I recently got my RS1500 back from servicing and biasing for RMGI 911. You can see the report on the results of the servicing in the Service Resources forum. A little back ground on how I evaluated the tapes.
As a source, I used my Apple powerbook with some home brewed recording I made which are uncompressed and which I've very familiar. Also, I used the cut "Yesterdays" from Patricia Barber's Night Club. These were sent through an M audio Audiophile 24/96 usb and were played in Apple lossless codec. The playback was through my modded Seduction with Amperex green label 7308's with a Silver Audio Silver Breeze tonearm cable and a Tom Evans Groove Tube ic. The amp used was an Eddie Current tube headphone amp and assorted headphones were used for listening.
First off, both tapes were recorded 1/2 track @ 15ips.
Both the 911 and 456 lost a bit of "air" over the source. This was pretty subtle, but if you listen for it, it is there. I could barely hear this on most of my headphones except for my Beyer dt880's. These are ruthlessly revealing of anything in the upper mid>highs as they have a tipped up treble.
Quantagy; There were 2 problems with this tape that alone, makes the 911 a no brainer. The main problem is in QC. I bought a few reels of 456 before the time before last, tape production stop. There was plenty of 456 left from many venders and I got this from my local Guitar Center. The problem is several low level drop outs. I doubt that you'd really notice these unless you were listening with headphones but I double checked a couple of the reels which had never been opened and they were all affected to one degree or another. During this evaluation, I switched tapes back and forth over 20 times and cleaned the heads twice.
The other problem that I had with the 456 could have been bias related and again, it is pretty subtle. On Yesterdays, the middle section has an extended instrumental section that features a lot of nice drums and bass. And when things got pretty intense, the 456 had a tendency to get a little fuzzy sounding with the instrument separation blurred. This is a wort that I have a real problem with. It's one of the reasons that I like tape for large classical pieces over my vinyl rig that is Oh so nice for smaller groups.
Another advantage that the 911 has over the 456 is headroom. I recorded the same Patricia Barber selection 4 times on each tape. Each time I increased the recording level (by half a number) for a real world analysis of the dynamic range of each tape. I was able to record a half number higher with the 911 for the same amount of overloading.
I also gave each a test of re-recording on the same bit of tape. Both did very well with 1 loud selection, then one soft, and repeat. So after recording the same section of tape 4 times, I didn't notice any obvious differences on the last play.
I listened with a pair of Audio Technica AD2000 headphones which have a nice extended bottom end. I think that the 911 had the edge on this as well. Both tapes were equal in extension, but the 911 had more texture and detail. When the electric bass hits just the right note and the bass cabinet creaks, you can hear it on both tapes but you can tell exactly what it is with the 911.
The last thing I tried was on the 911 only. I made this test with the idea of seeing if the 911 was a good replacement for 456 and if it was worth re-biasing and using as a real world everyday tape. So,.. I thought I'd give it a torture test and rewound and ff'ed a section I'd recorded over and over again. Stopping>starting, everything I could do to stretch the tape, till I got bored doing it. When I replayed the section, I couldn't hear any speed related artifacts.
Well, I think the 911 is a no brainer as Doc would say. Maybe if we can get enough of us to order some, we might be able to get a group buy discount.
