Pitch control apparatus for sound reproducing system

In a recording medium playback device, such as a tape recorder, the playback speed is changed from the speed used during recording but the sounds and voices being reproduced can be listened to at the normal pitch, as if the playback tape speed was the same as the recording speed. A frequency generator (FG) system is not required and the playback signal is converted in pitch based on a capstan motor drive signal that is converted to a voltage value and that controls a pitch converting circuit. Alternatively, the pitch converting circuit is controlled by a signal derived from a speed control system, whereby the capstan motor speed is controlled by the user of the tape recorder. By converting the pitch of the playback signal in this way a recording of a conference, for example, can be scanned at high speed yet the reproduced voices are provided with a normal pitch.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a sound reproducing apparatus 
such as a tape recorder and, more specifically, to a playback apparatus 
capable of performing a pitch conversion of an audio signal reproduced at 
a speed other than the speed at which it was recorded. 
2. Description of the Background 
In electronic appliances, for instance, tape recorders and tape players, 
not only is the rotation frequency or number of revolutions of the motor 
controlled to drive the magnetic tape at the rated tape speed, but the 
rotation frequency of the motor also can be varied in response to a 
variable tape speed operation performed by the user. 
Furthermore, in some other electronic appliances there is provided a pitch 
or frequency converting process that is carried out with respect to the 
reproduced audio signal from the magnetic tape and the like in accordance 
with a pitch converting amount provided by the user, thereby increasing or 
decreasing musical intervals, that is, the pitch of the sounds, in the 
reproduced sound signal. 
On the other hand, when the tape drive speed is changed from that at which 
the sounds were recorded, the pitch of the sounds being reproduced is also 
changed. Thus, there is the great possibility that one can hardly listen 
to and understand such reproduced sounds whose pitch is varied. As a 
consequence, it would be preferable that the above-described pitch 
conversion is performed to obtain such sounds having easy listening 
musical intervals, even during high-speed reproduction or low-speed 
reproduction. For instance, in the case of a tape on which a conference or 
business meeting has been recorded, when this tape is reproduced or played 
back at high speed the musical intervals of the conversational voices 
becomes much higher than normal, so that the contents of the recorded 
voices cannot be easily grasped. To the contrary, when the pitch 
conversion of the voice output is performed in such a manner that the 
musical interval of this voice output is lowered, everyone can listen to 
the reproduced voice with easy listening musical intervals, for example, 
with the musical interval at the rated tape drive speed. 
At this time, the pitch converting amount is not manually controlled by the 
user, but a preselected pitch converting amount is automatically set in 
response to changes in the amount of the tape drive speed. Even when the 
user changes the tape drive speed, useful appliances could be realized if 
such sounds having the musical intervals obtained during rated tape drive 
speed are reproduced as the output. 
In order that a predetermined pitch converting amount is automatically set 
in response to the amount of change of the tape drive speed, all 
previously proposed systems require a mechanism capable of detecting the 
tape drive speed. For example, a rotation frequency detecting mechanism 
such as a frequency generator (FG) is mounted to the motor that provides 
the tape drive, and a pitch control signal for setting the pitch 
converting amount in response to an output of this rotation frequency 
detecting mechanism is produced. To detect the position of the slider of a 
variable resistor used in a motor servo circuit to control the tape drive 
speed, a detecting variable resistor is provided which is mechanically 
coupled to the speed control variable resistor, and then a pitch control 
signal is produced based on the resistance value of this detecting 
variable resistor. 
Since such a detecting mechanism is required when a predetermined pitch 
converting amount is automatically set in response to the change amount of 
the tape drive speed, there are disadvantages in view of manufacturing 
cost and package spacing. 
OBJECTS AND SUMMARY OF THE INVENTION 
The present invention has been made in consideration of the above-described 
problems and, therefore, has an object to solve great inconvenience as to 
manufacturing cost and packaging space, when it is so constituted that a 
tape drive speed based on a motor rotation frequency is detected and a 
predetermined pitch converting amount is automatically set in response to 
the amount of change of the tape drive speed. 
