Re: formant filtering

[Eckard Blumschein <Eckard.Blumschein@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

At 21:45 27.02.2003 -0500, Ramdas Kumaresan wrote:
>Alain de Cheveigne pointed me to the following.
>
>de Cheveigné, A. (1999). Formant bandwidth affects the identification
>of competing vowels. Proc. ICPhS, 2093-2096, available as:
>http://www.ircam.fr/pcm/cheveign/ps/icphs99.pdf

This paper starts with the words: 'Formant bandwidth is known to have
little effect on the quality or intelligibility of isolated vowels'. 
Look at Fig.1. Don't worry about Hz instead of kHz. Narrowing of bandwidth
made about 12 dB(A) more difference between peaks and inter-formant valleys
as compared with widening. So the observed effect on mutual masking is
bound to a basic assumption: Both competing vowels have the same RMS. 

This difficulty to have an adequate basis for comparison reminds me of own
experience. We tried to use spectral smearing for mitigation of an annoying
highly tonal noise which was caused from a pulsed arc due to precise power
electronic switching. The method can avoid dangerous mechanical resonance.
We were also able to make the acoustic noise less 'cutting'. However, this
required to randomize frequency over a considerable range of deviation from
its technologically required mean value. We achieved a satisfactory
decrease of tonality only on condition this range exceeded the critical
bandwidth, while in this case the noise did perhaps not get less annoying
but, as expected, even louder.

Eckard