The invention relates to a system for monitoring a control signal carried by a recording medium as the medium moves past a monitoring location, and more particularly relates to a cue detection system for a magnetic tape bearing a cue signal together with other magnetic information, which detects the cue signal as the tape moves at greatly varying speeds past a cue monitoring head.
A cue tone signal is a signal recorded on a magnetic recording tape and is used to control a machine function which may be performed on the recording tape. For example, in a cassette tape loader in which empty cassettes are loaded with predetermined lengths of magnetic recording tape, a spool of tape to be cut and loaded into a plurality of cassettes will contain a cue tone signal at various locations on the tape for instructing the cassette loader to initiate a cutting and splicing operation at predetermined intervals on the recording tape. Thus, the tape loader is to ignore other magnetic information carried by the recording tape, but upon sensing the cue signal, the loader will perform a predetermined operation.
Thus, a cue detection circuit must ignore all recorded magnetic information and noise except the specific cue signal.
Heretofore, a cue tone signal has been recorded on a magnetic tape which is moved at a predetermined speed and, thus, during playback the speed must be maintained within certain limits so that the cue tone signal will be picked-up at a predetermined frequency. A band pass filter arrangement is then utilized within those limits for searching for the particular frequency of the cue tone in order to discriminate the cue tone signal from other recorded information. In some instances, the tape could be moved at a high speed and at a low speed of operation and, thus, two filters were necessary.
However, where the magnetic tape is moved at greatly varying speeds, the frequency of the recorded signals will vary in relation to the speed of the tape. Thus, the cue frequency will vary over a range of frequencies depending on the range of tape speeds. Thus, utilizing frequency to search for the cue signal becomes complicated as the recording tape takes on greatly varying speeds of movement during cue signal monitoring.
Similarly, the use of signal amplitude sensing to monitor cue signal occurence is complicated by tape movement at greatly varying speeds. The amplitude of the recording signal picked up from the magnetic tape will vary directly with the intensity of the magnetic signal and directly with the speed of the magnetic medium relative to the pick-up head. Thus, where the magnetic tape takes on greatly varying speeds, the amplitude of the signal being picked up from the tape will also greatly vary.
It is therefore an object of the present invention to provide a cue tone detection circuit for a recording medium which is moving at greatly varying speeds, despite the great variation in amplitudes and frequencies provided by the recorded cue signal via a cue pick-up head.