REDUCING VIBRATION INDUCED RECORDING NOISE

Abstract: A system for recording and replaying information in which noise caused by vibration of the system is eliminated. Two channels are used, one to record the input information, and the second to record a constant input signal. The first channel signal is then divided by the second channel signal to give an output signal free of vibration induced noise.

Description: I . REDUCING-VIBRATIQN-INDUCES-RECORDING-NOISE This invention relates to an arrangement for use with recording devices using discs or tape to reduce background noise caused by vibrations to the recording apparatus. In field applications, particularly where signal monitor ing is being carried out, the signal is often subject to distortion by vibrations which the recording apparatus is subjected to. These vibrations affect the frequency of the signal and make analysis and monitoring difficult. One attempt to reduce background noise has been proposed in Australian Patent 498,339. This patent proposes an informa tion transmission system in which an input information signal is recorded in a first channel of a record medium so that sai information signal plus a noise and distortion component becomes present in said first channel characterized in that the signal present in said first channel is read therefrom an combined with the input information signal in such manner as to substantially cancel the information signal present in the signal read from said first channel and produce a compensatio signal correlated to said noise and distortion component which compensation signal is recorded in a second channel of said record medium, and that the signal present in said first channel is subsequently read therefrom, and a signal derived from the second channel is combined with said signal sub¬ sequently read from the first channel in such a manner as to substantially cancel the noise and distortion component present in said signal subsequently read from the first channel. This method requires a delay of a portion of the signal and comparing the signal with the delayed signal to cancel out the signal to leave a noise signal which is subsequently subtracted from the information signal. This specification does admit that tape speed corrections will need to be made where motor speed variations exist. An object of the present invention is to provide a simpler means of reducing noise. To this end the present invention provides an informatio transmission system in which an input information signal is recorded in a first channel of a record medium and a second constant input signal is recorded in a second channel of said record medium characterized in that the first recorded input signal is divided by the second recorded signal to provide an output signal which is substantially free of any noise produced by vibrations to which the system is subjected. This invention is based on the discovery that the vibra- tions to the system have a multiplying effect on the input signal. By allowing the vibrational noise to be recorded on both an information signal channel and a constant signal channel a simple means is provided for effectively cancelling out the component in the information input signal. A preferred embodiment of the invention will now be described with reference to the drawings in which figure 1 is a block diagram of the preferred recording system of thi invention, figure lb is a block diagram of the playback system, figures 2a and 2b illustrate portions of the circuits respectively of the preferred form of the invention. The system is presented as an attachment to a recording device, in this case, a tape recorder 20 with stereo output. The first channel carries the information signal while the second channel carries the constant reference signal. Where low level signals are being recorded an amplifier 21 is required to amplify the signal. The output of the voltage to frequency converter 22 (voltage controlled oscillator) is not constrained to be of any particular shape. The only con¬ straint is that after replay from the tape recorder, a wave- shape which is compatible with the frequency to voltage converter is obtained. This also applies to the reference oscillator 23 which generates the reference signal 54. The voltage to frequency 22 and frequency to voltage convert¬ ers 25,26 are only required when used with tape recorders tha do not contain FM recording facilities. The first channel (input channel) voltage to frequency converter 22 is only required if the input signal frequency range is incompatible with the tape recorder being used. A low pass filter is used to remove any unwanted frequencies in the lower range, but, in general, this will depend on the purpose to which the signal receiving system is being put. An inverter is used to invert the reference signal which is subsequently divided into the information signal in the divider circuit to give the noise reduced output signal. Referring to the circuits of figures 2a and 2b, the difference signal SI is amplified by the required amount and applied to the voltage to frequency converter (VFC) input (S2). This low frequency signal is converted to a signal of convenient frequency (S3) and applied to channel 1 of the tape recorder. The signal S3, may be adjusted to a particular frequency at zero input voltage and also for scale factor, i.e. change in frequency for change in voltage level. A suitable frequency is selected for the reference oscillator Signal (S4) and applied to the tape recorder second channel. On playback the signals from both channels are recon¬ verted by the frequency to voltage converters 25 and 26 to low frequency signals (S7, S8). In figure 2b the signals from the recorder 55 and 56 are amplified by amplifiers 27 and 28 before conversion. The input channel signal (S7) would, if not corrupted by tape speed variations, be identical to the input signal (S2). The reference channel signal (S7) would ideally be a constant DC voltage which is converted to a negative DC voltage (S9) for compatibility with the "X" terminal of the AD533 divider circuit 29. The divider output signal (S10) will be an identical replica of the input signal S2 free of tape speed variation induced errors. The inverter is only required with a certain type of divider circuit (of which the AD533 is one). It is possible to use dividers for which the inverter is not necessary. It is not necessary to connect the reference oscillator to the second channel, however, connection of both signals to the same tape recorder channel requires additional circuitry. It can be seen that the system of this invention conven¬ iently eliminates noise due to vibration of a recording device.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. An information transmission system in which an input information signal is recorded in a first channel of a record medium and a second constant input signal is recorded in a second channel of said record medium charact¬ erized in that the first recorded input signal is divided by the second recorded signal to provide an output signal which is substantially free of any noise produced by vibrations to which the system is subjected. 2. An information transmission system as claimed in claim 1 connected electrically to a tape recorder having a stereo output. 3. An information transmission system as claimed in claim 1 or 2 in which the input signal amplified. 4. A recording and playback device comprising means for receiving signal means for recording said signal on a first channel of a recording medium, means for generating a constant signal, means for recording said constant signal on a second channel of said recording medium, an electrical divider circuit for dividing the signal recorded on said first channel by the signal recorded on said channel to produce an output signal which is substantially free of any noise produced by vibrations to which the recording and playback device is subjected. 5. A device as claimed in claim 4 in which said received signal is amplified.

Inventors: HAMILTON NEIL ROBERT, HAMILTON, NEIL, ROBERT
Applicants: COMMW OF AUSTRALIA, THE COMMONWEALTH OF AUSTRALIA CARE OF THE DEPARTME
Application year: 1983
Main classification: G11B5
IPC codes: G11B20