> 7. Reel to Reel Tape, Speeds and Software Equalisation > (Steve Fosdick) Hi, Steve, > I can record the output of the tape machine running at 7 1/2 inch/sec and > then use software re-sampling (sox, or sndfile-resample) to get a file > that plays at the correct speed but I wonder if I should also be applying > some equalisation in software as multi-speed machines usually have > different equalisation constants for different speeds. The idea thing would be to record it at 88.1kHz, then you'd only have to decimate it (i.e., downsample by 2, with no filtering) to get the result you're after. Reconstruction filters on playback would be giving you free anti-aliasing. :) This would also have some (really mild) noise reduction benefits. > So, does the equalisation compensate for the record process or playback > process at a given speed or a combination of both. If it compensating > only for playback then I should be OK, otherwise I presumably should be > applying extra EQ in software - anyone know how I could calculate what, > assuming I have the usual LADSPA plugins at my disposal and that the > signal has already been through the playback EQ for 7 1/2 inch/sec? You probably don't need to get very uptight. I think what you're referring to are the NAB/IEC/DIN EQ curves, but I don't believe those were ever specified for the speeds you're talking about. If you were worried about the response for 15ips or 30ips, then sure, it would make sense. But the odds are that the EQ circuits at your disposal are fairly funky to begin with, so I'd really recommend doing it by ear. (It always chafed a little, but even doing pro level mastering, that's what it comes down to for a lot of tape decks.) In fact, unless you were given a set of calibration tones for the partcular machine that *made* the recordings, you really have no other choice. This is a really long way of saying, "Yes, EQ compensates for _both_ record and playback." HTH. Phil M P.S.: If these are mono recordings, you will get about 6dB of noise reduction by summing the two channels of a stereo playback machine to mono! -- Dept. of Mathematics, 342 Machray Hall U. of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 Office: 446 Machray Hall, 204-474-6470 http://www.rephil.org/ phil at rephil dot org
