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Study the Vocal Splicer Application Hints for more details!
Switch TipIf you have an analogue console, it is good practice to exercise the switches the signal passes through. At least once a month, toggle every switch on the console. More often if you have smokers in the room. If the desk has been sitting for a while and you have a big session coming, it is a good idea to toggle all the switches before the session. This removes the oxide from the contacts and helps to keep them clean. Doing it before the big session will help prevent an intermittent connection from an oxidized switch, in the middle of the perfect take.
Demagnetizing Heads and Tape
Digital Machines - NEVER DO IT!!!
Heads stacks on digital machines are not designed to be demagnetized. I don't know the technical reasons why, but if you do it, make sure you have about $15,000 to spare to replace the head stack. (No, I never did it)
Analog Tape Machines
Ideally the heads could be demagnetized for every pass, but of course that is impractical. Daily should suffice. The trick is how to do it. Turn ON the tape machine. Yes, ON. Put the machine in INPUT. No harm will come if you don't set input, but the meters and possibly your monitors may object. The reason for input is when power is applied, the power supplies may not come up symmetrically and there is the possibility of a DC current pulse passing through the head. DC and iron make permanent magnets. Magnets erase tape.
The reason no harm comes to the tape machine is that all that happens is the head amplifiers clip. As these are inherently low current amplifiers, there is no danger to the devices in the amplifiers. I have done this on almost all multitrack tape decks made in the last 20 years. The same technique works for cassette decks and open reel recorders.
To actually demagnetize the heads, plug the demagger in at least four feet away from the heads and bring it up slowly to the heads. Move it slowly over the heads and guides, taking care near the heads. Now slowly move it away from the heads and unplug it when it is about four feet away. DO NOT use a demagger with a switch because if the switch is released or fails near the heads, you could have a set of magnetized heads that will be difficult to demag without a much more powerful demagnetizer. They are magnetized by the collapsing field, which could be quite intense depending where in the AC cycle the power stopped. For the really paranoid, you could use a computer UPS to power the demagger, to insure clean, uninterrupted power just in case the power failed while demagging.
One of the myths is how easy it is to demagnetize tape. Tape is very resistant to demagnetizing. Once for my own education, I took a tape and played it, while moving a demagnetizer up to the tape. While this was very uncontrolled and unscientific test, I could detect no appreciable difference until the demagnetizer was within a couple of inches of the tape. There is no need to remove tapes from the control room when demagging, as I have seen done. If tape was that easy to erase, the fields from all the transformers in all the gear in the control room would wipe the tape as you walked in.
If bulk erasing tape, don't just set the tape on the bulk eraser and turn it on, erase the tape and turn it off. If you do this, you will leave a pattern on the tape which can be heard if played. As the erase head does not erase all the tape, but leaves a small gap between the tracks, this noise could possibly remain and form an undesired part of the recording. The correct way is to turn on the bulk eraser, bring the tape up to it, erase and slowly move the reel away. If doing tape wider than 1/4", turn the tape over and repeat. Doing both sides gives an even field all across the tape and a more consistent background noise.
Just to be on the safe side, set your wallet with credit cards down a few feet away from where you will be demagging.
Tech Tip - Monitor S/N Ratio
Many people insist on running the monitor loudspeaker power amps at full level and only using a portion of the output available from the console, i.e. the control room monitor pot never gets past 12pm, even when listening on STUN. While it is true that some power amps in the past used to suffer from input coloration when the input attenuators were turned down, good modern amps usually do not suffer from this problem. Set the input level on the power amp to give a level slightly louder than you would ever listen when the control room monitor pot is fully up on the console and you will achieve maximum signal to noise ratio for the control room monitors. All desks exhibit some noise. Adding 40db or more typical power amp gain to the noise and attenuating the console output needlessly, results in less than optimum signal to noise ratio heard on the monitor loudspeakers. The residual console noise is perceived as a masking signal which degrades the transparency of the perceived mix. The mixer often adds more eq or compression than necessary to get the mix to jump out of the muck.
Consequently on a playback system without the masking noise, the mix sounds overly processed and unpleasant to hear. The same principle applies to Cue systems.
For those of you running a mixture of Pro (+4) and Consumer (-10) equipment like CD and cassette players, the best solution is to bring this external equipment up to +4 level before connection to the desk. Several manufacturers make such devices and they are fairly inexpensive. Those of you handy with soldering irons can make an eight channel device to handle four external players for less than $50. It's well worth the effort.
