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Inter-Aural Time Delay

Discussion in 'Sound Science' started by Skycyclepilot, Oct 13, 2018.
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  1. Skycyclepilot
    I'm wondering if anyone else has experienced this... Until a couple of years ago, I could not listen to music with headphones because the image was always centered far to the left. It was not a balance issue caused by a loss of hearing in one ear. Any attempt to center the sound stage with a balance control totally "blurred" the image, making everything sound even worse. The problem even existed on speakers, but not nearly so badly that I couldn't enjoy music on speakers.

    Then I discovered Equalizer APO for Windows (free). Assuming I had hearing loss at only certain frequencies, I spent months tinkering with E-APO, trying to center the image that way. To a degree, it worked - and I obtained my first set of real headphones - HiFiMan HE400i. But things still didn't sound quite right. I kept experimenting...

    Quite by accident, using E-APO, I applied a tiny time delay to the left channel one day - and my blood ran cold, and a chill went up my spine. Suddenly the lead vocalist in a recording I was listening to jumped far to the right. I fined tuned the delay and managed to bring the vocalist to dead center with no other balance or equalization changes. For the first time in decades, I had a very good sound stage laid out before me with instruments about where they should be. I'm a classical pianist, have played music professionally, and have even dabbled in composition and song writing. Music is a really important part of my life, and suddenly, I was hearing it as if for the first time.

    In my case, the delay required was on the order of 120 µS - not milliseconds, but microseconds (.012 mS). I may never know why this works, but I suspect it has something to do with the way my brain processes sound. Perhaps it processes sound from my left ear just a tiny bit faster than from my right ear???

    I've heard others complain that lead instruments and vocals always seem to be left of center for them. If you've noticed this, you might consider experimenting with E-APO. Rather than use the program's delay, I use the free ITDPanner VST, which APO supports. Without it, I still would not be able to listen on headphones. I also have the Neutron Music Player for my phone, which has the ability to delay a channel by micro-seconds...

    I wonder if I'm just weirder than everyone else on this planet, or if anyone else has experienced anything like this. Caution - this discovery has turned me into a headphone nut, and cost me a lot of money...
  2. castleofargh Contributor
    the delay you picked would affect the position by a few degrees(modulo the size of your head), I personally can hardly notice such a change and need to turn the delay ON and off a few times to really confirm a difference. so I'd be tempted to say that you're making a pretty big deal of something rather small. not a problem or a critic as we all have one of those small stuff we're obsessed about that ends up really ruining our experience because we can't forget about it. but I thought I'd mention it for readers who might be thinking this is the new revolution in audio that will make it all so much better. it most likely won't.

    you're not telling about what you tried to determine the cause of your off centered feeling. like maybe:
    - put the headphone backward on your head to check if the shift is still in the same direction. if it is then it's you and not the gears or the tracks. and so whatever solution is for your own body.
    - try using mono to really have a clear target as to what should be the center.

    for example, I often get that feeling of music slightly off center, but that's because it often is on the album, or because my headphone has some FR imbalance. when I play a mono signal, I happen to get music well centered. and with a sine sweep on a pair or IEM with some significant imbalance at some frequencies, I can feel the position shifting when reaching those freqs, and then coming back to center. with some more testing using gears measured to be well balanced at various frequencies, I have a slight shift in hearing loss around 6 and 7khz where one ear starts to drop about 0.5khz before the other one and comes back up also about 0.5khz before(no idea what caused this).

    in my experience audio gears don't show big shifts in phase between channels, so I'd be tempted to expect what you're describing to be something caused by your own head/posture/habits. as for guessing a cause, I doubt that your brain processing both sides at different speed is the answer. in fact I doubt it very much. instead I'd be guessing that maybe you simple have one ear further back, or simply that when you're looking in front of you, your default resting posture has your head tilted a little. and when you use a headphone, you're now missing that usual delay so you feel like you're getting the opposite delay? I have no idea but my guess would be something along those lines if indeed your gears have nothing to do with the imbalance in time or frequency response.

    another guess would be specifically linked to using different left and right EQ with the wrong type of filter, resulting in an effectively different delay between channels. but your situation clearly goes well beyond that ultra specific use of EQ.
  3. Skycyclepilot
    You're going to have a hard time believing me, but I've dealt with this for forty years now, and have studied it every way you can imagine. I first noticed it when I put together my first real audiophile sound system with large, electrostatic speakers. I even went so far as to have my hearing tested, and there was no appreciable difference between my right and left ears. The problem has persisted for forty years, and with dozens, if not hundreds of pieces of audio gear. I am aware that not all recordings are perfect, and I do switch to mono when testing or centering the image. And I've put headphones on backwards, just to check, hundreds of times over the decades. The phenomenon is 100% consistent for me. I'm not imagining it.

    And for me, it is not a small difference. If I happen to turn the delay off and forget it's off, the instant I put my headphones on I notice it. Everything is centered a good 30° left, if not more. It is very distracting.

