Re: Fw: sursound: speaker phones (Erick Gallun )

Subject: Re: Fw: sursound: speaker phones
From:    Erick Gallun  <gallun(at)SOCRATES.BERKELEY.EDU>
Date:    Wed, 25 Oct 2000 13:59:05 -0700

At 02:44 PM 10/25/00 -0500, James W. Beauchamp wrote: >While we're on the subject of sound localization, can someone explain >why speaker phones always sound like you're "talking through a tube" to >the person on the other end of the line? ... >Here is a related problem: [...] When I am >actually there listening, the speech is as clear as a bell; I ignore >all environmental sounds and echoes. [...] Later, when I play it back >through the headphones, >the basic sound is there, but now the echos and environmental sounds swamp >out the speaker, who is rendered barely audible. As a hearing researcher who has recently (last year) lost all hearing in one ear, this is a question with which I am very much concerned. Now that I no longer have the use of my binaural system to segregate sounds in the environment, the echoes and noise around me cause great interference with both detection and identification of sounds. In a quiet, non-reverberant environment I don't even notice the loss. In a crowded room or on the street however, I can barely have a conversation. However, it does sound better than a speaker phone. Why is this? Presumably I am missing the binaural cues to segregate the sources (and the associated echoes?), but I still have the outer ear, head and body filtering that gives different sources different spectral characteristics (the so-called head-related transfer function or HRTF.) The speaker phone takes away all of these, while the stereo microphone retains the level and timing differences. Much work has been done on binaural recordings using artificial heads and torsos as well as in-ear microphones, but most of it has focused on veridical perception of location. Conversely, the work on masking mevel differences investigated the importance of binaural correlation to detection but did not include HRTFs and did not focus on speech. It might be interesting to combine these and measure speech intelligibility in noisy environments with and without appropriate HRTFs (which include interaural differences in time and level.) Erick Gallun Graduate Student, Hafter Auditory Perception Lab UC Berkeley

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