To this end, in accordance with an aspect of the present invention a sound 
reproducing apparatus is provided having pitch converting means capable of 
varying a playback drive speed of a recording medium from a rated drive 
speed and also capable of converting a pitch of a sound signal reproduced 
from the recording medium, the pitch converting means is so arranged that 
when the drive speed of the recording medium is varied from the rated 
drive speed, a pitch converting operation is carried out in response to a 
pitch control signal used to set a preselected pitch converting amount in 
accordance with the speed changing amount. A reproduced sound signal 
having substantially the same pitch as that found during rated drive speed 
can be output and the pitch control signal is produced as a signal 
corresponding to the drive speed of the recording medium by employing a 
drive signal of the motor that drives the recording medium during 
playback. 
Also, it is so arranged that the pitch control signal is produced as a 
signal corresponding to the drive speed of the recording medium by 
employing a rotation frequency control signal for controlling the rotation 
frequency, that is, the number of revolutions, of the motor providing the 
playback drive for the recording medium. 
It is noted that the drive signal of the motor corresponds to a signal 
related to the drive speed of the recording medium. Similarly, the 
rotation frequency control signal used to control the rotation frequency, 
that is, the number of revolutions, of the motor corresponds to a signal 
related to the number of motor revolutions indicating the drive speed of 
recording medium. 
As a consequence, a DC voltage proportionally corresponding to, for 
instance, the drive speed of the recording medium can be obtained from 
these signals. If this voltage is utilized, then a pitch control signal 
can be produced to perform a control such that a predetermined pitch 
converting amount is automatically set in correspondence with the amount 
of change of the drive speed, even when there is no FG mechanism for 
detecting the drive speed of the recording medium.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
A first embodiment of the present invention provides a pitch control signal 
produced by using the drive signal of the motor that sets the playback 
drive speed of the recording medium, whereas a second embodiment of the 
present invention provides a pitch control signal generated by using the 
rotation frequency control signal used for controlling the rotation 
frequency of the motor that sets the playback drive speed of the recording 
medium. 
First, a cassette tape recording/reproducing apparatus, that is, a 
so-called tape recorder, incorporating the first embodiment will now be 
explained with reference to FIGS. 1 through 12. 
FIG. 2 is an overall perspective view of a tape recorder 1 in which 
reference numeral 2 denotes a cassette tape loading unit, reference 
numeral 3 shows a flat microphone, reference numeral 4 is a speaker, and 
reference numeral 5 indicates operation keys for performing various tape 
operations, such as playback, record, stop, fast forward, and rewind. 
Reference numeral 6 shows a volume control knob for controlling the volume 
of the sounds reproduced from the speaker 4. 
In this tape recorder 1 reference numeral 7 indicates a pitch converting 
mode key, reference numeral 8 shows a speed control knob corresponding to 
a manipulation of a variable resistor (not shown in FIG. 2) for varying 
the tape speed, and reference numeral 9 is a pitch control knob 
corresponding to a manipulation of a variable resistor (not shown in FIG. 
2) for manually controlling the pitch converting amount of the reproduced 
sound. 
Reference numeral 10 shows an external microphone connection jack and 
reference numeral 11 indicates a headphone output jack. 
In this tape recorder 1 a user turns the speed control knob 8 in a plus (+) 
direction during playback so that the sound recorded on the tape can be 
reproduced with an increased tape drive speed, whereas the user turns this 
speed control knob 8 in a minus (-) direction with a decreased tape drive 
speed. 
As to the pitch converting mode key 7, three setting positions are defined 
by sliding this mode key. More specifically, the off-condition, manual 
condition, and auto-condition are set as the mode operations by mode key 
7. 
Under the manual mode condition, the user turns the pitch control knob 9 in 
a plus (+) direction, thereby increasing the pitch of the reproduced 
sound, or in a minus (-) direction thereby decreasing the pitch of the 
reproduced sound. 
Furthermore, under the auto-condition, the reproduced sound is outputted at 
the pitch present when the tape is driven at the rated speed, regardless 
of the tape speed at this time. That is, normally when the speed control 
knob 8 is turned to increase/decrease the tape drive speed during 
playback, the frequency of the reproduced signal would be 
increased/decreased in accordance with the speed controls, however, in the 
case of this auto-mode, the pitch conversion is carried out on the 
original frequency by changing the frequencies of the reproduced signal in 
response to changes in the tape drive speeds, so that the reproduced sound 
is output as if under normal tape speed conditions. For example, when the 
tape speed control is increased in such a manner that the pitch of the 
reproduced sound is increased by five sounds, a pitch converting process 
is carried out so as to lower the pitch of the playback signal by five 
sounds. 
