Subject: Re: envelope extraction From: Daniel TAFT <DTAFT@xxxxxxxx> Date: Tue, 24 Feb 2009 12:28:27 +1100 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>This is a multi-part message in MIME format. ------_=_NextPart_001_01C9961F.3160EABC Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Hi Ben, =20 One example of envelope based auditory processing is the cochlear implant. Envelopes are usually extracted from bandpass filter outputs by full-wave rectification and low pass filtering. If it's any use to you, the filter cutoff frequency commonly used for this is 200 Hz. (And some experimental CI processing strategies have used half-wave rectification without any smoothing at all). I'm not sure if there is a neural modeling or physiological reason for the cutoff frequency. 200 Hz retains the temporal modulations of the speech envelope, which some CI listeners are able to hear as a cue to fundamental frequency. =20 As you say, in normal hearing, neurons can follow much higher frequency stimuli. Although it's not exactly my area, I would assume you would only use a low (e.g. 50 Hz) cutoff frequency if you wanted to model auditory processing without temporal cues. For a physiological model, I don't know of any reason for 50 Hz. In addition to neural refractory effects, there are lowpass cutoff frequencies related to the synaptic delay and re-sequestering of neuro-transmitter by the inner hair cells. But that too is much faster, I think.=20 =20 Sorry I don't have any references. Maybe someone else can comment. =20 Regards, Daniel Taft =20 ________________________________ From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxx On Behalf Of Hornsby, Benjamin Wade Young Sent: Tuesday, 24 February 2009 3:55 AM To: AUDITORY@xxxxxxxx Subject: [AUDITORY] envelope extraction Hi all, I hope the answer to this question is not too obvious but,... We have recently been talking about auditory processing models, in specific, temporal processing models, many of which incorporate an envelope extraction stage. To do this I've seen in many cases the use of half wave rectification followed by a low pass filter. The cutoff for this filter is generally a pretty low frequency, say around 50 Hz or so. A colleague suggested that the actual cutoff frequency should be based on the assumed time constant of the system or subsystem being evaluated. I've been trying to determine the physiologic rational for such a low frequency filter (slow time constant) in models of auditory processing. Neural processing limitations like the refractory period of the neuron are much faster than this. Anyone have a reference or two that might help explain the physiologic rational for this low frequency filter cutoff? =20 Thanks much, =20 Ben =20 =20 ------_=_NextPart_001_01C9961F.3160EABC Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML xmlns=3D"http://www.w3.org/TR/REC-html40" xmlns:o =3D=20 "urn:schemas-microsoft-com:office:office" xmlns:w =3D=20 "urn:schemas-microsoft-com:office:word"><HEAD> <META http-equiv=3DContent-Type content=3D"text/html; = charset=3Dus-ascii"> <META content=3D"MSHTML 6.00.6000.16788" name=3DGENERATOR> <STYLE>@xxxxxxxx Section1 {size: 8.5in 11.0in; margin: 1.0in 1.25in 1.0in = 1.25in; } P.MsoNormal { FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman" } LI.MsoNormal { FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman" } DIV.MsoNormal { FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman" } A:link { COLOR: blue; TEXT-DECORATION: underline } SPAN.MsoHyperlink { COLOR: blue; TEXT-DECORATION: underline } A:visited { COLOR: purple; TEXT-DECORATION: underline } SPAN.MsoHyperlinkFollowed { COLOR: purple; TEXT-DECORATION: underline } SPAN.EmailStyle17 { COLOR: windowtext; FONT-FAMILY: Arial; mso-style-type: personal-compose } DIV.Section1 { page: Section1 } </STYLE> </HEAD> <BODY lang=3DEN-US vLink=3Dpurple link=3Dblue> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2>Hi Ben,</FONT></SPAN></DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2></FONT></SPAN> </DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = size=3D2><FONT=20 face=3DArial color=3D#0000ff>One example of envelope based auditory = processing is=20 the cochlear implant. Envelopes are usually extracted from bandpass = filter=20 outputs by full-wave rectification and low pass filtering. If it's = any use=20 to you, the filter cutoff frequency commonly used for this is 200 Hz. = (And=20 s</FONT></FONT></SPAN><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2>ome experimental CI processing strategies have = used=20 half-wave rectification without any smoothing at all).