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If you are confronted with a Forensics Audio Tape which has been erased, there is the possibility of recovering a portion of that signal. This methodology relies on the possibility (probability) that some misalignment exists between the tapes recorded tracks and the erase head alignment. Often the recorder which made the original tape is a different machine than the one that was used to erase the tape, so the likeleyhood of perfect alignment between the erase head and the recorded tracks is limited. And, even if the same machine that made the tape was used to erase it, there is still some chance that there had been a misalignment between the erase head and the recorded tracks. The technique for finding some of the erased audio can be applied to a variety of analog tape types including:
1. Reel-to-Reel
2. Compact Cassette
3. Micro Cassette
You must be willing to gain access to the play head of your tape player to attempt recovery, unless you purchase a special machine designed to do this (about $5,000.00 for a JBR Multi-channel Microcassette deck as an example - - - available from Tracer Technologies).
When working with a Forensics tape, erased or otherwise, I always recommend clipping the wires on the erase and record head or disabling the machines bias oscillator circuit. I usually cut the pcb track which supplies Vcc+ to the bias transformer primary center tap connection. On a three head machine, the erase head is the first one along the path of tape travel, the record head is the middle one while the last head towards the end of tape travel is the playback head. With that said, the idea here is to find the portion of the original audio track that was right on the edge of the tolerance of the erasing machines erase head vertical position. By moving the playback head up and down (there are usually three and sometimes four screw adjustments on this playback head which can be turned with a de-magnetized jewelers screwdriver or "twiddle stick").
Scan the tape by moving the playback head position up and down with respect to the erased tape while it is playing and while you are listening to the same. It is a good idea to note the positions of the original playback head position by way of the screw adjuster positions. First, try moving the tape head up a bit and listen carefully for some audio signal content to appear. (Keep note of the number of turns and the direction {CW vs. CCW} that you rotate any given adjuster screw.) You can move it as much as around 1/8th of the total tape width as a general rule of thumb. If that does not reveal any audio, return the screw adjustments to their original positions and then move the head in the opposite direction, while searching for some audio. If you find a position having a bit of audio, you may find that it is very noisey, but that can be dealt with later. Just transfer that audio signal to your computer hard drive so that you can use the Diamond Cut Forensics audio software tools to enhance the signal at a later time.
Repeat that process on both sides of the tape until the entire recoverable signal is captured. When you are done, be sure to return the playback head to its original position. This can be accomplished with the use of an azimuith alignment tape or another method.
If you do not find a signal anywhere during the playback head scan procedure, it could be that the tape was erased via a bulk tape eraser in which case the signal will not be recoverable.
1. Reel-to-Reel
2. Compact Cassette
3. Micro Cassette
You must be willing to gain access to the play head of your tape player to attempt recovery, unless you purchase a special machine designed to do this (about $5,000.00 for a JBR Multi-channel Microcassette deck as an example - - - available from Tracer Technologies).
When working with a Forensics tape, erased or otherwise, I always recommend clipping the wires on the erase and record head or disabling the machines bias oscillator circuit. I usually cut the pcb track which supplies Vcc+ to the bias transformer primary center tap connection. On a three head machine, the erase head is the first one along the path of tape travel, the record head is the middle one while the last head towards the end of tape travel is the playback head. With that said, the idea here is to find the portion of the original audio track that was right on the edge of the tolerance of the erasing machines erase head vertical position. By moving the playback head up and down (there are usually three and sometimes four screw adjustments on this playback head which can be turned with a de-magnetized jewelers screwdriver or "twiddle stick").
Scan the tape by moving the playback head position up and down with respect to the erased tape while it is playing and while you are listening to the same. It is a good idea to note the positions of the original playback head position by way of the screw adjuster positions. First, try moving the tape head up a bit and listen carefully for some audio signal content to appear. (Keep note of the number of turns and the direction {CW vs. CCW} that you rotate any given adjuster screw.) You can move it as much as around 1/8th of the total tape width as a general rule of thumb. If that does not reveal any audio, return the screw adjustments to their original positions and then move the head in the opposite direction, while searching for some audio. If you find a position having a bit of audio, you may find that it is very noisey, but that can be dealt with later. Just transfer that audio signal to your computer hard drive so that you can use the Diamond Cut Forensics audio software tools to enhance the signal at a later time.
Repeat that process on both sides of the tape until the entire recoverable signal is captured. When you are done, be sure to return the playback head to its original position. This can be accomplished with the use of an azimuith alignment tape or another method.
If you do not find a signal anywhere during the playback head scan procedure, it could be that the tape was erased via a bulk tape eraser in which case the signal will not be recoverable.
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