Channel division recording/reproducing apparatus

A channel division recording/reproducing apparatus is provided for dividing an input signal into signals for a plurality of channels through an Hadamard transformation, frequency modulating the signals of the respective channels and recording them and, after demodulating the recorded signals for the respective channels, subjecting the demodulated signals to an Hadamard inverse transformation and reproducing the input signal. Out of the Hadamard-transformed signals, the signal on the channel of the minimum frequency band is separated by a filter from the input signal and the separated signal processed by an additional Hadamard transformer and Hadamard inverse transformer and frequency modulated with a modulation index greater than the original signal and with a carrier of a lower frequency. An impovement in signal-to-noise ratio is thereby obtained. When recording a video signal, the "beat" phenomenon between the video signal and carrier signal is reduced while the signal-to-noise ratio of the video signal as a whole is improved.

BACKGROUND OF THE INVENTION 
This invention relates to a channel division recording/reproducing 
apparatus adapted to divide a broad band signal such as a video signal 
into narrow band signals for a plurality of channels for recording and 
reproduction. 
In order to record a video signal such as a television signal, etc., it is 
generally necessary that the frequency band of a recording system be made 
broad enough to meet that of the video signal. In an attempt to make the 
relative speed of a magnetic head and magnetic tape higher, for example, 
in a video tape recorder both the tape and the head may be rotated, but a 
structural difficulty is often encountered by doing so. Where, on the 
other hand, the magnetic head is not rotated, the travelling speed of the 
tape has to be made higher, presenting a structural problem. Moreover, 
more tape has to be used. Recently, attempts have been made to divide a 
video signal into narrow band signals for a plurality of channels and 
record them through a corresponding number of fixed heads. As such a 
division method, an Hadamard transformation is known which divides an 
original signal by sequency components similar to frequency components 
into a plurality of channel signals. The Hadamard transformation is one 
kind of an orthogonal transformation and an input signal is 
Hadamard-transformed using a Walsh function. Now suppose that a 2 MHz 
luminance signal is used as an input signal and that the Walsh function is 
a function of the eighth order. Then, the luminance signal is, after 
Hadamard transformation, divided into narrow band signals of eight 
channels of 250 KHz. The narrow band signals are frequency modulated for 
the respective channels and supplied to the magnetic heads. Now suppose 
that the carrier frequency of the respective modulators is set, for 
example, at 700 KHz, a value sufficiently higher than 250 KHz. Even if in 
this case a greater frequency deviation is taken, a modulation index can 
be made greater without involving a "beat" phenomenon between the 
luminance signal and the carrier signal, thus leading to an improvement in 
the signal-to-noise ratio (S/N ratio) as well as in the quality of a 
luminance signal recorded. In actual practice, however, the frequency of 
the carrier signal can not be sufficiently high in view of a relation 
between the travelling speed of the magnetic tape and the wavelength of 
the luminance signal. If the modulation index is made greater and a 
frequency deviation is made greater to improve the S/N ratio for a too low 
carrier frequency, a "beat" phenomenon occurs between the luminance signal 
and the carrier signal, thus degenerating the S/N ratio. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to provide a channel division 
recording/reproducing apparatus which can divide a broad band signal into 
narrow band signals for a plurality of channels and record and reproduce 
an input signal with a better S/N ratio. 
According to this invention there is provided a channel division 
recording/reproducing apparatus comprising means for dividing an input 
signal into first and second frequency signals, first orthogonal 
transforming means for transforming the first frequency signal into narrow 
band signals for a plurality of channels, second orthogonal transforming 
means for transforming the second frequency signal into narrow band 
signals for a plurality of channels, a narrow band signal on the channel 
of a minimum frequency band being equal in frequency to the first 
frequency signal, means for frequency modulating the output signals of the 
first and second orthogonal transforming means for the respective channels 
and recording them on a recording medium, and means for demodulating the 
recorded signals on a recording medium for the respective channels, 
subjecting the demodulated signals to an orthogonal inverse transformation 
for the first and second frequencies and reproducing the first and second 
frequency signals.

