[ProAudio] stereo perception through headphones

Bill Whitlock engineer_bill at verizon.net
Thu Jan 30 10:48:58 EST 2020

Hello Group,
I'll just throw my 2-cents worth in here. Although electronic circuit design is my thing, I designed all the hardware for the Spatializer(R) that was popular in the 90s, both in mixdown (the "pro" unit) and in consumer electronics (via an IC made by Matsushita/Panasonic). The pro device allowed 2D joystick panning of individual channels in mix-down. The consumer IC expanded separation for devices with closely-spaced speakers. In the early phase of hardware design, I had hours of discussions with its inventor Steve Desper (former recording engineer for the Beach Boys), where I learned a lot about directional cues in human hearing (I'm by no means an expert, but I "get it" generally).  To grossly over-simplify:  Our ear/brain's most dominant directional cues come from IAD (inter-aural delay) due to the length of the acoustic path between our ears (roughly 1 milli-second). The direction of the sound source creates arrival time differences between the two ears - except the front-and-center case, where they're obviously equal.
In true binaural recording, mics are at ear position on a dummy human head, so the recording is of signals as they arrive at each ear of the dummy - therefore, the IAD becomes part of the recording.  In "normal" stereo recording, signals are recorded as they radiate from their sources in space around the listener - the IAD is provided by the listener's own head, and is NOT part of the recording. So when a normal recording is listened to with headphones, the IAD is missing - which confuses our ear/brain perception mechanisms and sounds very un-natural (usually grossly exaggerated separation and an "inside my head" perception) when listening to conventional "pan-pot" mixes.
IMHO, this is an apples vs oranges problem and any conversion between the two would, of necessity, be very complex!
If I recall correctly, back in the 1950s, a fellow named Bauer recognized this problem and developed some electronic "cross-talk" networks to process normal recordings to sound more natural in headphones.  As Scott said, various schemes have been tried over the years - with variable success.  I honestly don't know if any of the providers of headphone only products (which are all the rage today) have attempted to "fix" this problem. Or has the younger generation just accepted this "strange sound" as normal (as with MP3 and other highly processed audio). My biggest fear is that, as speaker reproduction loses popularity, recordings will be made specifically for headphone listening ... which would make them "weird" sounding over speakers. Perhaps this is a fear because I'm not a big fan of headphones, especially in public spaces - I use them only when listening to noise floors or evaluating distortion.
I hope this might shed a bit of light on the discussion. Now back to work!
Bill WhitlockWhitlock ConsultingAES Life Fellow - IEEE Life Senior Member642 College DriveVentura, CA  93003Office (805) 755-5018

-----Original Message-----
From: egosfield via ProAudio <proaudio at bach.pgm.com>
To: Proaudio Group <proaudio at bach.pgm.com>
Sent: Thu, Jan 30, 2020 8:57 am
Subject: [ProAudio] stereo perception through headphones

  Since the list has been quiet -- I hope this is not inappropriate:
 I am unable to perceive a virtual soundstage when monitoring stereo tracks through headphones.  I wonder how common this is.
 I use them for tracking, but not for mixing or aesthetic editing.
 I can form a subjective impression of the timbre of instruments, distance from  and characteristics of microphones, timbre of room reflections, sometimes the size of the room, depending on apparent reverb characteristics.
 But central signals always feel like they are in the center of my head, and the subjective image extends outward from my head like a figure of 8 microphone with lobes parallel to the soundstage - mickey mouse ears.  I have tried various HRTF modifications with no significant help.  I still perceive central images in the center of my head, and the virtual soundstage is never in front of me.
 I had assumed that this was my own neuro-cognitive 'deficiency', like people who are unable to free view stereo image pairs (which i do easily, wall eyed or cross eyed) or who can not in fact perceive visual stereoscopic information at all  and do not see stereoscopically (there is up to low double digit prevalence of this in the gen pop).
 But a good friend who is a well respected designer of high fidelity equipment has the same response.
 I have Stax, Etymotics, Sennheiser HD580, and AKG 240 'phones and  my 'soundstage' experience is the same through all of them.  Lots of detail, of variably contoured frequency response, but no 'real' soundstage.
 Yet i see headphones commonly evaluated for "sound stage" and people report hearing a virtual performance space in front of them.
 I am also unable to perceive effective binaural imaging -- central images remain in the center of my head, although more lateral content seems more peripheral, and  only the lateral virtual sources seem anywhere slightly forward of my head.
 I'm now old enough to have lost hearing above 14kHz, but i had the same headphone experience when  I was in my 20s and could hear television CRT synch tones. I have no problem with stereo localization with speaker playback, and can easily distinguish the type of spatial clues provided by coincident microphone techniques vs. those of near coincident (ORTF, NOS etc.) with time of flight differences included.  I remember (and saved) the long discussion here about coincident vs. near coincident techniques.  I prefer near-coincident aesthetically if there is any depth in the array of performers.
 I haven't found a good discussion of this kind of 'deficiency' in easily available neurological or audio sources.  I checked a few texts I own on audio perception (Berg "The Physics of Sound", Butler "The Musician's Guide to Perception and Cognition", McAdams ed. "Thinking in Sound - the cognitive psychology of human audition" but found no relevant discussion of headphone soundstage reproduction of stereo music (although Butler comes with a CD of examples utilizing headphone playback for examples of perceptual issues in tone localization).  The ENT literature I have access to is even less relevant.
 I'm trying to find out if my deficiency is relatively common, and other folks just report as headphone 'soundstage' a level of perception that I consider inadequate to deserve that description,
 Can someone point me to a discussion of such variability in stereo depth perception through headphones?  I suppose the people who create HRTFs have done a bunch of work on it. 
 I can also note that in the past, i had a "Professional" (HA!) Sony Walkman cassette deck that sounded reasonable through headphones, but when used as a line in to a good stereo system for speaker playback showed unacceptable and easily perceived flutter.  My ear/brain system was somehow canceling or ignoring the flutter  when listening through headphones.  
 If this is not appropriate to the list, the moderator can just delete it. 
 Considering how many people use earbuds for their music listening these days (and mp3 files).   I hope this issue has been address technically somewhere.
 best wishes to all,
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ProAudio at bach.pgm.com
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