I have become a huge fan of cross-feed since I got my Meier-Audio StageDAC. To be honest this is the only implementation of cross-feed I have heard but it is extremely good indeed and imho represents a great improvement in the quality of the signal, in fact I think it produces a very much more accurate rendition.
I had been very skeptical of the idea because I am old enough to remember "mono reprocessed for stereo" (ugh!) and of course I have the idea that surely processing the sound cannot be good.
However the big problem with headphones is that by design they greatly disturb the stereo image created by the recording engineer/producer.
Listening to classical music comparing with Meier-Audio cross-feed on and off is very interesting and reveals that the Meier-Audio cross-feed really does great work in correcting the problem inherent in headphone replay of music originally intended for stereo loudspeakers.
There is a fairly standard "layout" for an orchestra, they are in front and the sound for loudspeakers is usually mixed so that the listener has an ideal position which is a bit back from the position of the conductor. This position is not available in the concert hall but it can, and is, made available in the recordings.
With headphones, however, this arrangement goes monstrously wrong. Musicians playing on the left or right of the orchestra end up playing as if they are right beside you on either side. The detail on their instruments becomes very misplaced and greatly emphasised over the rest of the orchestra.
I have one recording which reveals to me just how wrong things are with headphone replay (without cross-feed) and that is Poème Symphonique for 100 Metronomes by György Ligeti. The performance I have is by Françoise Terrioux in 1962. "100 Metronomes" is excatly what you get for 19 mins 56 secs. The metronomes are placed in front of the listener and tick away very nicely. They should create this rather marvellous sonic sea of ticking. If I use headphones without cross-feed then there is, what sounds like, a great deal of surface noise and static as you would expect from a worn LP playing a historic recording. Turn on the cross-feed and this goes away and you can hear that the metronomes are in front of you and ticking away nicely. I think this "surface noise" from headphones without cross-feed is simply out of place detail from the metronomes at the right and left sides of the metronome array. This piece of music in its defined sonic structure is very illuminating for this fault with headphones.
Listening to more conventional classical music I find that the cross-feed restores a great sense of integrity, particularly to music from the actual classical and late classical/early romantic periods.
Some people complain that cross-feed loses a sense of air, but if you think about it there really shouldn't be a sense of air around the listener for classical music recordings. There are many microphones on the orchestra, but there is no microphone to record an atmosphere for the actual location of the listener. The sense of air that comes from using headphones without cross-feed is in fact the atmosphere from the microphones at the extreme right and left of the orchestra which is wrong placed right next to the right and left ears of the headphone wearing listener. As soon as you turn on the cross-feed, then that wrongly placed sense of air returns to the correct position.
When I bought my Meier-Audio StageDAC I thought that it was a nice "extra" to have cross-feed, but I now find that I always use cross-feed and for me it always improves the listening.
