There are several different kinds of synchronization between different kinds of music and recording equipment. Here is a description of each, and its capabilities:
Proprietary synchronization systems
These systems usually work on only one manufacturer's equipment. An example is the system TASCAM had, using the "accessory port 2" on many of their older recorders. Depending on the equipment, it can synchronize music, and in some cases, fast wind positioning. Some digital systems can achieve sample-to-sample locking, being the most accurate synchronization system known.
GenLock
This does not keep the creative works in sync. What this does is make sure that every TV camera in use in the studio is in exactly the same place in the scanned raster at the same time. Without it, TV pictures would flip every time a different camera was selected by the console operator.
SMPTE Time Code
The Society of Motion Picture and Television Engineers (SMPTE) developed this time code to synchronize cameras filming the same event. The code contains hour, minute, second, and frame information, and can be recorded on an audio track. Unfortunately, there are four different "flavors" of SMPTE time code, and the same kind must be used for all cameras in a system. The flavors are:
SMPTE Time Code can be used to synchronize multitrack tape machines with appropriate equipment. The code is placed on one of the tracks on the tape. It is the code that sounds like a diseased choo-choo letting off steam if played through the speakers. Since position is encoded, this code can sync up at any point in the work, providing the equipment can do it. It is the most accurate analog sync system available.
Frequency Shift Keying (FSK)
Frequency Shift Keying is actually used for almost all forms of synchronization, including SMPTE time code. But this is a system with the name FSK, which records timing impulses on one track of the tape. It works only if everything is started from the beginning of the work, because it encodes timing, not position. The code sounds like a diseased choo-choo chugging if played through the speakers.
MIDI Clock
The Musical Instrument Digital Interface (MIDI) was developed so that one musician can control many sounds. Included in this is the ability to record the actions the musician performed to produce the sounds, and reproduce them later. In order that all of these sounds are produced at the right time, the MIDI Clock keeps track of the timing, so all of the notes that are supposed to sound together actually do. MIDI Clock can also synchronize equipment. It comes in two flavors, with and without the Song Position Pointer. Without the Song Position Pointer, the work must be started at the beginning for all of the parts to be in sync.
The fly in the MIDI ointment is that the frequency that MIDI operates at (32.1 KHz) is too high to be recorded to tape. Therefore, a CoDec (coder-decoder) is needed to convert this high frequency signal to something that can be recorded to tape, and back again for playback. Usually FSK codes are used. SMPTE can be used only if Song Position Pointer is present. Another problem with MIDI Clock is that the speed of the code changes with the tempo of the song, making it useless for some applications.
MIDI Time Code (MTC)
To facilitate a larger variety of MIDI systems, MIDI Time Code was developed. It is independent of the tempo of the song, and has tighter control over synchronization. It also keeps track of where in a song it is, so machines can sync up at places other than the beginning. Since the MIDI speed is still too fast, the time code must be recorded on analog tracks using a CoDec (a different one, since MIDI Clock is not the same as MIDI Time Code). Usually it is converted to SMPTE Time code.
One important factor in synchronization is that you must always use the same synchronizing device with the same recording. The exception is if SMPTE code is used. There some interchangeability is available.
Another important factor is that one device must be the master device, and the others must be capable of slaving themselves to the master. The slaving operations are a lot harder to implement in a machine, so many multitracks have only the master capability, expecting the other device to be the slave. On the other hand, most computer programs used for sound recording or MIDI are quite able to slave themselves, since slaving software is much easier to write than slaving hardware is to build.
These are the most frequently asked questions about synchronization:
Q: My cassette multitrack has a SYNC jack on the back. Does this mean I can synchronize two of them together?
A: If it is an RCA jack, no. That is used to play back the FSK or SMPTE signals recorded on the tape, which are used to synchronize other devices. In other words, the cassette multitrack must be the master device.
If the machine has a multipin synchronization port and electronic transport controls, then it might be capable of being slaved to another machine. See the instructions to find out for sure.
Q: Why is sync really necessary? Why can't I just start both machines at the same time for both record and playback? Every time I try this, the parts get out of sync before the song is over. With today's good electronics, I don't think this should happen.
A: Unfortunately, there are slight environmental differences that can unsynchronize even the best multitracks. Temperature differences can cause one machine to run at a slightly different speed. Slight variations in line voltage can affect each transport differently. Even dirt on the capstans can change the speed enough to unsynchronize two recorders. So we use the synchronizers to push the wandering decks back into alignment.
In order to keep phase integrity over a 4-minute song, the machines would have to have a speed accuracy of .00001 percent. They would also have to be started within 10 microseconds of each other.
To understand this better, think of the multitracks as musicians in an orchestra. They have to see the conductor's leading baton, and hear the other instruments play, in order to stay in sync. Your tape recorders are like an orchestra of blind and deaf musicians, trying to play a piece together.
Q: Why can't I just record the MIDI codes directly?
A: The speed of the MIDI standard is too fast. There are tones as high as 50 KHz there, and those can't be recorded on an audio recorder.
Q: I hooked up the MIDI. Why don't I hear anything?
Q: Can I record my voice on MIDI?
A: MIDI does not carry sound. It carries the instructions of what notes to play. Think of it as an electronic player-piano roll, with the instructions of which keys to press, and when, but with no control over what the actual piano that plays the roll will sound like. You still need audio cables and an audio recording device to handle actual sounds.
Q: I got a DIN splitter cord to hook up two MIDI instruments to one computer. Now none of them work. Why?
A: MIDI is a current loop system, and the output supplies only enough current to work one input. To do more inputs, you need a MIDI Thru box, which electronically replicates the MIDI signal at each of several outputs.
The THRU connection on a MIDI instrument is an electronic replication of the signal present on the IN connector, and does the same thing as the MIDI Thru box.
Q: How can I synchronize my multitrack to my computer?
A: Almost ANY analog multitrack recorder can be synched to a computer audio and sequencer program. This is done by making the recorder the master and the computer program the slave. Here's what you do:
Write your MIDI parts for the sequencer. Leave a few blank measures at the beginning to allow time for sync lock, and a few at the end to avoid errors that an abrupt cutoff of sync might cause (like a last note that won't quit playing). You can also build in a countoff so the musicians know when to start playing.
This is also the time to record any MIDI parts that are actually played by a musician.
The sequencer will have to be set up as a master for this first step, but switched to slave mode for the other steps.
Connect the CoDec Audio Out to the Record In for the sync track on the multitrack. This is usually the highest track number, but use the track the manufacturer designates if one is so indicated.
These should be the only MIDI connections.
Record the MIDI sync track while playing the song on the sequencer. There must be no noise reduction on the sync track.
Once you have done this, you may not make any more changes to the song in the sequencer that affect timing. If you do make such changes in the song, you will have to redo this step and everything that was done after it.
Connect the CoDec MIDI Out to the MIDI IN on the computer.
NOTE: Some CoDecs take their power from the computer. These may need the MIDI connection from the Computer MIDI Out to the CoDec MIDI In to supply power to the CoDec. If so, provide this connection.
These should now be the only MIDI connections.
If the sequencer is being used to control MIDI instruments, connect the MIDI Out on the computer to the MIDI In of the first instrument, and daisy chain the rest of the instruments together, with MIDI Thru connected to the next MIDI In. Don't forget to connect the Audio Out of each instrument to a mixer input, so you can hear the MIDI instruments play.
NOTE: If the MIDI Out is already in use for the CoDec, you can move the CoDec to the end of the chain if the connection is just being used for power supply. Otherwise, you will need a MIDI Thru box, which is an electronic version of a splitter cord. Splitter cords cannot be used in MIDI because it is a current loop system.
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