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by Herman Burstein Tape copying Q. In transcribing recorded tape and phono discs onto tape, would we be able to economize on tape by using an "extended range" tape at 3.75 ips without affecting quality? Or is 7.5 ips still the speed? To preserve the original quality of the recording over decades, would we do better with acetate base, 1.5-mil polyester, 1-mil polyester, or 1-mil tensilized polyester? For cleanest recorded sound, is it necessary to use a bulk eraser to erase a previously recorded tape? If so, what criteria should we use in shopping for one? Joe Horning, Kent, Ohio. A. (1) Whether you can copy at 3.75 ips without significant loss of quality depends on the quality of the tape machine, of the copying tape, and of the recorded tape or phono disc. The only thing I can venture is that there is a reasonably good chance of success, considering strides in the state of the art over the past few years. The wisest thing is for you to try copying first at 3.75 ips, then at 7.5 ips, and compare each copy with the original on an A-B basis (2) For preservation of tape quality over a long period of time, including minimum print-through (which increases with time), 1 1/2 mil polyester tape is generally preferred. (3) If a previously-recorded tape has been subjected to a high recording level, or if for some reason the previously-recorded tracks do not line up exactly with the recorded tracks of the machine you are now using, it is advisable to use a bulk eraser. I can't advise you on criteria for purchasing the eraser. I think that the price differences among erasers reflect convenience features and duty cycle (how long you can operate the eraser before you have to allow it to cool) more than quality of erasure. Echo chambers Q. I am ever fascinated by the different types of echo chambers used. Recently I spotted one that was rather long, wide, and narrow, made of beaverboard, I believe. I asked the engineer how it worked, and he said that one end houses a speaker, and the other a microphone. You just feed a signal through this device and voila!-echo! If this is true might I build such a unit at home? Do you know of any place that offers plans for such an echo device as I have described? Would it be possible to take one channel of a four track machine, feed it through such an echo device, and get a signal complete with echo on the other channel? Would there be any power supplies or electronic devices to build for use in conjunction with the above mentioned structure? If so, what? How would I control the extent of the echo? Any answers you may be able to provide concerning a home-made echo chamber would be greatly appreciated. A. I cannot claim expertise on acoustic echo chambers such as you describe, and cannot refer you to plans for such a device. It would seem you might try to copy the construction and dimensions of the one you saw. It appears that the type of echo device you describe would favor a certain range of frequencies, depending upon its dimensions. However, this is not necessarily detrimental to the effect you seek. As you say, it would be possible to play one channel of a tape machine (assuming this machine can play one track while recording another), feed the signal through an echo chamber, and record the result on another channel. This signal would have to go through a power amplifier in order to power the speaker of the echo chamber. I think that the amount of power required is quite modest, so that a simple power amplifier capable of putting out a few clean watts (perhaps as low as 3 watts) would be sufficient. You can purchase such a power amplifier for a relatively small amount from one of the kit manufacturers. To control the amount of echo, it would be necessary to combine the output of the echo chamber (the microphone output) with the signal originally fed into the chamber. In other words, the two signals would have to be combined in an electronic mixer. Accordingly, the playback channel of the tape machine would feed into two devices: (1) through a power amplifier into the echo chamber; (2) the electronic mixer. The microphone of the echo chamber would also feed into the mixer. The combined signals would go from the output of the mixer into the tape machine for recording on another channel. Depending on your tape machine, it could possibly be used as the mixer (that is, some tape machines permit mixing of low-level and high-level signals. (Audio magazine, Jan. 1968) Also see: = = = = |
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