On Mon, 8 May 2006 19:28:35 +0100 Steve Fosdick <lists@xxxxxxxxxxxxxxxxxxxxx> wrote: > A friend of mine has some old reel-to-reel tapes which we'd like to transfer to CD. Unfortunately most of the material was recorded at 3 3/4 inch/sec or 1 7/8 inch/sec and the only speed my reel to reel machine will do reliably is 7 1/2 inch/sec. > > 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. > > 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? > > TiA, > Steve. Wow! That's a biggie :( >From (not perfect) memory. Recording Eq is mostly Treble pre-emphisis and some Bass boost, to compensate both for recording losses and to provide a recorded (on tape) response that is substantially flat up to about 5kHz, then rises till about 15kHz then levels off again. The first complication is that, surprisingly, the faster the tape speed the more Bass boost is required. Not so surprisingly, the faster the tape speed, the less pre-emphisis is used, but this is not a linear relationship. Doubling the tape speed does NOT double the turnover frequencies that are used. On playback any remaining Bass lift is supposed to be removed partly by the failing LF response of the playback head (which will again be different at different tape speeds and partly by filtering which is also intended to reduce LF noise. At the HF end a lot of tricks are used, especially at the lower tape speeds to get just that last bit of 'top-end'. It's all there on tape but the head gap size is critical. By playing back at the 'wrong' speed you mess up all the clever balancing acts and, especially for recordings made at 1..7/8 you are likely to have all sorts of dips and peaks. Top end was never especially good at this speed but you will make it even worse. Consider, a 10kHz recorded signal will now be coming back at 40kHz, and unless you have an exceptional machine, it probably won't be coming back at all. I suggest that the best you can do is see if you can find a vynl or CD copy of just one of the tracks and use this as a reference to set up a graphic equaliser to get somewhere near the right sound for all the tracks. Better of course would be to find some kind soul with a multispeed tapedeck! -- F