=20 </FONT></SPAN></FONT></SPAN><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2>I'm not sure if there is a neural modeling = or=20 physiological reason for the cutoff frequency. 200 Hz retains = the=20 temporal modulations of the speech envelope, which some CI listeners are = able to=20 hear as a cue to fundamental frequency.</FONT></SPAN></DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2></FONT></SPAN> </DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2>As you say, in normal hearing, neurons can = follow much=20 higher frequency stimuli. Although it's not exactly my area, I = would assume=20 you would only use a low (e.g. 50 Hz) cutoff frequency if you wanted to = model=20 auditory processing without temporal cues. </FONT></SPAN><SPAN=20 class=3D442005922-23022009><FONT face=3DArial color=3D#0000ff = size=3D2>For a=20 physiological model, I don't know of any reason for 50 Hz. In = addition to=20 neural refractory effects, there are lowpass cutoff frequencies = related to=20 the synaptic delay and re-sequestering of neuro-transmitter by the = inner=20 hair cells. But that too is much faster, I think. = </FONT></SPAN></DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2></FONT></SPAN> </DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2>Sorry I don't have any references. Maybe = someone else can=20 comment.</FONT></SPAN></DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2></FONT></SPAN> </DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2>Regards,</FONT></SPAN></DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2>Daniel Taft</FONT></SPAN></DIV> <DIV dir=3Dltr align=3Dleft><SPAN class=3D442005922-23022009><FONT = face=3DArial=20 color=3D#0000ff size=3D2></FONT></SPAN> </DIV><BR> <DIV class=3DOutlookMessageHeader lang=3Den-us dir=3Dltr align=3Dleft> <HR tabIndex=3D-1> <FONT face=3DTahoma size=3D2><B>From:</B> AUDITORY - Research in = Auditory Perception=20 [mailto:AUDITORY@xxxxxxxx <B>On Behalf Of </B>Hornsby, Benjamin = Wade=20 Young<BR><B>Sent:</B> Tuesday, 24 February 2009 3:55 AM<BR><B>To:</B>=20 AUDITORY@xxxxxxxx<BR><B>Subject:</B> [AUDITORY] envelope=20 extraction<BR></FONT><BR></DIV> <DIV></DIV> <DIV class=3DSection1> <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20 style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Hi = all,<o:p></o:p></SPAN></FONT></P> <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20 style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">I hope the answer to this = question=20 is not too obvious but,… We have recently been talking about = auditory processing=20 models, in specific, temporal processing models, many of which = incorporate an=20 envelope extraction stage. To do this I’ve seen in many cases the = use of half=20 wave rectification followed by a low pass filter. The cutoff for this = filter is=20 generally a pretty low frequency, say around 50 Hz or so. A colleague = suggested=20 that the actual cutoff frequency should be based on the assumed time = constant of=20 the system or subsystem being evaluated. I’ve been trying to = determine the=20 physiologic rational for such a low frequency filter (slow time = constant) in=20 models of auditory processing. Neural processing limitations like the = refractory=20 period of the neuron are much faster than this. Anyone have a reference = or two=20 that might help explain the physiologic rational for this low frequency = filter=20 cutoff?<o:p></o:p></SPAN></FONT></P> <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20 style=3D"FONT-SIZE: 10pt; FONT-FAMILY: = Arial"><o:p> </o:p></SPAN></FONT></P> <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20 style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Thanks=20 much,<o:p></o:p></SPAN></FONT></P> <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20 style=3D"FONT-SIZE: 10pt; FONT-FAMILY: = Arial"><o:p> </o:p></SPAN></FONT></P> <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20 style=3D"FONT-SIZE: 10pt; FONT-FAMILY: = Arial">Ben<o:p></o:p></SPAN></FONT></P> <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20 style=3D"FONT-SIZE: 10pt; FONT-FAMILY: = Arial"><o:p> </o:p></SPAN></FONT></P> <P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20 style=3D"FONT-SIZE: = 12pt"><o:p> </o:p></SPAN></FONT></P></DIV></BODY></HTML> ------_=_NextPart_001_01C9961F.3160EABC--