Method of recording identification signal on software recording medium

According to a method of recording identification signals on a software recording medium of the invention, an identification signal is recorded in a left channel track of a soft tape, and an inverted signal of the identification signal is recorded in a right channel track of the soft tape. Non-inverted program signals are in the right channel and left channel tracks. For this reason, the identification signal and the inverted identification signal cancel each other in a program play mode of the soft tape.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A method of recording identification signals on a software recording medium 
according to an embodiment of the present invention will be described with 
reference to the accompanying drawings. FIG. 1 shows a signal recording 
circuit for implementing the method of the first embodiment. Referring to 
FIG. 1, an input terminal 10 is connected to the noninverted input 
terminal of an amplifier 12. The inverted input terminal of the amplifier 
12 is grounded. The output terminal of the amplifier 12 is connected to an 
L-channel (Lch) head 14. The input terminal 10 is also connected to the 
inverted input terminal of an inverting amplifier 16. The noninverted 
input terminal of the inverting amplifier 16 is grounded. The output 
terminal of the inverting amplifier 16 is connected to a contact 20-B of a 
switch 20. The switch 20 comprises, for example, a relay switch. The 
switch 20 is connected to an R-channel (Rch) head 18. The output terminal 
of the amplifier 12 is connected to a contact 20-A of the switch 20. By 
way of simplicity, the gain of the amplifier 12 is assumed to be the same 
as the absolute value of the gain of the inverting amplifier 16. 
Furthermore, the Lch head 14 is assumed to have the same performance as 
the Rch head 18, and the track widths of the tapes to be recorded with the 
heads 14 and 18 are assumed to be the same. 
The operation of the signal recording circuit shown in FIG. 1 will now be 
described. A signal E10 shown in FIG. 2(a) is supplied from a signal 
source (not shown) to the input terminal 10. The amplifier 12 amplifies 
the signal E10 without shifting the phase thereof and generates a signal 
E12. The signal E12 has the same phase as the signal E10, as shown in FIG. 
2(b). The signal E12 is supplied to the Lch head 14. The Lch head 14 
records the signal E12 in an Lch recording track. Meanwhile, the signal 
E10 is also supplied to the inverting amplifier 16. The inverting 
amplifier 16 inverts the phase of the signal E10 and amplifies it to 
generate a signal E16. The signal E16 has the opposite phase to that of 
the signal E12, as shown in FIG. 2(c). The signal E16 is supplied to the 
switch 20. When identification signals are recorded on the soft tape, the 
switch 20 is switched to the position of the contact 20-B. In this state, 
the signal E16 is supplied to the Rch head 18 through the switch 20. 
However, when the other signal, i.e., the program signal is recorded on 
the soft tape, the switch 20 is switched to the position of the contact 
20-A. In this state, the signal E12 is supplied to the Rch head 18. The 
switching operation of the switch 20 is performed in response to a 
switching signal (not shown). The identification signals are thus recorded 
in the Lch and Rch recording tracks in the opposite phases. On the other 
hand, the program signals are recorded in the Lch and Rch recording tracks 
in the same phase. As described above, the absolute value of the gain of 
the inverting amplifier 16 is the same as that of the amplifier 12. The 
Lch head 14 has the same characteristic as those of the Rch head 18, and 
the Rch track width is the same as the Lch track width. The identification 
signal recorded in the Lch track has the opposite phase but the same 
frequency and amplitude as that of the identification signal recorded in 
the Rch track. The program signal recorded in the Lch track has the same 
phase, frequency and amplitude as that of the program signal recorded in 
the Rch track. 
