Equalizer adjustments at specific frequencies produce predictable perceptual shifts in timbre

Evidence

A related and important area of signal processing to filtering is equalization. Unlike filtering, equalization is not interested in removing frequency components but in selectively boosting, cutting or reducing them to achieve a desired effect. The process of equalization can be modeled as a process of adding or subtracting a filtered version of the signal from the signal, as shown in Figure 7.40. Adding the filtered version gives a boost to the frequencies selected by the filter, whereas subtracting the filtered output reduces the frequency component amplitudes in the filter’s frequency range. The filter can be a simple highor low-pass filter, which results in a treble or bass tone control, or it can be a band-pass filter to give a bellshaped response curve. The cutoff frequencies of the filters may be either fixed or variable depending on the implementation. In addition, the bandwidths of the band-pass filters and, less commonly, the slopes of the highand low-pass filters can be varied. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2419 (#expands, via linked claim)

For pure sine waves, however, the sensitivity to change is markedly different and is a strong function of both amplitude and frequency. For example, at 1 kHz, the just-noticeable amplitude change varies from 3 dB at 10 dB(SPL) to 0.3 dB at 80 dB(SPL). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 648 (#corroborates, via linked claim)

Categorization

• XREF: connects to: Equalization adjusts sound by perceived timbre, not measured accuracy; Signal processing compensates reproduction deviations through equalization; Reduced playback levels cause timbral shifts and lost low bass (+4 more)

Broader Connections

• Filtering alters timbre, but nearby spectral boosting can partially offset the loss #expands (0.85)
• Equalization selectively boosts or cuts frequencies rather than removing them #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2419
• Auditory sensitivity varies nonuniformly across the frequency range #corroborates (0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 648