inna,
Here is my quote: "We should also consider some master dubs at 7.5 ips I have heard some of these and I must say in most instances that I absolutely cannot tell the difference between a 15ips half track and it's 7.5ips half track copy."
Easy to explain. Note that I said we should consider 'some' and in 'most' instances.
If you are making a half track master copy from 15ips to a second generation master half track at 7.5ips, and your machine is properly calibrated you really won't hear a difference on most material. Look at a machines spec at 7.5ips and compare it to the spec at 15ips. I personally can't think of even one machine that specs better at 15 than it does at 7.5ips
15ips became the defecto setting in the 1950's, because it allowed high end frequency extremes. As machines electronics, more importantly head design improved along with the quality of tape, 7.5ips half track can easily match the performance of most material recorded at 15ips.
The other reason that material is recorded at 15ips and 30ips in the studio is headroom. Here, when recording live these speeds have an advantage. This however does not translate into making a dub. The dynamics of recording a drum set live is completely different that dubbing a recording of a drum set.
At the slower speed, nearly every machine will give you more bottom end, and all of them will easily spec to 20,000hz +/- 1db.
The source material matters as well. If you are listening to classic rock, and the machine is running at spec, you won't hear a difference. This is also true of complex classical. With solo instruments, piano and guitar it's much more difficult because of the frequency limits of the solo instrument itself. Your not going to hear a 35hz note from a Martin D-45 for example.
If we are talking about quarter track, then there is not contest whatsoever. But with half track, 7.5ips the sonics can be outstanding.
I have several half track 7.5ips second generation studio master that will make your jaw drop.
And my point was not to create a debate as to tape speeds, but to provide an option for those wanting to purchase prerecorded tapes at a more reasonable cost. And keep in mind that, and a second generation half track master at 7.5ips will blow the pants off of its vinyl brother every time.
Norman
