JBR MICROCASSETTE PLAYBACK UNIT
Unique features of this unit for conducting authenticity examinations:
The JBR Microcassette Playback Unit has two separate 1/4-track stereo playback heads. One head enters the face of the microcassette where the left felt pressure pad is located and the second head enters the face of the microcassette where the right felt pressure pad is located. The left head is used to play the left and right tracks of the microcassette. This unique custom design enables the JBR Microcassette Playback Unit to play approximately 3/4-inch of virgin tape since all known microcassette recorders have their record/play head enter the face of the microcassette on the right side. The forensic examiner can measure the noise level of this short segment of virgin tape and then use this data to determine if there are segments of tape in the recording that have never been recorded on.
In addition, the location of the left playback head enables our unit to reach operating playback speed and provides the electronics with sufficient time to stabilize before any transients placed on the tape when the microcassette was recorded passes over this head. Our unit can faithfully and accurately play back the record head and erase head transients placed on the beginning of a microcassette when it was recorded. No other known microcassette unit has this capability.
The standard right side 1/4-track stereo head plays back the side B left or right channel as side A is being played on the left head to determine if anything is recorded on side B (audio will be backwards).
A custom right side 1/4-track stereo playback head is available as an option and is mounted at the correct height to play back the guard band between sides A and B of the microcassette instead of the left or right track of side B. The guard band is where the top part of the taller erase head magnetic marks rise above the magnetic marks made by the record head. The JBR Microcassette Playback Unit is the only known microcassette playback unit that can simultaneously (displaced by 3/4-inch) play back the guard band while it is playing the left and right channels. The forensic examiner can use 3-channels of a 4-channel digital computer hard disk recording system to capture the left and right audio and the side A/B guard band. Playing the guard band enables the examiner to determine if the erase head marks are original (erase head tall) or a copy (record head tall).
A 4th channel of pre-amplification is available as an option with the custom right side 1/4-track playback head that enables the simultaneous playback of the right channel of the other side of the microcassette as it is playing as well as the side A/B guard band. If a recording is present on side B of the microcassette, it will be reproduced backwards. The computer system can reverse this waveform and the examiner can conduct a waveform analysis of the left and right channels of side A, the guard band, and the right channel of side B with all information in time sync since all channels were played at the same time. This a powerful capability that is not available on any known competitive unit.
The unit has the lowest wow and flutter of any known microcassette playback unit. When a tape is played back and copied into a digital hard disk recorder, the degradation added by the JBR unit to the original tape's wow and flutter is less than 0.10% rms wtd. This exceptionally low wow and flutter produces a sharper brighter sound.
The speed change from beginning of tape (BOT) to end of tape (EOT) is less than 0.3% on the JBR unit (± 4.5 Hz for a 3,000 Hz tone). This small speed change from BOT to EOT means that a notch filter used to filter out 180 Hz only needs to be 0.54 Hertz wide at the desired attenuation level (plus any speed drift in the original tape). This means that an enhancement filter does not have to be widened to accommodate our added speed change. If the speed change is 3% on other playback units, the filter would need to be widened by 5.4 Hertz. The wider the filter notch the more of the adjacent voice information the filter removes.
Wow and flutter, short term speed drift, and speed change from the BOT to EOT all greatly affect the performance for all fixed, tracking and adaptive filters. These specifications actually enable any filter to perform better on a tape played on the JBR unit than a competitor's unit.
The exceptional signal-to-noise capability of the JBR Microcassette Unit enables the play back of low level signal that cannot be faithfully played on other units. In summary, the JBR Microcassette Playback Unit is the highest performing microcassette playback unit available and actually enables the examiner to perform tests that cannot be conducted on any other know unit.
If you have a specialized or unique requirement, JBR Technology is fully capable of producing a customized unit to meet your needs.
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(Specifications Subject to Change Without Notice)
JBR Technology, Inc.
1971 Keswick Mews
Woodbridge, VA 22192