The perceptual salience of several outstanding features of quasiharmonic, time-variant spectra was investigated in musical instrument sounds. Spectral analyses of sounds from seven musical instruments (clarinet, flute, oboe, trumpet, violin, harpsichord, and marimba) produced time-varying harmonic amplitude and frequency data. Six basic data simplifications and five combinations of them were applied to the reference tones: amplitude-variation smoothing, coherent variation of amplitudes over time, spectral-envelope smoothing, forced harmonic-frequency variation, frequency-variation smoothing, and harmonic-frequency flattening. Listeners were asked to discriminate sounds resynthesized with simplified data from reference sounds resynthesized with the full data. Averaged over the seven instruments, the discrimination was very good for spectral envelope smoothing and amplitude envelope coherence, but was moderate to poor in decreasing order for forced harmonic frequency variation, frequency variation smoothing, frequency flattening, and amplitude variation smoothing. Discrimination of combinations of simplifications was equivalent to that of the most potent constituent simplification. Objective measurements were made on the spectral data for harmonic amplitude, harmonic frequency, and spectral centroid changes resulting from simplifications. These measures were found to correlate well with discrimination results, indicating that listeners have access to a relatively fine-grained sensory representation of musical instrument sounds.

The perceptual salience of several outstanding features of musical instrument quasi-harmonic time-variant spectra were investigated. These are: amplitude spectrum shape variation, harmonic amplitude (or frequency) micro-variations, spectral envelope irregularity, harmonic frequency incoherence, and frequency inharmonicity. Seven musical instrument sounds (clarinet, flute, oboe, trumpet, violin, harpsichord, and marimba) were spectrum-analyzed to produce time-varying harmonic amplitude and frequency data. Tones resynthesized from these data were equalized in pitch, loudness, and duration. Six basic data simplifications were applied together with five combinations of them: amplitude versus time smoothing, spectrum shape fixing, spectral envelope smoothing, harmonic frequency coherence, frequency versus time smoothing, and harmonic frequency fixing. Twenty subjects participated in a discrimination study to determine the ease of distinguishing sounds synthesized from simplified data from sounds resynthesized from the full data. Averaged over the seven instruments, the mean discrimination scores were: spectral envelope smoothing, 96%; spectrum shape fixing, 91%; harmonic frequency fixing, 71%; frequency smoothing, 70%; frequency coherence, 69%; and amplitude smoothing, 66%. In conclusion, spectral envelope smoothing had a profound effect (discrimination >95%) for all instruments except the trumpet. Spectrum shape fixing, which eliminates any spectral centroid variation, had a very large effect except for the clarinet and the oboe.