G an octave lower. (Of course for an instrument like a piano that is not tuned in just intonation, the details are a bit messier, but the overall result is similar).

This is one reason why high-quality sound reproduction of complex sounds uses as many independent audio channels as possible.

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    There's a bit more to it than this. Given two sound sources panned hard left and hard right, headphones do not mix the two tones in the air *at all,* nor does the sound from one earpiece reach the other ear. Further, any other panning arrangement will mix the two sounds in the electronics, which doesn't occur in a hard pan scenario. – Robert Harvey Jun 27 '16 at 00:04
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    Very interesting exposition on the physics aspect of the subject. It should be pointed out that the same intermodulation phenomenon is what makes notes closer to each other on a (for example) piano tending towards sounding dissonant (not just on the electronic devices and because of their imperfection). – José David Jun 27 '16 at 00:10
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    Also, describing the "beats" phenomena as a neurological artifact is perhaps misleading. They result from the fact that when the intermodulating frequencies are very close to each other, some resulting interference frequencies are very low and fall below the threshold of frequency that the human hear perceives as a frequency and stars to hear as a modulated sound. So the neurology of the human hearing device is certainly part of the explanation of the phenomenon, but the "beats" do exist physically, they are not created in any way by our brain or ears. – José David Jun 27 '16 at 00:14
  • I'm almost positive the effect you mention is not audible by humans. – dbanet Jun 27 '16 at 14:34
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First of all congrats to the OP for an intriguing and innovative idea.

I don't know of any specific studies about this subject either, but I think that the reason why the two chords don't sound dissonant when separated left and right is the same as when they are separated by an octave, and the reason why (traditionally) we have 9th, 11th chords and not 2nd, and 4th (unless suspended) chords: pitches very close to each other tend to be more dissonant, but the same pitch class of the dissonant note played in a different octave does not sound so dissonant anymore. It seems like the ear separation provides the same effect.

If you play a C 13th chord without the 7th, you get the sames notes as in the described experiment, C-E-G-D-F-A, except that the last three notes are in the above octave in relation to the base C.

I've done the experiment too in a DAW and the two combinations sound pretty similar harmonically to me. I may be under suggestion, though, so evaluation by the community would be useful, here's a clip with the two sounds played sequentially (C-E-G on the left side together with D-F-A on the right side, followed by centered C-E-G-D-F-A, D-F-A an octave above).

José David
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C and Dm are both diatonic chords in C major. That is not dissonant. That consists of the notes C D E F G and A. That is what you might call a cluster.

What you are experiencing is not some kind of auditory illusion; It is a physical phenomena. Beat frequencies are real things. They occur when two tones (or harmonics of tones) interact. If they are sufficiently close to each other a beat frequency can be heard (audio range) or perceived (heard as pulses).

When each tone is played in separate ear pieces then each wave does not interfere with each other and thus does not create beat frequencies.

When the frequency of two notes are close together, the beat frequency can sound like unpleasant, or if the beat frequency is low enough: a pulsing of the sound or an envelope on the volume, a tremolo effect. At this point the beat frequency would be too low to hear itself and the amplitude modulation/tremolo effect would be all that could be heard.

That said, it is also possible to perceive the beat frequency that would be made if two tones were played together, if the two tones are played separately in each ear. This is called a binaural beat. It's easy to imagine that such an effect that is produced inside our own mind would be less prominent than the actual beat frequency, were the two tones/sounds played together and heard monophonically.

Andrew Gallasch
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