Timbre perception

Slide 1:Timbre perception

Slide 2:Objective

Timbre perception and the physical properties of the sound on which it depends Formal definition: �that attribute of auditory sensation in terms of which a listener can judge two sounds similarly presented and having the same loudness and pitch as being dissimilar.�

Slide 3:Timbre

Related to musical instrument / object recognition To distinguish between the same note played on different instruments perceived quality of a sound Some sound quality descriptors: mellow, rich, harsh, shrill etc. Judgments of timbre � subjective

Slide 4:Timbre

Pitch and loudness � related to the physical properties of frequency and amplitude � may be considered as one dimensional attributes of sound � can be ordered on a single scale � pitch (from low to high); loudness (from quiet to loud) Timbre is a multidimensional attribute of sound � no single scale along which we can order the timbre of sounds

Slide 5:Timbre

Timbre depends on: Spectral envelope � patterning of energy as a function of frequency Temporal properties � fluctuations over time

Slide 6:Spectral envelope

A major determinant of timbre Overall distribution of energy over frequency e.g. Strong lower harmonics � �dark�, �mellow� e.g. Strong higher harmonics � �bright�, �shrill� More specifically timbre is related to the relative level in each critical band rem: The critical bandwidth variation with frequency � this dscribes the spectral analysis carried out by the ear.

Slide 7:Spectral envelope

In a complex sound the partials are described as either resolved (lower components) or unresolved (high components) by the auditory system. Resolved and unresolved - related to the critical bands Timbre depends on whether most of the energy lies in resolved or unresolved components.

Slide 8:Spectral envelope example

The effect of spectrum on timbre � asa demo 28, trk 53 � recognise the musical instrument Listen and note the following: the point where you can identify each sound the point where recognition of the sound becomes unambiguous

Slide 9:Temporal properties

Timbre recognition may also depend on: whether a sound is periodic; waveform changes over time; spectral changes over time; preceding and following sounds (e.g. masking). The frequency components in a sound change over time - described by the temporal envelope Attack (onset) � increase in amplitude Steady state Decay portion (offset) � amplitude decreases

Slide 11:Temporal envelope

Diagram � indicates different attacks for a plucked vs. a bowed violin string, also speech sounds �ba� �wa� have different attacks Plucked strings � attack followed by decay the onsets (attacks) of sounds can be used to identify them � recognition depends strongly on onsets and temporal structure of sound envelope

Slide 12:Effect of temporal envelope

Piano tone � rapid onset and gradual decay Effect of temporal envelope in timbre perception - asa demo 29 (trk 54-56) Chorale played on piano and recorded Chorale played from end to beginning and recorded The recording of the backward chorale is played out in reverse � causing each note to be reversed in time.

Slide 14:Effect of temporal envelope

Reversed piano tone � completely different timbre � no longer sounds like a piano Spectral energy distribution is unchanged by this time reversal temporal envelope changed

Slide 15:Some instruments have noise like qualities that influence their perceived timbre At the start of a flute note Important for the synthesis of a convincing flute sound To create a realistic synthesis of a sound � spectral envelope and the variation in time of the components � some harmonics may have different time envelopes

Slide 16:Some timbre measures

Spectral centroid � related to the subjective �brightness� of a sound - measures the frequency at which the energy of the sound is centred.

Slide 17:Tristimulus

a measure of tone colour, calculates the proportion of energy in the fundamental, mid and high frequency components Tristimulus1 � the amplitude of the first harmonic divided by the sum of all the amplitudes of all the harmonics Tristimulus2 � the sum of the amplitudes of the 2-4th harmonics divded by sum of all amplitudes Tristimulus3 � sum of amplitdues from the 5th upwards divided by the sum of all the amplitudes

Slide 18:Irregularity

variation in energy between the partials A value close of zero � indicates little variation between the amplitudes of adjacent frequency components A value close to 1 � large difference in amplitude between adjacent frequency components

Slide 19:Next masking and sound localisation