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Re: Reference for typical SNRs is public spaces

Dear List,
Since we’re assuming Andy is asking about speech-to-noise ratio when referring to SNR in public spaces, I wondered if the question couldn’t be answered by back-of-the-envelope calculations using some assumptions and articulation index theory (AI). 
It turned out there was quite a long list of assumptions behind the calculation (see below), but the resultant simple calculation yielded a SNR of 0.5 dB, which is quite in line with the values other posters have indicated may actually be present. Two other facts became apparent as I did this, however, and further motivate my posting.
First, the long list of assumptions makes apparent the long list of influences on the SNR in such a situation. These influences need to be characterized in any attempt to generalize from SNR measurements in a given scenario, a fact other posters have alluded to.
Second, it is important to note that much work has been done recently to model or empirically characterize these influences on speech intelligibility, and that, while the models may require more computational power than found on the back of an envelope, they are no problem to execute on current laptop computers. The implication is that it should not be very difficult to determine a reasonably-accurate distribution of SNRs over wide variation in the assumed listening scenario without any measurements.
Bill Woods, PhD
Principal Research Scientist | Starkey Hearing Research Center
2150 Shattuck Ave. | Suite 408 | Berkeley, CA 94704-1345
T: 510-845-4876 x 14
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The assumptions are:
  1. Talkers have no hearing loss and no cognitive loss.
  2. The talkers are facing each other and speaking in their “mother tongue”.
  3. We know the percent-correct (%C) targeted by the talkers and it is less than 100% (it’s a challenging environment).
  4. We know the nature of the speech in such a conversation, from a low-context vs. high-context perspective.
  5. The talkers are within their critical distance (i.e., ignore reverberation of talkers’ speech).
  6. We know the long-term spectral shape of speech at the eardrums.
  7. We know the long-term spectral shape of noise at the eardrums.
  8. The noise is stationary.
  9. The noise is diffuse.
  10. The diffuse noise in combination with diotic direct-wave target speech generates the equivalent of an “internal” wideband binaural SNR improvement of ~1.0 dB over monaural listening.
  11. Overall level is not too high (i.e., no “roll-over” effect for intelligibility has occurred).
  12. We’re not including lip reading.
These assumptions allow one to, first, determine the AI needed to achieve the assumed target %C given the assumed type of speech, and, second, determine the SNR required with the assumed spectral shapes to obtain that AI.
For instance, assuming talkers want 95%C with “unfamiliar sentences” then using the polynomial fits from Sherbecoe and Studebaker (JASA 1990) of the ANSI S3.5-1969 transfer functions between AI and %C, our talkers would need an AI of 0.45. If we assume the noise and speech have the same long-term spectral shape then the SNR can be determined from (SNR+12)/30=0.45 (staying with the 1969 AI method), yielding SNR = 1.5 dB.  Subtracting the binaural SNR improvement yields 0.5 dB. 
From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Andy Sabin
Sent: Wednesday, January 22, 2014 9:53 AM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Reference for typical SNRs is public spaces
Hi List, 
Can anyone point me to a reference showing SNRs that are typically observed in public spaces (e.g., restaurants, bars ...etc)? I can find this info for overall SPL, but am having a hard time finding it for SNR. 
Andy Sabin