Adding lower-frequency sound can decrease perceived sharpness

Evidence

However, if the upper cut-off. frequency at 1 kHz is kept constant and the noise is widened downward to produce a band between 200 Hz and 1 kHz, sharpness decreases. This means that sharpness can be decreased by adding sound at lower frequencies. This is an effect that - at least at first glance - may be unexpected. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1350

When the lower cut-off frequency is shifted towards lower values and the noise is changed into a uniform exciting noise, sharpness decreases markedly in agreement with psychoacoustical results. It remains, however, clearly above that of the I-kHz tone. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1361

The sharpness of a narrow-band noise at 1 kHz to which more noise is added at higher frequencies to produce a spectral width from 1 to 10 kHz, increases from 1 acum to about 2.5 acum. This effect might be expected because adding more noise might increase the sharpness. However, if the upper cut-off. frequency at 1 kHz is kept constant and the noise is widened downward to produce a band between 200 Hz and 1 kHz, sharpness decreases. This means that sharpness can be decreased by adding sound at lower frequencies. This is an effect that - at least at first glance - may be unexpected. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1350

Categorization

• XREF: Ties to the signal-vs-ground asymmetry in the soundscape chapters: low-frequency ‘masking’ content reshapes perceptual judgments rather than merely adding to them. — connects to: Turning down volume suppresses perceived bass and treble relative to midrange — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 626; Adding higher partials can drop the perceived pitch of a tone — Eric J. Heller, Why You Hear What You Hear- An…, 2067; Tactile vibration raises perceived loudness and lowers preferred bass levels — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1826
• QUESTION: The symmetry with loudness models is worth chasing: does shifting cut-off frequency affect sharpness just via the moment’s center-of-gravity location, or does g(z) do real work here?
• DEFINE: Establishes acum as the unit of sharpness and shows the asymmetric effect of spectral widening — a concrete empirical anchor for the sharpness concept.
• corroborated: 4 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1350; Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1361

Broader Connections

• Turning down volume suppresses perceived bass and treble relative to midrange #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 626
• Adding higher partials can drop the perceived pitch of a tone #corroborates (0.75) — Eric J. Heller, Why You Hear What You Hear- An…, 2067