    By the way, the slight shift you are hearing at frequencies above about 6 KHz is probably not hearing loss. It's caused by ear canal resonances. Go to this webpage - http://www.szynalski.com/tone-generator/ - and with headphones, run the slider up and down from 6 KHz and up, and you'll hear the tone jump all over the place as various resonances kick in and out. This is a well known phenomenon. Some people even try to use notch filters to correct it. I've tried that, and could not hear the difference when listening to music, so I don't try to correct for it.

    When you said, "or simply that when you're looking in front of you, your default resting posture has your head tilted a little. and when you use a headphone, you're now missing that usual delay so you feel like you're getting the opposite delay?", you might have just nailed the problem. I have severe nystagmus. When I turn my head left or right, my eyes jitter badly. Interestingly, the jitter is minimized when I turn my head a little to the left - not straight ahead. People watching me drive have commented that I don't face straight ahead, numerous times. So, my natural forward-looking head position is with my head turned several degrees to the left. It is entirely possible that my head always being turned a bit left of center has trained my brain to accept sound reaching my left ear a few microseconds later as normal.

    Sound travels about 1.5 inches in the 120 µS I use as a delay to correct imaging when I use headphones. Perhaps the amount I tend to turn my head to the left puts my left ear about 1.5 inches further back than my right... Wouldn't it be amazing if my vision has actually created this problem.
  4. 71 dB
    If the ITD in seconds is know, the corresponding angle(ITD) in degrees can be estimated with approximate equation:

    angle(ITD) = 180° * (1 - SQRT(1 - 1184 * ITD)).

    So, angle(0.00012) = 180° * (1 - SQRT(1 - 1184 * 0.00012)) = 13°
  5. Skycyclepilot
    I would assume that that would be from a forward facing bisector line, straight out from the center point, directly between the eardrums... Here's what I do know - when I turn off the delay, the illusion is that the center moves to a point at least halfway between the center line and the left ear. I'm very much a person of math and science, and I can't explain it, but it is what it is.
  6. castleofargh Contributor
    the size of the head changes a little from people to people so that impacts the angle where we get such delay. but the general idea is the same.
  7. Prosny
    Hey, I've just come across this thread and I wanted to share my experience with you, since I too have a problem with voices shifted to the side (left, in my case).

    Like you, I've tried changing the frequency response differently on the two channels to try and centre all the frequencies, with the aid of a tone generator. The center I hear shifts many times during the sweep, almost certainly because of the different shape of my inner and outer ears (like everyone out there, I suppose). But yeah, that wasn't very effective, and I always found myself overcompensating leaving me with the voices kinda centered but with all the pressure on the right ear.

    One day, though, I've noticed that while listening to speakers I wasn't experiencing this phenomenon. That's when I came to know of the existence of crossfeed: I bet you know what it is, since you have a lot more years of experience than me. First I've tried the very, VERY bad implementation of Meier's crossfeed in Peace GUI for EQAPO (if you select it in peace and then open eqapo, you can clearly see what it does to the frequency response (spoiler: nothing good)), but even with that one I could clearly notice that everything had gone to its place without skewing other components. So after a while I settled on Case's Meier Crossfeed Component (you can find the thread on another forum), which is a VST plug-in you can use in EQAPO.

    I honestly don't know why the crossfeed fixes my problem, but my thought is that since wearing headphones my left ear only hears the left channel (and same for the right ear), my brain doesn't have the spatial cues it's used to, so it kinda messes with positioning on the soundstage.

    Right now I've settled for a "strength" of 0.15 on the vst plug in. It doesn't really put everything in balance like the super strong crossfeed on peace did, but it sure is a step in the right direction, and it doesn't mess too much with the frequency response. But, you know what? I'm also curious to try your delay method; maybe that's the lasts piece I miss to have the perfect image I have on speakers Thank you for that.

    P.s. If you need help with the vst plug in you can write here, since the 64bit version is kinda bugged and it needs a small command to work properly (all the information you need is on the thread on the other forum, though, it just took me a while)

    Hope my intervention was helpful to you. I wish everyone a good day
    Last edited: Oct 15, 2018
  8. Skycyclepilot
    Thanks for sharing. It does sound like you've been down the exact same road as I. I could have written your first paragraph, word for word! I am familiar with crossfeed, and I'm using the exact same VST as you, along with Equalizer APO. It's the one that crashes E-APO is you try to open it, so you have to enter the crossfeed value via text, within E-APO. I also found a strength of 0.15 to be about right. I use it mostly on pop/rock stuff with deliberately hard-panned recordings. Unfortunately, it does nothing to bring the image to center for me. By the way, Jonas is working on a new version of E-APO that might fix the problem with that particular VST.

    The Inter-Aural panning VST I use is on this page...