It should be noted that the pitch control knob 9 does not work under this 
auto-condition mode. 
When the pitch converting mode key 7 is brought into the off condition, no 
pitch converting processes for the manual/auto conditions described above 
will be carried out. 
FIG. 1 is a block diagram of the major internal elements of the tape 
recorder 1. Symbol "T" indicates a magnetic tape wound on a pair of reels 
and stored in a tape cassette (not shown). In the tape recorder 1 of this 
embodiment, when the cassette tape is loaded in the cassette tape loading 
unit 2 and either the recording or reproducing operation is performed, the 
magnetic head 21 abuts the magnetic tape T to record/reproduce the audio 
signals. 
Reference numeral 22a indicates a capstan and reference numeral 22b a pinch 
roller, and both the capstan 22a and the pinch roller 22b rotate with the 
magnetic tape T sandwiched therebetween, so that the magnetic tape T is 
driven at a predetermined speed in response to the rotation speed of the 
capstan 22a. 
The rotation of the capstan 22a is performed by a motor 23, such as a 
3-phase brushless motor. Under control of a servo circuit 25, 3-phase 
drive signals (U,V,W) from a motor drive unit 24 are supplied to the motor 
23, so that the motor 23 is rotated at a preselected rotation speed. The 
servo circuit 25 controls the output of the motor drive unit 24 in 
response to a servo reference signal Esv. 
The servo reference signal Esv is produced by a servo reference signal 
producing unit 26 in accordance with the operation of the speed control 
knob 8. In other words, when the speed control knob 8 is set to an 
intermediate position, such as the position indicated by "N" in FIG. 2, 
the variable resistor (not shown) whose resistance value is varied by the 
speed control knob 8 has an intermediate resistance value within its 
resistance range, so that a servo reference signal Esv is obtained by 
which the rotation frequency of the motor 23 provides a tape drive speed 
that is the rated drive speed. When the speed control knob 8 is turned in 
the plus direction, a servo reference signal Esv is produced so that the 
rotation frequency of the motor 23 is increased in response to this 
turning angle and the tape drive speed increases. Conversely, when the 
speed control knob 8 is turned in the minus direction, a servo reference 
signal. Esv is outputted by which the rotation frequency of the motor 23 
is slowed in response to this turning angle and the tape speed decreases. 
A further description about this servo reference signal Esv will be 
provided in connection with the description of the second embodiment. This 
servo reference signal Esv corresponds to an output signal from a 
resistance-capacitance (RC) time-constant circuit in which the output 
signal is obtained by changing the charging voltage of the capacitor in 
accordance with the resistance value of the variable resistor in response 
to the manipulation of the speed control knob 8. In response to the 
frequency of this output represented by the servo reference signal Esv, 
the servo circuit 25 performs the servo operation. 
In the audio signal recording system, either the sound signal input from 
the microphone 3 or the sound signal derived from an external microphone 
connected to the external microphone jack 10 is selected by a switch 12, 
and the input signal is amplified by an amplifier 27, so that an amplified 
sound signal is supplied to a recording processing unit 28. Then, an audio 
signal to which the record equalizing process and the level controlling 
process have been performed in the recording process unit 28, is supplied 
via an Roterminal of the switch 29 to the magnetic head 21 and is recorded 
onto the magnetic tape T being driven at the rated speed. 
During playback the signal read from the magnetic tape T by the magnetic 
head 21 is supplied via a P-terminal of the switch 29 to a reproducing 
processing unit 30 in which playback equalization processing and the like 
are carried out. 
An audio signal output from the reproducing processing unit 30 is converted 
into a digital audio signal by an A/D converter 31, and the digital audio 
signal is fed to a pitch converting unit 32 constructed, for instance, as 
a digital signal processor (DSP). 
The pitch converting unit 32 performs the process for increasing/decreasing 
the pitch with respect to the entered digital audio signal in response to 
a pitch conversion control signal SPT, thereby outputting the 
pitch-converted audio signal. 
