High quality tape decks such as the ones used in sound studios require frequent adjustments in order to optimize performance. Two of the most common adjustments are adjusting the azimuth of the recording and playback head and adjusting the recording and playback levels. Although these adjustments are necessary on a very frequent basis, preferably before each recording session in a sound studio, these adjustments have required expensive instruments and a relatively high degree of expertise in adjusting tape decks and operating laboratory instruments.
In order to adjust the playback voltage level, the conventional technique is to play a test tape in the tape player. The test tape will have numerous tones recorded on it at a magnetic flux density that should produce a nominal voltage level output. Most tape players have a nominal output voltage of +4 dbm (1.23 volts), but -8 dbm (0.3 volts) and +2 dbm (1 volt) are also common nominal record and play levels for professional recorders. In order to measure these relatively low voltage readings, expensive volt meters are required when performing this adjustment using a conventional technique.
In some professional tape recorders, the recording head may be switched into a playback mode and the test tape may be played back through the recording head. Thus, the record level may be adjusted in the same manner as the playback level. However, in machines that do not have such feature, the record level may be adjusted by using an oscillator to produce an input signal of a selected frequency and voltage level which is recorded by the recording head on a tape and simultaneously played back through the playback head. Assuming the playback level has previously been adjusted, the output from the playback head will indicate the recording level of the tape deck and the record level may be adjusted to an appropriate level by monitoring the playback level. In order to perform this latter adjustment technique, an accurate oscillator must be available to the operator in order to produce the test signal.
The conventional technique for adjusting the azimuth of a playback head is to play a test tape having a manaural recording on the outermost two tracks of the tape. If the azimuth of the head is not properly aligned, the playback output signals from these two outermost tracks will be out of phase. In order to adjust the azimuth of the playback head, the playback output signal from the two outermost tracks are typically monitored on a single oscilloscope using two probes. The azimuth of the playback head is then adjusted until the output signals are phase synchronized.
The conventional technique for adjusting the azimuth of a record head is to input a manaural signal into the tape recorder, record this test signal on the two outermost tracks of a tape and play back these two outermost tracks through the playback head. Assuming that the azimuth of a playback had been previously adjusted, any phase difference between the two playback signals will be caused by the maladjusted azimuth of the record head. Thus, the azimuth of the record head is adjusted until the output playback signals from the two outermost tracks of the tape are synchronized. Again, conventionally, a two probe oscilloscope was necessary in order to monitor the relative phases of the two playback signals from the outermost tracks of the tape.
The primary drawback with the conventional techniques described above is that expensive laboratory equipment is required in order to perform the various adjustments. Also, considerable expertise in operating the test equipment and the tape deck were required in order to perform the adjustments, and most lab instruments have a visual output so that the technician must constantly watch the instruments while he is attempting to adjust the tape deck. When the tape deck's adjustment mechanisms are difficult to access, it is inconvenient for the operator to constantly view his instruments while attempting to adjust the tape deck.
Thus, a need has arisen for a simple and inexpensive instrument for use in adjusting the record and playback levels of a tape deck and for adjusting the azimuth of the recording and playback heads of a tape deck.