DETAILED DESCRIPTION OF THE INVENTION 
An input terminal 10 is connected to a low-pass filter 12 and high-pass 
filter 14. A video signal from an image pickup camera or television 
receiver is supplied to the input terminal 10. Now suppose that the video 
signal has a frequency of 2 MHz and that the pass bands of the low- and 
high-pass filters are below 250 KHz and in excess of 250 KHz, 
respectively. The output of the low-pass filter 12 is connected to an 
Hadamard transformer 16 of the second order and the output of the 
high-pass filter 14 to an Hadamard transformer 18 of the eighth order. The 
two output channel signals of the Hadamard transformer 16 are supplied 
through frequency modulators 20-1 and 20-2 to a record/reproduce circuit 
22 and the eight output channel signals of the Hadamard transformer 18 are 
supplied through frequency modulators 20-3, 20-4 . . . and, 20-10 to the 
record/reproduce circuit 22. The record/reproduce circuit 22 has ten fixed 
magnetic heads each corresponding to a respective channel. Signals 
detected at the respective magnetic heads are supplied respectively 
through amplifiers 24-1, 24-2 . . . and 24-10 to frequency demodulators 
26-1, 26-2 . . . and 26-10. The outputs of the frequency demodulators 26-1 
and 26-2 are supplied to an Hadamard inverse transformer 28 of the second 
order and the outputs of the frequency demodulators 26-3, 26-4 . . . and 
26-10 to an Hadamard inverse transformer 30 of the eighth order. The 
output of the Hadamard transformer 28 is connected to one input of a mixer 
32 and the output of the Hadamard inverse transformers 30 to the other 
input of the mixer 32. The output of the mixer 32 is connected to an 
output terminal 34. 
The operation of the embodiment will now be explained below. 
A signal of 250 KHz is supplied to the Hadamard transformer 16 to produce 
0-125 KHz and 125-250 KHz channel signals. Thus, frequency bandwidths of 
125 KHz are provided. Even if the frequency of a carrier signal is not 
high enough, when a greater frequency deviation is made, the frequency 
modulators 20-1 and 20-2 can have a greater modulation index without 
involving the beating between video and carrier signals, leading to an 
improvement in S/N ratio. A 2 MHz signal is supplied to the Hadamard 
transformer 18 to produce eight 250 KHz channel signals. Since, however, 
the 0 to 250 KHz signal is cut off by the high-pass filter 14, no signal 
appears from a first output channel of the Hadamard transformer 18. The 
250 to 500 KHz, . . . and 17,500 KHz to 2 MHz signals appear from the 
second, . . . and eighth output channels, respectively. As the signals of 
a bandwidth of 250 KHz are supplied to the modulators 20-4 . . . and 
20-10, if a greater frequency deviation is taken to improve the S/N ratio, 
a "beat" phenomenon occurs between the video signal and the carrier 
signal. For this reason, no greater frequency deviation can be made, 
failing to improve the S/N ratio. In an orthogonal transformation such as 
the Hadamard transformation, however, the energies of signals after 
transformation are concentrated on low frequency channels. Even if, 
therefore, the S/N ratio of the high frequency channels of the video 
signals is degenerated, the S/N ratio of the signal suffers no substantial 
influence. That is, if the S/N ratio of only the low frequency channels of 
the video signal is improved as in this embodiment, it contributes to the 
video signal as a whole and thus the S/N ratio of the video signal as a 
whole is improved. In this way, the video signal is divided into a 
plurality of channel signals, which are recorded, through the respective 
magnetic head, on a magnetic tape for the respective channel. 
During the reproduce mode, signals are detected through the magnetic heads 
for the respective channel in a way reversed with respect to the record 
mode, and signals of 0 to 125 KHz and 125 to 250 KHz are supplied through 
the frequency demodulators 26-1 and 26-2 to the Hadamard inverse 
transformer 28 to permit the output of the low-pass filter to be 
reproduced. Signals of 250 to 500 KHz, . . . and 17,500 KHz to 2 MHz are 
supplied respectively through the frequency demodulators 26-4, . . . and 
26-10 to the Hadamard inverse transformer 30 to permit the output of the 
high pass filter 14 to be reproduced. The outputs of the Hadamard inverse 
transformers 28 and 30 are mixed and an input video signal is reproduced 
at the output terminal 34. Although the modulator 20-3, amplifier 24-3 and 
demodulator 26-3 for the first channel (0 to 250 KHz) associated with the 
Hadamard-transformed frequency components of the higher video signal (250 
KHz to 2 MHz) are shown in the drawing, they may be omitted. A proper 
orthogonal transformation, such as an Haar transformation, other than the 
Hadamard transformation may be used.