Re: [AUDITORY] Ear Probe Mics and detecting the heartbeat? (Anders Tornvig Christensen )

Subject: Re: [AUDITORY] Ear Probe Mics and detecting the heartbeat? From: Anders Tornvig Christensen <atc@xxxxxxxx> Date: Mon, 1 Jul 2013 09:22:59 +0200 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY> --------------090507030004050303060607 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Hello Sam, I measured the noise floors of some microphones in the ear canal a couple of months ago, so I inevitably picked up some heartbeats. To measure the heartbeat in the ear canal you pay attention to microphone and preamp specifications below, say, 100 Hz. The self-noise must be low enough and the sensitivity must be high enough. Be aware that broadband noise specifications in A-weighted dB tell very little about what the noise is at the lowest frequencies. The microphone does not _need_ to go all the way down to 1-5 Hz. If I highpass filter my recordings at 50 Hz (I only measured myself with some mics), I can still vaguely hear the beat every ~1 s. Much energy is in the 10-30 Hz band, so your microphone needs to accommodate that at least. Above 100 Hz you start to hear breathing. I used the ER-7C for something else some time ago. I would expect its noise floor to be way too high for quality heartbeat measurements, and its response starts rolling off at 200 Hz. You could look in the direction of the ER-10C or ER-10B+ instead; they are reasonable for this purpose. Finally, consider whether a microphone in the ear canal is the best way to record the heartbeat. Regards, Anders Tornvig PhD student in acoustics Aalborg University, DK On 06/28/2013 12:36 PM, Jelfs, Sam wrote: > > Dear List, > > Just a question for those of you with experience using ear probe > microphones, do you ever hear the heartbeat? I've built a couple of > in-ear microphones, and can hear my own heartbeat, but the quality is > relatively poor, and only works in very low-noise conditions. I was > looking in to using dedicated probe mics, such as Etymotic ER-7C > (http://www.etymotic.com/pro/er7c-ts.aspx) and whether that might give > me a better signal-to-noise ratio, but just wondered if anyone has any > experience of this before I buy some. > > Thanks > > Sam Jelfs > > -------------------------------------------------- > > Sam Jelfs > > Research Scientist > > Philips Research Laboratories, Eindhoven > > Smart Sensing & Analysis > > Address : High Tech Campus 36 > > 5656 AE Eindhoven > > The Netherlands > > Tel: +31 (0)40 27 42402 > > e-Mail: sam.jelfs@xxxxxxxx > > > ------------------------------------------------------------------------ > The information contained in this message may be confidential and > legally protected under applicable law. The message is intended solely > for the addressee(s). If you are not the intended recipient, you are > hereby notified that any use, forwarding, dissemination, or > reproduction of this message is strictly prohibited and may be > unlawful. If you are not the intended recipient, please contact the > sender by return e-mail and destroy all copies of the original message. --------------090507030004050303060607 Content-Type: text/html; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit <html> <head> <meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type"> </head> <body text="#000000" bgcolor="#FFFFFF"> <div class="moz-cite-prefix">Hello Sam, I measured the noise floors of some microphones in the ear canal a couple of months ago, so I inevitably picked up some heartbeats. To measure the heartbeat in the ear canal you pay attention to microphone and preamp specifications below, say, 100 Hz. The self-noise must be low enough and the sensitivity must be high enough. Be aware that broadband noise specifications in A-weighted dB tell very little about what the noise is at the lowest frequencies. The microphone does not _need_ to go all the way down to 1-5 Hz. If I highpass filter my recordings at 50 Hz (I only measured myself with some mics), I can still vaguely hear the beat every ~1 s. Much energy is in the 10-30 Hz band, so your microphone needs to accommodate that at least. Above 100 Hz you start to hear breathing. I used the ER-7C for something else some time ago. I would expect its noise floor to be way too high for quality heartbeat measurements, and its response starts rolling off at 200 Hz. You could look in the direction of the ER-10C or ER-10B+ instead; they are reasonable for this purpose. Finally, consider whether a microphone in the ear canal is the best way to record the heartbeat. Regards, Anders Tornvig PhD student in acoustics Aalborg University, DK On 06/28/2013 12:36 PM, Jelfs, Sam wrote: </div> <blockquote cite="mid:17233_1372479988_51CE61F4_17233_40_1_2457CAAB54A05440B0CE80D0D831099E36332CBD@xxxxxxxx" type="cite"> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <style>  </style> <div class="WordSection1"> Dear List,   Just a question for those of you with experience using ear probe microphones, do you ever hear the heartbeat? I’ve built a couple of in-ear microphones, and can hear my own heartbeat, but the quality is relatively poor, and only works in very low-noise conditions. I was looking in to using dedicated probe mics, such as Etymotic ER-7C (<a moz-do-not-send="true" href="http://www.etymotic.com/pro/er7c-ts.aspx">http://www.etymotic.com/pro/er7c-ts.aspx</a>) and whether that might give me a better signal-to-noise ratio, but just wondered if anyone has any experience of this before I buy some.   Thanks   Sam Jelfs   --------------------------------------------------   Sam Jelfs Research Scientist Philips Research Laboratories, Eindhoven Smart Sensing & Analysis   Address : High Tech Campus 36 5656 AE  Eindhoven The Netherlands Tel: +31 (0)40 27 42402 e-Mail: <a class="moz-txt-link-abbreviated" href="mailto:sam.jelfs@xxxxxxxx">sam.jelfs@xxxxxxxx</a>   </div> <hr> The information contained in this message may be confidential and legally protected under applicable law. The message is intended solely for the addressee(s). If you are not the intended recipient, you are hereby notified that any use, forwarding, dissemination, or reproduction of this message is strictly prohibited and may be unlawful. If you are not the intended recipient, please contact the sender by return e-mail and destroy all copies of the original message. </blockquote> </body> </html> --------------090507030004050303060607--

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Electrical Engineering Dept., Columbia University