    You can use the Shift key and mouse wheel to find tune the delay, using the center knob. It works really well.

    Here's the 64 bit version of the Bauer crossfeed VST - thought you might want to experiment...


    It works perfectly in E-APO.

    Again, thanks for your post. I'm glad to know I'm not the only person in the world who has experienced this phenomena, and I hope the information helps others enjoy using headphones more.
    Last edited: Oct 15, 2018
    Prosny likes this.
  9. Prosny
    Thanks for the plug-ins, I'm gonna try them both.

    By the way, I had lost the part where you had written that you tried to compensate for the ear canal resonances but didn't hear a difference on music. I actually did hear a big difference: for the worse. Simple logic makes me believe that I shouldn't mess with those, since that's the way I hear sounds everyday. I only correct for the headphone's flaws, otherwise everything sounds dull and very unnatural (example: I have a very strong resonance at 7khz. If I tame it to about the same level of the other frequencies, and trust me it takes a lot of DBs, I lose every kind of "s" sound and everything sounds muted. Very irritating if you ask me). So in the end you're right not to mess with those, and that's why equalizing "by ear" is never a good thing, even though I read that as a suggestion every once in a while.
  10. Skycyclepilot
    I'll be interested in hearing what you have to say after you give the plugins a try.
    Prosny likes this.
  11. Prosny
    Holy s**t.

    Didn't even try the plugin yet. Just added delay to the left channel. 40us did it for me. I will adjust it with time, and I'm curious to see if it will solve another problem of mine, probably derived from all of this: whenever I use headphones I constatly feel like I'm wearing them slightly shifted forward on the left ear, while in fact they are not. It is probably because of the shifted image, which is quite a bit forward on the left side. Later in the day I will try the plugins (also to compare Bauer's crossfeed with Meier's), but for now I'm happy. Thanks, THANKS really for sharing this with us.

    Oh, almost forgot. The perceived sound quality is also much better, since now everything's well distributed and it's not all cluttered on one side. That's the best part, honestly. But, knowing myself, I know it's going to be a long journey until I find the right delay.
    Last edited: Oct 15, 2018
  12. Skycyclepilot
    You're welcome. I figured there were others that might benefit from the dozens of hours I've spent on this. If it helps just one person, it was all worth it, and obviously, it has done that... I've found that I have to adjust the delay slightly, based on what I'm listening to, how tired I am, etc. Admittedly, that part may be just in my head - it's easy to go down the rabbit hole on this. The easiest way to make sure you've got things centered is to listen to your content is mono for a bit. And the easiest way to do that is to use the Copy Channel command in Equalizer APO. Make it the first command in your configuration, and set it up like this...

    Copy: L=.5*L+.5*R R=.5*L+.5*R

    That way, you can easily switch between mono and stereo.

    The Bauer crossfeed works perfectly in E-APO, and it's adjustable. It has four presets, including Meier. According to the analysis panel in E-EPO, it does shave a decibel or two off the high end, though. I think that might be normal, which makes me wonder if Case's crossfeed is truly a crossfeed, or is just mixing a little left with right and vice versa...
    Prosny likes this.
  13. Prosny
    Thanks for the mono preset, until now I used a mono youtube video, but this way is much more convenient.

    Just tried the two plugins: ITDpanner works a charm, it's just a shame that the settings are on those obnoxious pots instead of having actual numbers to rely on.

    I didn't like the standard preset of the crossfeed plugin, but the Meier isn't bad at all. What's more it actually increases CPU usage by 4%, while Case's one only does by .1%. That might say something, but I liked the other one too, so I don't really know.

    What I know, though, is that this is the best thread I've ever read on Headfi. Thanks again. I came here trying to help someone and got helped instead ahahahaha.
    Last edited: Oct 15, 2018
  14. Skycyclepilot
    Wow, considering that most of my posts get ignored, that's quite the compliment. Many thanks for that. And you're welcome. I enjoy discussing this stuff, but rarely find anyone interested.

    Want an ITD VST where you can enter numbers? Here you go...


    You can change the numbers in this one by clicking the text button in E-APO, just like you do for Case's crossfeed.

    And your mention of CPU usage makes me even more suspicious of the Case crossfeed. I really wonder if it just mixes the channels a bit, without all the filtering and time delays a real crossfeed is supposed to do.

    if you prefer the Bauer crossfeed, using the Meier preset, you can compensate for that 1 decibel loss about 650 Hz by introducing a high shelf parametric filter in E-APO, set as follows...

    Corner Frequency, 550 Hz, - Gain, 1.05 dB - Slope 7.5 dB/Octave
    Prosny likes this.
  15. Prosny
    Psypan is awesome. I wanted finer control, I got it :beerchug:; there are at least 8 digits after the point. The high shelf works perfectly, I would have stayed with the -1Db without a problem, but since we can fix it, why not?

    Thanks again, I wish you all the best and some really good listening sessions.
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