A case is illustrated in FIG. 3 wherein the signals are recorded by the 
circuit of FIG. 1 in the recording tracks of the soft tape. Referring to 
FIG. 3, track regions Ta, Tb, Tc and Td are formed in a magnetic surface 
of a soft tape 22. A signal Ea as the inverted signal of an identification 
signal Eb is recorded by the Rch head 14 in the Rch track region Ta. The 
identification signal Eb is recorded by the Lch head 14 in the Lch track 
region Tb. Program signals Ec and Ed are recorded in the regions Tc and 
Td, respectively. The waveforms of the signals Ea and Ec recorded in the 
Rch track and the waveforms of the signals Eb and Ed recorded in the Lch 
track are illustrated in FIGS. 4(a) and 4(b), respectively. The signal Ea 
recorded in the region Ta has the opposite phase but the same frequency 
and amplitude as the signal Eb recorded in the region Tb. On the other 
hand, the signal Ec recorded in the region Tc has the same phase, 
frequency and amplitude as the signal Ed recorded in the region Td. When 
the soft tape recorded in this manner is played with a two-channel stereo 
head unit, outputs having the waveforms shown in FIGS. 4(a) and 4(b) can 
be obtained. However, when the soft tape of FIG. 3 is played with a 
monaural head, or when the outputs are reproduced with the two-channel 
stereo head unit and combined, a signal having a waveform shown in FIG. 
4(c) can be obtained. The signal Ea cancels the signal Eb, and the 
resultant signal level becomes zero. On the other hand, when the signals 
Ec and Ed are combined, the resultant signal has the same phase and twice 
the amplitude as the signal Ec or Ed. According to the soft tape recorded 
by the method according to the present invention, when a monaural 
tape-recorder is used, the identification signals cannot be reproduced, 
but other signals (e.g., program signals) can be reproduced. However, when 
a stereo tape-recorder is used, both the identification and program 
signals can be reproduced. In general, cassette tape-recorders for 
computer soft tapes have monaural heads. As a result, the identification 
signals cannot be reproduced. When a monaural/stereo dual-mode cassette 
tape-recorder is used, the identification signals cancel each other when 
the monaural mode is selected. In this manner, in the play mode, only the 
program signal Ec+Ed is reproduced, but the identification signal Ea and 
Eb cancel each other. Even if the frequency and level of the 
identification signals are arbitrarily selected, these signals will not be 
mixed with the program signals. The identification signals recorded on the 
soft tape 22 will not adversely affect the reproduced program signals. 
When identification signals must be reproduced, signals recorded in one of 
the Lch and Rch tracks are reproduced or one of the reproduction signals 
in the two tracks is inverted and thereafter combined with another 
reproduction signal (i.e., substracted). When one reproduced output is 
phase-inverted and the resultant signal is combined with the other 
reproduced output, the program signal components cancel each other. On the 
other hand, the identification signal component Ea+Eb has a doubled 
amplitude, thereby producing an identification signal component with a 
sufficient level for easy detection. Therefore, during the manufacture of 
the soft tapes, the contents of the soft tapes can be easily checked. 
FIG. 5 shows signal recording regions of a magnetic tape recorded according 
to a method of recording identification signals on a soft tape according 
to a second embodiment of the present invention. A soft tape 24 has four 
tracks. Identification signals Ef, Eg, Eh and Ei are recorded in track 
regions Tf, Tg, Th and Ti, respectively. FIGS. 6(a) to 6(d) are waveforms 
of the signals Ef, Eg, Eh and Ei recorded in the track regions Tf, Tg, Th 
and Ti, respectively. When the signals Ef, Eg, Eh and Ei having different 
phases as shown in FIGS. 6(a) to 6(d) are combined, the signal Ef cancels 
the signal Eg, and the signal Eh cancels the signal Ei. For this reason, 
the identification signals cannot be reproduced with a monaural or 
two-channel stereo head. When the identification signals must be 
reproduced, only the signal Ef, for example, is reproduced. Alternatively, 
the reproduced outputs of the signals Ef and Eg may be combined after 
inverting the one reproduced output thereof. The phase of the signal Ef is 
shifted from that of the signal Eh, and the phase of the signal Eg is also 
shifted from that of the signal Ei. However, the phase of the signal Ef or 
Eg may be the same as that of the signal Eh or Ei. 
In the above embodiments, the soft tapes comprise 2- and 4-track tapes. 