The output signal of the pitch converting unit 32 is returned to an analog 
signal by a D/A converter 33. Then, after level control has been executed 
by a sound volume control 34 that is variable by the volume control knob 
6, this analog signal is amplified to a predetermined level by an output 
amplifier 35 and is output as sounds or voice from the loudspeaker 4. 
Otherwise, this analog signal is supplied to a headphone output jack 11 to 
be output as sounds or voice over a headphone connected to this headphone 
output jack 11. 
In the pitch converting unit 32, the input digital audio signal from the 
A/D converter 31 is written into a RAM and is read out therefrom in a 
different manner from the writing manner, so as to realize the pitch or 
frequency conversion. This pitch converting operation will now be 
explained. 
Assuming that the sampling frequency of the A/D converter 31 is 16 Khz, the 
data for every 1/16,000 seconds (62.5 microseconds) are sequentially 
written into the RAM (not shown in FIG. 1) of the pitch converting unit 
32. When the data are read out from the RAM in the order of the data 
writing operation for every 1/16,000 seconds and sequentially output, the 
same waveform as that of the input signal to the A/D converter 31 can be 
reproduced at the output signal from the D/A converter 33. Thus, no pitch 
conversion is carried out. 
On the other hand, when pitch conversion is to be carried out, the data 
reading method for the RAM is changed as follows. First, in FIG. 9, there 
is shown a case in which the frequency of the audio is multiplied by 1/2, 
in other words, the sound pitch is lowered by one octave. Assuming now 
that the waveform of the input signal from the A/D converter 31 is a 
waveform such as shown at the lower portion of FIG. 9, the data that are 
sampled by the A/D converter 31 and then fed to the pitch converting unit 
32 are D1, D2, . . . Dn. Also, it is assumed that these data D1, D2, . . . 
Dn written into the RAM of the pitch converting unit 32 correspond to 
sound or audio data for 30 milliseconds. 
Here, when reading from the RAM, if the data are sequentially read twice 
for the first data D1, then a waveform as shown in the upper portion of 
FIG. 9 is produced from the data, D1 to Dc, for an initial half period of 
15 ms. That is, since such read data are supplied to the D/A converter 33, 
an audio signal waveform whose frequency is one half is produced, so that 
it implies that the pitch conversion to lower the sound by one octave is 
carried out. It should be understood that the data (Dc+1to Dn) for a 
subsequent half period of 15 ms are unnecessary in this case. 
Next, FIG. 10 represents the case in which the frequency is multiplied by 
two, so that the sound pitch is increased by one octave. Assuming now that 
the input signal waveform of the A/D converter 31 is a waveform which is 
the same as shown in the lower portion of FIG. 9, then the data that are 
entered into the pitch converting unit 32 and stored in the RAM are D1, 
D2, . . . , Dn. 
In this case, every second data are read from the head data of the entire 
data stored in the RAM. That is, the data are sequentially read from the 
RAM in the order of D1, D3, D5, D7 . . . , Dn, whereby a waveform shown in 
the upper portion of FIG. 10 is produced as indicated by solid-line arrows 
from the lower portion waveform to the upper portion waveform in. It 
should be understood that since the data stored in the RAM for a 30 ms 
period are read as every second data D1, D3, . . . , the resultant 
waveform for only a 15 ms period is produced. Accordingly, after the last 
data Dn has been read, the data from D3, D5, D7, . . . , Dn are again read 
in the same order indicated by the dotted-line arrows from the lower 
portion waveform to the upper portion waveform in FIG. 10. As a 
consequence, as shown in the upper portion of FIG. 10, a waveform having 
twice the pitch as the original signal is produced for a 30 ms period. 
Furthermore, when the pitch is converted into an intermediate condition 
between one-half pitch and two-times pitch, the RAM reading method is 
varied in accordance with this intermediate pitch converting amount. For 
instance, there is shown in FIG. 11 the case in which the sound is 
pitch-converted by -30%, which is approximately -3.5 tones. 
In this case, as to the data D1 to Dn held in the RAM, one piece of data is 
doubled and read out twice from this RAM for every three pieces of data. 
