CI Atlas · Hearing Music Through an Implant · Module 02

2The Building Blocks: Pitch, Timbre and Rhythm

Pitch, timbre and rhythm are the acoustic dimensions of music, and how the normal ear hears them is the yardstick for judging electric hearing.

FPitch: the basis of melody and harmony

Pitch is the perceptual correlate of a sound's fundamental frequency and is the dimension that lets us order notes from low to high, the raw material of melody and harmony. The healthy cochlea encodes pitch two ways at once: place coding, where each frequency excites a specific tonotopic location along the basilar membrane, and temporal coding, where the timing of neural firing follows the waveform. Most melodic information in music sits in fundamentals below roughly 500-1000 Hz, the region where temporal cues to pitch are strongest in normal hearing. Musical pitch is judged in fine steps: trained listeners discriminate changes of about one semitone, and a melody is recognised by tracking the direction and size of these small steps.[2004][2007][2009]

TTimbre: why a violin is not a trumpet

Timbre, or tone colour, is what distinguishes two instruments playing the same note at the same loudness, and it lets us tell a violin from a trumpet instantly. Timbre arises from the spectral envelope, the pattern of relative strengths of the harmonics above the fundamental, which differs characteristically between instruments. The attack, the onset transient at the start of a note, is a second major timbre cue, and a sharp percussive attack such as a piano's is far more recognisable than a slow-building one. Because normal-hearing listeners confuse instruments mainly within a family (a trumpet for a trombone), their errors stay structured in a way that reveals how finely timbre is normally resolved.[2009][2004]

The normal ear encodes pitch two ways at once. Place coding uses the cochlea’s tonotopy: each frequency from roughly 20 Hz at the apex to 20 kHz at the base peaks at its own position, so pitch is a map of place. Temporal coding carries pitch in the precise timing of nerve firing, which phase-locks to the waveform up to a few kHz. A cochlear implant offers a coarse place map across a handful of electrodes and almost no usable temporal pitch, which is why fine melody is so hard to restore. Schematic.

Every one of these instruments plays the same middle C: the fundamental sits at 261.6 Hz and the harmonics fall on its integer multiples (523, 785, 1046 Hz and so on). What your ear hears as flute versus violin versus clarinet is the spectral envelope — the relative height of those harmonics. The implant smears this fine spectral detail across a few broad channels, which is why instruments lose their character even when the melody survives. Switch instruments to watch the envelope change while the pitch stays put. Illustrative.

TRhythm, tempo, and building tunes over time

Rhythm is the temporal pattern of a piece, the arrangement of note durations and accents that unfolds over seconds rather than the millisecond-scale timing that carries pitch. Tempo is the overall pace, the rate of the underlying beat, and together rhythm and tempo give music its drive and its recognisable shape independent of any notes. Melody is built by stringing pitches in time into a contour, a sequence of rises and falls, while harmony stacks pitches simultaneously into chords. Recognising a song therefore fuses two clocks at once: the slow rhythmic frame and the fine pitch sequence, and the normal ear tracks both effortlessly, setting the standard electric hearing must meet.[2004][2007]

Case 29.2 · The Building Blocks

A musician asks you to explain, before her implant is activated, what parts of music she should expect to hear. She wants to know which acoustic features carry melody, which carry the identity of her cello, and which carry the beat.

Which acoustic dimension primarily lets a listener tell a cello from a flute playing the same note?

Self-assessment — Module 23 questions

Question 1

The perceptual correlate of a note's fundamental frequency, and the basis of melody, is:

Question 2

Most melodic information in music lies in fundamentals in which range?

Question 3

In normal hearing, what two mechanisms together encode pitch?

Tracked locally in your browser — see /progress for the dashboard.