Re: Reverberation time (Densil Cabrera )

Subject: Re: Reverberation time From: Densil Cabrera <d.cabrera@xxxxxxxx> Date: Sun, 19 Jul 2009 20:52:55 +1000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY> This is a multi-part message in MIME format. ------_=_NextPart_001_01CA085F.12605C9D Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Dear Zhao, =20 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. =20 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. =20 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. =20 Hope this helps densil =20 ________________________________ From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxx On Behalf Of Zhao LiHeng Sent: Sunday, 19 July 2009 7:47 PM To: AUDITORY@xxxxxxxx Subject: Reverberation time =20 Dear lists, =20 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 =3D 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? =20 Thanks for your answers and discussions! =20 Liheng Zhao =20 =20 =20 ------_=_NextPart_001_01CA085F.12605C9D Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable <html xmlns:v=3D"urn:schemas-microsoft-com:vml" = xmlns:o=3D"urn:schemas-microsoft-com:office:office" = xmlns:w=3D"urn:schemas-microsoft-com:office:word" = xmlns=3D"http://www.w3.org/TR/REC-html40"> <head> <meta http-equiv=3DContent-Type content=3D"text/html; = charset=3Dus-ascii"> <meta name=3DGenerator content=3D"Microsoft Word 11 (filtered medium)">  <title>Mail</title> <style>  </style> </head> <body lang=3DEN-US link=3Dblue vlink=3Dpurple leftmargin=3D5 = topmargin=3D5 #ffffff> <div class=3DSection1> Dear = Zhao,<o:p></o:p> <o:p> </o:p> 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.<o:p></o:p> <o:p> </o:p> 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.<o:p></o:p> <o:p> </o:p> 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.<o:p></o:p> <o:p> </o:p> Hope this = helps<o:p></o:p> densil<o:p></o:p> <o:p> </o:p> <div> <div class=3DMsoNormal align=3Dcenter style=3D'text-align:center'> <hr size=3D2 width=3D"100%" align=3Dcenter tabindex=3D-1> </div> From: = AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxx = On Behalf Of Zhao LiHeng Sent: Sunday, 19 July = 2009 7:47 PM To: = AUDITORY@xxxxxxxx Subject: Reverberation = time<o:p></o:p> </div> <o:p> </o:p> <div> Dear lists,<o:p></o:p> </div> <div>   <o:p></o:p> </div> <div>   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 =3D 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:<o:p></o:p> </div> <div>   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?<o:p></o:p> </div> <div>   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?<o:p></o:p> </div> <div>   <o:p></o:p> </div> <div>   Thanks for your answers and = discussions!<o:p></o:p> </div> <div>   <o:p></o:p> Liheng Zhao<o:p></o:p>  <o:p></o:p>  <o:p></o:p> </div> <div>  <o:p></o:p> </div> </div>  </body> </html> ------_=_NextPart_001_01CA085F.12605C9D--

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