That is, the data are read in the sequence of D1, D2, D3, D3, D4, D5, D6, 
D6, . . . . Then, when the data DE has been read out, pitch-converted data 
corresponding to the 30 ms time length of the input data is produced, as 
illustrated in an upper portion waveform in FIG. 11. This pitch-converted 
data is D/A-converted to produce an audio signal whose pitch has been 
converted downwardly by approximately -3.5 tones. 
Similarly, in case of other pitch converting amounts, the RAM reading 
method is set in response to their pitch converting amounts for performing 
the proper pitch conversion. 
Referring back to FIG. 1, the pitch conversion control signal SPT for 
controlling the pitch converting amount in the pitch converting unit 32 is 
produced by pitch control signal generating units 36 and 52, and the 
output from one of these units is selected by a switch 38 and is supplied 
to the pitch converting unit 32. 
The switch 38 is switched by the pitch mode control key 7 operated by the 
user. When the slide position of the pitch mode key 7 is set to the manual 
mode position, the MN input terminal of this switch 38 is connected to the 
output. When the slide position of the pitch mode key 7 is set to the auto 
(AT) mode position, the AT input terminal is connected to the output. When 
the slide position of pitch mode control key 7 is set to the off mode 
position, the blank OF terminal is connected to the output. 
When the switch 38 is connected to the OF terminal, no pitch conversion 
control signal SPT is supplied to the pitch converting unit 32 and, 
therefore, no pitch conversion is carried out. 
When the switch 38 is connected to the MN terminal, the pitch conversion 
control signal SPT having a preselected potential in accordance with the 
resistance value of the variable resistor functioning in accordance the 
manipulation of the pitch control knob 9 is produced from the pitch 
control signal generating unit 36, and then is supplied to the pitch 
converting unit 32, so that the pitch converting process is performed in 
correspondence with the manipulation of the pitch control knob 9 by the 
user. 
When the switch 38 is connected to the AT terminal, the pitch converting 
process is carried out in the manner that the reproduced sound is output 
with a pitch corresponding to when the tape is driven at the rated speed 
regardless of the present tape speed. As a result, the pitch conversion 
control signal SPT having a predetermined potential is output from the 
pitch control signal generating unit 52 based on the present tape drive 
speed information, and then is supplied to the pitch converting unit 32. 
As a consequence, even when the tape speed is selected to be faster than 
the rated speed, or slower than the rated speed, easy-listening sounds 
having a normal tone and pitch can be reproduced. 
The relation among the pitch-converting amount, the frequency f.sub.0 at 
the rated drive speed at the rated drive speed, and the frequency f.sub.n 
after pitch conversion is shown by the following expression: 
EQU f.sub.n =2.sup.n/12 .times.f.sub.0 (1) 
where n=the pitch converting amount.times.2. 
The relationship in FIGS. 12 are derived from this expression. 
FIG. 12 shows a conversion table that is contained in the pitch converting 
unit 32, for example, which is shown in more detail in FIG. 13. Column (a) 
in FIG. 12 represents pitch conversion amounts related to the pitch 
conversion control signal SPT when the operation voltage VDD is set to 3.5 
V. In this example, 32-staged voltages are set with respect to this 
operation voltage VDD when set at 3.5 V, and the pitch control signal 
generating unit 52 supplies them to the pitch converting unit 32 as the 
pitch conversion control signal SPT. For example, as seen from column 
(b)v, in case of the pitch conversion control signal SPT=2.19 V to 2.08 V, 
no pitch conversion is carried out. In case of the pitch conversion 
control signal SPT when VDD=3.5 V, the pitch conversion is performed in 
order that the sound is increased by 6 tones (1 octave). In case of the 
pitch conversion control signal SPT when VDD=0.88 to 0.77 V, the pitch 
conversion is performed in order that the sound is decreased by 6 tones (1 
octave). 
Moreover, in case of the auto mode, as shown in column (e) of FIG. 12, the 
pitch conversion is performed in response to the change in the number of 
motor revolutions, that is, the tape drive speed. The pitch conversion 
amount of the reproduced audio signal caused by this change in the number 
of motor revolution (tape drive speed), corresponds to column (b) in FIG. 
12. 
