I've been asked about the settings I'm using with Audirvana for the graphic equalizer, and since the main criticism regarding the BHA-1 seems to be related to the frequency response (and any harshness caused by it), I think this is very relevant to this thread (for example it means I'm seriously interested in it, and am setting up a demo at a local dealer).
Meanwhile I've spent many hours tuning the settings, there seems to be a mutual benefit from attempting to develop a set of settings which can be used for very different music. I'm using the audio unit called AUGraphicEQ (the Audirvana preferences window has a new tab called "AudioUnits"), it seems to be very good quality, and apparently does its computation on the (possibly up-sampled) 24-bit conversion of a 16-bit file. I've gotten to the point where these settings, to my ears, improve the subjective sound quality from "computer audio with a cheapish touch" to "sincere Hifi equipment".
They have somewhat similar benefits even when used on the internals speakers of the computer, so it doesn't seem to be my specific equipment or headphones (although you'd probably fine tune them for specific equipment). However, in order to avoid distortions (real ones) at high volumes, each setting seems to have to be 0 db or lower. As you can see from the curve in the image below (if it posts correctly), some of the settings are below -6 db, so this reduces the overall volume substantially. One will need a headphone amp with sufficient extra power, which the BHA-1 seems to have. I suppose this is the reason why music is sold in the current form. The settings below takes of few minutes of getting used to, but for me there is no way back. For example, voices sound much more they way I would expect them to sound. I wonder if hifi speaker set-ups make a similar "conversion" as a matter of the frequency response of the loud speakers (or in the CD player?).
(Click for larger version)
The most important part seems to be to reduce the range between 800 Hz and 2 kHz, while leaving the range around 3 kHz to 6 kHz quite high (as well as the bass region). I can definitely say that "wrong" settings can subjectively cause harshness and other apparent "distortions".
Keep in mind this combination of settings is still evolving and may have some faults I haven't discovered yet, even though I've tested it with a lot of different music, such as Keith Jarrett's Köln Concert, Bob Dylan's diverse voice(s), Pink Floyd, classical music (current favorite: Anne Akiko Meyers), and Klaus Schulze (with Lisa Gerrard)'s demanding sound variations.
Edited by soundscape1 - 6/13/13 at 11:14am