|
Dear Zhao, Reverberation can be modeled in many ways,
and the way in which this is done affects its sensitivity to various factors
that affect real room reverberation. Perhaps the simplest (and a very useful) approach
to modeling reverberation is to use the theory developed by Sabine (and refined
by others). Sometimes called ‘statistical’ room acoustics, that
type of approach allows one to predict reverberation time from room volume and total
acoustic absorption. It also allows one to predict sound pressure level at a
given distance from the source (consisting of the sum of direct and diffuse
field contributions). Students (and others) often forget that reverberation
time is only half the story in characterizing room acoustics in this way –
a small room with a reverb time of 0.5 s sounds completely different to a large
room with the same reverberation time. That difference is reasonably well
described, to a first order, by the sound pressure level prediction. For this
reason, it is important that things like source-receiver distance and room
volume accompany reverberation time in simply describing a room acoustical environment. With regard to your first question, using Norris-Eyring’s
formula provides a quick estimation that can be used in preparing a simulation.
However, such equations assume diffuse field reverberation, which may not be a
good match for the situation being modeled. Of course such theory does not account for
many phenomena, such as the pattern of early reflections (which can be modeled
in common simulation software), room modes, occlusion & diffraction
effects, effect of proximity to large surfaces, spatial characteristics of the
soundfield, coupled room phenomena... There is so much to discuss here, it
would probably be better to read some textbook chapters on room acoustics. If
you are particularly interested in simulation, Vorlaender’s Auralization
could be one to consider. Hope this helps densil From: AUDITORY -
Research in Auditory Perception [mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Zhao LiHeng Dear lists,
Recently, I was reading papers about speech separation
in the reverberant environment. Generally speaking, most of the previous works
are carried on simulated data, in which the reverberant speech is the
convolution of a clean speech and the simulated room impulse response provided
by some toolkits, such as Roomsim (given by D. R. Campbell). However, it is
surprising to me that the reverberation time can be set to a certain value
(e.g. RT60 = 300ms) in some papers. As I know, reverberation time is influenced
by many factors, such as room volume, absorption coefficient of the surfaces et
al. Therefore, I have the following questions:
1. How
to set the reverberation time to be a certain value in a simulated room? Is
there any paper or toolkit for performing it? 2. If
the other factors are invariable, how much will the reverberation time change
according with the location variances of source or microphone? Is the
reverberation time mainly determined by room configuration? Thanks for your answers and discussions! Liheng Zhao |