Column (c) in FIG. 12 indicates the frequency changing rate with respect to 
the sound data when the pitch conversion amount is zero and to the various 
sound data for the other respective pitch conversion amounts. That is, the 
pitch change in the reproduced audio signal caused by the change in the 
tape drive speed is returned to the pitch of the reproduced audio signal 
during the rated drive speed, and the pitch converting process 
corresponding to the frequency changing rate shown in column (d) of FIG. 
12 is performed. 
In other words, when the auto mode is selected, the pitch control signal 
generating unit 52 may produce the pitch conversion control signal SPT 
which becomes the voltage value of column (a) in accordance with the 
number of motor revolutions shown in column (e). Accordingly, this tape 
recorder of FIG. 1 can produce a sound output having the normal pitch 
regardless of the tape drive speed. 
It should be noted in this case that the pitch control signal generating 
unit 52 requires a signal that linearly responds to the tape speed change, 
or the voltage proportionally varied in response to the tape speed change, 
as the tape drive speed information. 
To this end, both a pulse generating unit 50 and a frequency-to-voltage 
converting unit 51 are employed in this embodiment. 
The pulse generating unit 50 receives, for example, the U-phase signal 
waveform among the 3-phase (U,V,W) drive signals output from the motor 
drive unit 24 and generates a pulse in correspondence with the frequency 
of this U-phase waveform. In FIGS. 3(a), 3(b), 3(c), there are shown 
various operations of the pulse generating unit 50 during the tape drives 
at rated speed, high speed, and low speed, respectively. 
The pulse generating unit 50 includes a comparator (not shown) for 
comparing the U-phase drive signal with the reference voltage Vref10, and 
further includes a one-shot multivibrator (not shown) for outputting a 
pulse having a fixed pulse width (Wa) by using a rising edge of an output 
pulse from the comparator as a trigger. As apparent from FIGS. 3(a) to 
FIG. 3(c), frequency pulses in correspondence with the U-phase drive 
signal can be obtained as the output of the one-shot multivibrator. The 
output from this one-shot multivibrator corresponds to the pulse having a 
frequency determined in accordance with the tape drive speed. 
This output from the pulse generating unit 50 is converted in the f/v 
converting unit 51 into a voltage value proportional to the frequency 
using a converting characteristic such as shown in FIG. 4, and then the 
converted voltage signal is applied to the pitch control signal generating 
unit 52. In other words, a voltage value is applied to the pitch control 
signal generating unit 52 that is varied in proportion to the tape speed 
variation. Since this voltage signal is to control the above-described 
pitch converting process in the auto mode, a pitch conversion control 
signal SPT based on the values shown in FIG. 12 may be output. 
A pitch converting unit 32 is shown in more detail in FIG. 13 and has the 
table of FIG. 12 that represents the relation between S.sub.PT and the 
pitch converting amount stored in a read only memory (ROM) 90. The ROM 90 
receives the S.sub.PT signal and read-out amount from the ROM 90 is fed to 
a digital signal processor 91 that has associated with it a data memory 
(RAM) 92. The data memory 92 functions with the digital signal processor 
91 in the conventional fashion. The input sound data from the A/D 
converter 31 is fed as the input signal to the digital signal processor 91 
that produces the pitch converted sound data fed to the D/A converter 33 
in response to the pitch conversion amount from the table ROM 90. 
An example of the actual circuits corresponding to the pulse generating 
unit 50, the f/v converting unit 51, and the pitch control signal 
generating unit 52 is shown in FIG. 5. 
In FIG. 5, reference numeral 80 indicates a terminal at which the U-phase 
drive signal corresponding to the output from the motor drive unit 24 is 
applied. Reference numerals 81 to 87 show circuit units constructed of an 
IC chip in which reference numeral 81 is a one-shot multivibrator, 
reference numeral 82 shows a comparator unit, and reference numeral 83 
indicates an operational amplifier unit. Reference numeral 84 is an analog 
switch unit, reference numeral 85 shows an inverter, reference numeral 86 
indicates an EX-OR circuit, and reference numeral 87 indicates an 
operational amplifier unit. Reference numeral 88 denotes a terminal from 
which the pitch conversion control signal SPT is output, and this signal 
corresponds to the output from the pitch control signal generating unit 52 
of FIG. 1. 