However, the present invention is not limited to these types of soft 
tapes. The number of tracks may be arbitrarily selected. In addition, the 
amplitudes, frequencies and phases of identification signals recorded in 
the tracks may differ from each other. It is only essential for the 
reproduced identification signal component to have a sufficiently low 
level as to be neglected. Similarly, tracks of a soft tape may have 
different widths, and only some (e.g., two tracks) of the tracks (e.g., 
four tracks) may be used for recording identification signals. On the 
other hand, since the program signals have the same phase, they will not 
cancel each other upon reproduction. In order to reproduce the 
identification signals, the following processing is performed. The 
identification signals recorded in the opposite phases are reproduced 
separately. One of the reproduced signals is inverted and combined with 
the other reproduced signal to produce the indentification signal. In this 
case, the program signals cancel each other. The signals Ec and Ed of the 
same amplitude, frequency and phase are recorded in the regions Tc and Td 
of FIG. 3, respectively. However, the present invention is not limited to 
the above recording. For example, an identification signal sin .omega.t 
may be recorded in two of the three tracks, and identification signals 
-2sin .omega.t may be recorded in the remaining track. When these three 
identification signals are reproduced by a single monaural head, the 
identification signals can cancel each other. 
In the embodiment shown in FIG. 3, the regions Ta and Tb for the 
identification signals are independent of the regions Tc and Td for the 
program signal. However, the track region distribution is not limited to 
this. For example, in a soft tape 26 shown in FIG. 7, the identification 
signals and the program signals may be combined and recorded in regions Tl 
and Tm. Referring to FIG. 7, the regions Tj and Tk are the regions in 
which only the program signals are recorded. The regions Tl and Tm are 
regions in which the identification signals and the program signals are 
recorded. In this case, when the identification signals recorded in the 
regions Tl and Tm are reproduced with a monaural head, they cancel each 
other since the identification signals have the opposite phases. On the 
other hand, the program signals are combined and reproduced. According to 
the recording method of FIG. 7, the soft tape can be more effectively used 
than in the case in which the program signals and the identification 
signals are recorded separately. It should be noted that the 
identification signals can also be recorded together with the program 
signals in an overlapped manner in the embodiment shown in FIG. 5. A 
method for identifying the contents of recorded program signals by the 
reproduced identification signals, can be implemented through conventional 
techniques in which such identification signals are recorded on a common 
medium with the identified program signals. For example, names of programs 
or names of entire soft tapes can be recorded on a soft tape as 
identification signals in the form of a human voice. Then, according to 
the present recording/reproducing method, only the identification signals 
in one of the recording channels or tracks is reproduced to identify the 
program name by way of the reproduced signal. The reproduced 
identification signal also can be monitored with an oscilloscope to detect 
the names of the programs. Spot signals can be recorded as identification 
signals, and then reproduced to specify the types of recorded programs. 
In the embodiments shown in FIGS. 3 and 5, the identification signals and 
program signals are not limited to specific types. For example, 
amplitude-modulated (AM) signals, frequency-modulated (FM) signals, and 
phase-modulated signals can all be used as identification and program 
signals. In addition, the identification and program signals may be analog 
or digital signals. 
In the above embodiments, the software recording medium comprises a 
magnetic-tape, especially a cassette tape. However, any other software 
recording medium such as an optical disk can be used in place of the soft 
tape. FIG. 8 shows an embodiment using an optical disk 28 to which the 
present invention is applied. FIG. 8 is an enlarged plan view showing part 
of the optical disk 28. Pits 34 are formed in first and second pregrooves 
30 and 32. Referring to FIG. 8, the first pregroove 30 has no pit in the 
position corresponding to a position of the second pregroove 32, and vice 
verse. More particularly, when a signal 0010010 . . . is recorded in the 
first groove 30, a signal 1101101 . . . is recorded in the second groove 
32. It should be noted that the pits 34 correspond to a signal of logic 
level "1". An inverted signal of a signal recorded in the first pregroove 
30 is recorded in the second groove 32. In this manner, the bits of the 
identification signal recorded in the first groove 30 have an inverted 
logic level as compared to the bits of the identification signal recorded 
in the second groove 32, so that these identification signals cancel each 
other. The present invention can also be applied to another software 
recording medium such as a magnetic tape, a disk and a floppy disk.