On balanced DACs/amps and HRTFs...

So life was relatively easy, though full of too many headphones (first world problems, eh?) Then I got mildly frustrated by the XDuoo X3's need for a new battery, which I resolved, and the nearly-need for Rockbox (which was almost a great solution for me), and then the Onkyo DP-S1 Rubato was on sale and life was better. Fully balanced now was an option, hmm. Had always been a mild curiosity, so now I have the Fiio F5 (yay balanced cable included), a balanced cable for my Hifiman HE-400i, and after a bit of work one for my Onkyo ES-CTI300 (thanks Penon, no thanks Fiio and whoever came up with the MMCX 'standard'). Surprise! Balanced is different... I think better... maybe much better in some circumstances... but I will need to spend some time figuring that out. Didn't have an easy way to swap balanced to unbalanced with the MMCX connectors until I just recently got an adapter to go from 2.5mm TRRS to 3.5mm TRS. The Hifiman seems to benefit the most in my limited tests so far... and now I'm curious about getting something balanced to replace the SMSL SD-793II I've been happily using (TI DIR9001, PCM1793, OPA2134).

But if I'm going to do that, I want to understand everything better. Also, if I'm going to put serious money down, I'd like to figure out a good HRTF strategy. Have enjoyed Creative's EAX in PC games over the years (both through their legacy APIs and via their OpenAL extensions), Blue Ripple's work with Rapture3D, and most recently the Dolby Atmos headphone implementation in Overwatch, as well as more traditional binaural recordings from labels like Chesky Records as well as BT's experimentation with HRTFs in recent albums (especially _). In cases where EAX/Atmos Headphone is simulating elevation, I get some sense of it, but haven't yet experienced the precision I'd like, so I'm sure the HRTF tech has room to improve, but I appreciate an HRTF that's well matched to my head vs. no HRTF.

For a while I've been thinking that since modern DAPs and now some desktop DACs have so much extra horsepower it would be great if they had a built-in solution for selectively applying an HRTF to solve the fundamental headphone "in the head" issue due to the unnaturalness of headphone vs. live or speakers in a room listening, but from what I've gathered HRTFs seem to be either ignored or given short shrift compared to all other features. In the budget balanced DAC/amp space I only know of one product that includes an HRTF solution, the Monoprice Monolith Desktop Headphone Amplifier, and who knows how good that will be since it's not out yet (from what I've gathered Dirac Sensaround II should be ok, but more on why it probably won't be great shortly). Topping released their revised DX7s, no mention of anything HRTF, same with SMSL M9.

Meanwhile, I wanted to understand the technology of HRTFs, headphones, and their relationship to human hearing better. This has been the most interesting resource I've come across so far:

http://www.davidgriesinger.com

In particular, from 7/19/13:

There was interest at these meetings in my binaural recordings of concert halls, and in the methods I used to construct the small probe microphones. I updated the slides in the link below on binaural hearing and headphones to include more data on the construction of the microphones. "Binaural Hearing, Ear Canals, and Headphones" http://www.davidgriesinger.com/Binaural_hearing_and_headphones.ppt I also re-discovered the presentation I gave in Munich in May of 2009 on frequency adaptation. This presentation goes into the details of how the ear localizes sound in the vertical plane, and why this localization fails when timbre is not reproduced exactly. It explains why most headphone sound is perceived inside the head, and why binaural sound can be perceived correctly without head tracking if the recording and the playback is equalized at the eardrum. "Frequency response adaptation in binaural hearing" http://www.davidgriesinger.com/binaural_hearing.ppt​

And from 11/12/17:

At the ISEAT2017 conference in Shenzhen China November 4th and 5th of 2017 I presented a new version of the talk on concert halls and headphones, once again called "Laboratory reproduction of binaural concert hall measurements with individual headphone equalization at the eardrum." The slides contain translations in Chinese.

New in the slides is a summary some of the significant errors in previous work on headphones, hearing, and room acoustics. I believe thattThese errors have had led to serious mistakes in these fields. There is also a brief look at my current work on reproducing binaural recordings with crosstalk cancellation.

The crosstalk system is a refinement of a program we called "panorama" in the early CP1, 2, and 3 series of Lexicon processors. It works much better than before, and much better than I had any right to expect. A listener who has performed the headphone equalization process can put the headphones on and off while sitting in front of the speakers. The sound image and timbre are almost identical. The advantages of the crosstalk system is that it requires no individual equalization, and small rotations of the listener's head keep the front image stable, just as with normal hearing. If you are interested in trying this system, contact me by email. "Laboratory reproduction of binaural concert hall measurements through individual headphone equalization at the eardrum ISEAT2017" http://www.davidgriesinger.com/Accurate_reproduction_ISEAT2017.pptx​

From what I can tell the work his does is solid and I'm very impressed with what I'm reading, but I may not be the best person to judge since I am a bit out of my depth here. Anyone have any associated resources/reading I can do to better cross-check this information? There are a lot of generally fascinating implications for the work he's doing as it pertains to headphone design and our models and understanding of human hearing, sound localization and HRTFs. From slide 56 in his most recent presentation:

More Conclusions

• Current headphone technology ignores the enormous importance of individual ear canal resonances
• The result is incorrect timbre and in-head localization.
• Individual equalization at the eardrum to match a frontal source corrects both errors, allowing accurate reproduction of both conventional music and binaural recordings.
• Our equal loudness software can non-invasively make both measurements.

​

This gives me pause with regards to investing significantly in any HRTF solution since (such as Blue Ripple Rapture 3D Advanced, IRCAM Hear V3, HPEX, Out of Your Head Software, or Hajo's Headphone Enhancer). if he's right, it looks like there could be some significant improvements in the future with this technology. In the meantime, I was thinking of sticking with free software solutions in a desktop listening setup, such as Tom Ammermann's Spatial Sound Card, Razer Surround, or the upcoming VLC 3.0 with 3D Sound Labs HRTF technology.

What is everyone's favorite HRTF solution, and what do you all think of David Griesinger's work?

 

I've applied his method as explained on YouTube to all my headphones and got the best results I've ever heard in terms of frontality of virtual sources, and also the best FR I've ever heard on each pair I did this for. (Only other thing that gave me frontality for a few instruments in a few songs were 2-3 of the demo samples of the Out of Your Head software, other than that no crossfeed or "spatial" effect has ever produced true frontality for me.) As long as I can help it (as long as I can have a viable system-wide convolver DSP solution for my phone, like ViPER4Android is for now), I'm not going back to using headphones without a personalized "Griesinger equalization".