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In most styles of music low notes seemed to be spaced more sparsely in pitch than high ones ie. a piano piece might have octaves in the left hand and dense melody in the right hand.

This spacing is in keeping with the spacings of the harmonic series, if I play a bass note then I get a similar distribution by picking out its harmonics. However, without reference to any starting pitch, playing a third in the bass sounds a lot less distinct and well defined than playing one in a higher register.

I was musing that this could have something to do with the logarithmic nature of pitch vs. the linear hz value. As if the bass notes have fewer hz between them, so sound more bunched together - but what mechanism would cause this? Is it purely in the ear, or does it involve a physical effect before hearing?

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The point of consonant intervals (of which chords are mostly comprised) is that the various frequencies are in a ratio of small numbers. Now if the intervals are perfect intervals, the result is a combined signal that has the frequency of the greatest common divisor of all contained frequencies, reminiscent (after frequency separation in the inner ear) of a lower frequency with a particular overtone composition.

Now the most transparent reception occurs when the virtual fundamental frequency is actually in the hearable range and most of the purported and their real overtones are in the most trained and discriminative part of the hearing, namely in the meaning-carrying frequencies for human speech, the vowel formants.

That explains why there is a preferred range for chords to be in. However, the perceived muddiness also very much depends on the instrument in question. Upright pianos suffer quite a bit from "disharmonicity" in their lower range, making even single low notes sound muddy. A guitar is written one octave higher than it is actually played, yet guitar chords tend to maintain character reasonably well for chords not written all that different. Similar for organ pipes. Low chords with organ pipes or large recorders tend not to sound muddy as much as hollow since they not just have rather pure overtones but also comparatively few of them.

But even instruments like accordion or harmonium which have numerous but pure overtones tend to work better with chords than upright pianos. Grand pianos with their comparatively longer strings and thus lower disharmonicity tend to behave more gracefully when venturing into the lower ranges.

So basically there are both rather abstract psychoacoustic reasons for the muddiness of low chords as well as some instrument-related causes depending on the instrument's overtone composition and disharmonicity.

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Pitches in lower registers have harmonics which are more easily discernible to our hearing. When two or more low notes are heard together, each will produce their own set of harmonics which will tend to clash. Thus muddy. Higher pitches will also produce harmonics, but they won't be heard so easily, and won't be so discordant with each other.

  • This seems like an educated guess that doesn't ring true to me. It seems more likely to me that psychoacoustic reconstruction of missing fundamentals, frequency masking, and loudness differences based on frequency are more likely contributing to the "muddiness". A-220 sounds fine in chords and we can easily hear its first 10 harmonics and beyond. (the tenth being only 2200 Hz, which is almost an octave below the typical hearing limit for young humans) – Todd Wilcox Oct 8 '15 at 14:42

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