One Bit DACs and Music
Several CD players today 'feature' 1 bit DACs and oversampling. This is done because a 1 bit DAC has no non linearity's, as do all multi bit DACs. The output of a 1 bit DAC is either 1 or 0 and as such can have no error. These DACs are cheaper to produce. The machines employing them convert the data read from the disk to an oversampled data rate of 64, 128 or other multiple of the 44.1KHz CD sample frequency.
To output the changes between samples, the number of 1's and 0's is altered to give the desired input to the output filters. For example for a 64 times system, if the level did not change between two 44.1 samples, there would be 32 1's and 32 0's in the output stream. If the level goes up, more 1's are output and less 0's. If the level goes down, more 0's and less 1's. A 16 bit system, as CDs are, have a possible 65365 steps from top to bottom. From inspection, it can be seen that with 64 times oversampling, at most 64 steps can be output during one 44.1 sample. If a very steep transient occurs, it is impossible for the 1 bit DAC to output enough energy to faithfully reproduce the transient, and it is distorted. Most of the time this is not a problem, because there is very little energy in the higher frequencies of music. However, it is distorted none the less.
So, what to buy. An 18 or 20 bit Oversampled system would be free of this problem, and all other things being equal, should reproduce the music more faithfully. The extra bits on the 18 or 20 bit DACs reduce the error inherent in multi bit DACs and are discarded to help reduce distortion. The oversampling means the output filters can be more gentle and should result in more faithful reproduction. Just be sure to listen to your favorite kinds of music on several machines before plunking down your cash.
The Early Machine
When recording, often it would be most useful to have an "early machine." Now you may ask what is an early machine. We all know what a delay line is and have used them in creating interesting effects. Well, an early machine is just the opposite of a delay line, it makes things happen before the actually have.
An early machine is most useful to trigger synths or drum machines ahead of when the signal on tape occurs. By triggering the devices early, the delay inherent in the processing of the device is removed and the track keeps a much better feel. The output of the early machine is fed into a delay line. The output of the delay line is fed into the trigger input of the device and the delay is adjusted to align the new signal with the one on tape. Or even make it earlier if the one on tape is too laid back.
An early machine can also be used to move a good, but rushed (early) vocal performance into time. The output of the early machine is fed into a delay line and the delay is adjusted until the vocal is in time with the track. This is much easier than sampling and then trying to fly the sample in by triggering the sampler.
An early machine can also be used to align video to audio playback. Every so often, one gets a video tape with the SMPTE out of sync with the picture. Simply place the early machine on the timecode track of the tape deck, feed the SMPTE to a delay line, the output of the delay line to the synchronizer and adjust the delay line until the picture aligns with the audio.
Once you have an early machine, it is a simple matter to move it into the track slot of the card cage for the required track. Unless you are certain that your tape machine can handle this with the power on, TURN OFF the power. Be sure to mute the control room monitors and any cues, regardless.
To build an early machine, you need a three head analog tape recorder, a set of schematics for it, some wire, an hour and the connector of your choice. Optionally, you can make the early machine on a spare card for the recorder and/or add an output buffer if you have to drive the signal a long way or the playback amplifier is not capable of driving the new load. The ubiquitous 5534/32 can handle this job with aplomb.
A three head tape recorder uses one head for erasing, one for recording and one for playback. When overdubbing, the record head is used for both playback and recording, leaving the playback head unused. Internal switches in the machine connect the output from either the record (SYNC) or playback (REPRO) head to the output electronics. The typical spacing from the record to playback head is 1-1.5 inches (2.5-4cm), and at 30ips, this gives an early signal in the range of 30 to 50ms. At 15ips, these times are double, but one rarely needs anywhere near this much time. Typically, less than 10ms are required to align, so typical delay settings range from 20 to 40ms at 30ips. It is not necessary to know the distance, just adjust the delay line until the new signal aligns to the desired point.
On the schematic find the output of the playback amplifier. This is NOT the output amplifier. Prior to any switches and post any DC blocking capacitor, add a 50ohm resistor in series with the output. Connect the +phase wire to the free end of the resistor and the -phase to a suitable 0v connection close to the output amplifier. A good connection point is across the pull down resistor on the DC blocking cap. Wire the other end to your connector and voila, an early machine. If you have to drive the signal more than 30 feet (10m) or so, it may be advisable to add another buffer or balancing amplifier so as to not load the output of the playback amplifier. As long as the input of the device you are driving is a high impedance, everything should be all right. You can check this by placing the tape deck in playback and monitoring the channel with the early machine. Connect and disconnect the delay device and listen for any degradation to the original signal coming off tape.
WARNING: Over use of the early machine can lead to a severe case of DEJA VU!
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