The U-phase drive signal fed in at terminal 80 is supplied to a (-) input 
terminal of a comparator 82a employed in the comparator unit 82. A 
reference voltage Vref10 produced by sub-dividing the power source voltage 
Vcc by resistors R804 and R805 is applied to a (+) input terminal of this 
comparator 82a. 
As a consequence, as illustrated in FIGS. 3(a) to 3(c), the U-phase drive 
signal is compared with the reference voltage Vref10 in the comparator 
82a, so that a pulse corresponding to the frequency of the U-phase drive 
signal is output. 
An output from the comparator 82a is supplied as a trigger to the one-shot 
multivibrator 81. In the one-shot multivibrator 81, the rising portion of 
the output pulse from the comparator 82a is employed as the trigger, and a 
pulse having a pulse width "Wa" set by a resistor R801 and a capacitor 
C802 is output as shown in FIGS. 3(a) to 3(c). The output of the one-shot 
multivibrator 81 is supplied to a series circuit made up of a resistor 
R803 and a capacitor C805, which comprise the f/v converting unit 51, and 
is rectified. Here, a voltage appearing across the capacitor C805 becomes 
a DC voltage depending on the frequency of the output pulse from the 
one-shot multivibrator 81. That is, since the DC voltage appearing across 
the capacitor C805 is determined by the pulse width and the charged 
electron amount defined by a time period of this pulse, when the pulse 
period becomes short a high DC voltage is obtained, whereas when the pulse 
period becomes long a low DC voltage is obtained. Then, as the time period 
of the pulse output from the one-shot multivibrator 81 is determined by 
the waveform of the drive signal derived from the terminal 80, the voltage 
across the capacitor C805 becomes higher when the tape drive speed becomes 
fast. Conversely, the voltage across the capacitor C805 becomes lower when 
the tape drive speed becomes slow. Thus, the f/v conversion output having 
the characteristic as shown in FIG. 4, namely the DC voltage relative to 
the tape drive speed, can be obtained. 
In the circuit of FIG. 5, the pitch control signal generating unit 52 
produces the pitch conversion control signal SPT in response to the 
voltage across the capacitor C805. 
Then the pitch shift operation based on the pitch conversion controlling 
signal SPT in the pitch converting unit 32 is carried out as shown, in 
accordance with the values in the table of FIG. 12. 
Both of the relationship (V/sound) between the pitch conversion control 
signal SPT and the pitch converting amount of columns (a) and (b) of FIG. 
12, and the relationship (f/sound) between the pitch converting amount and 
the frequency changing rate for the pitch zero conversion of columns (b) 
and (c) of FIG. 12, are graphically indicated in FIG. 6. 
On the other hand, the relationship between the pitch conversion control 
signal SPT and the number of motor revolutions is graphically indicated by 
the solid line in FIG. 7. 
As apparent from FIG. 6, the pitch converting amount is constantly changed 
with respect to the voltage changes of the pitch conversion control signal 
SPT. In this case, considering now that a proper amount of pitch 
conversion is performed in accordance with the change in the tape drive 
speed, and the converted pitch is returned to substantially the same pitch 
achieved during the rated drive speed as the above-described auto-mode 
operation, it would be preferable that the number of motor revolutions 
utilized to detect the tape speed, and also the voltage value of the pitch 
conversion control signal SPT, are uniformly varied with regard to the 
shift in the rotation frequency from the normal rotation frequency (200 
rpm) during the rated speed. Nevertheless, the relationship between the 
change in the pitch conversion control signal SPT and the change in the 
number of motor revolutions is not uniform, as is apparent from FIG. 7. 
However, when observing the number of motor revolutions for the high-speed 
side and the low-speed side on the basis of the normal revolution number 
(2000 rpm) at the rated speed, it may be seen as indicated by the broken 
line of FIG. 7 that it is approximated by two straight lines. 
In other words, the pitch control signal generating unit 52 may generate 
the pitch conversion control signal SPT, as indicated by the broken line 
of FIG. 7, such that the pitch conversion control signal has the 
characteristics of two approximated straight lines whose inclinations are 
different from each other on the basis of that of the rated speed, from 
the output (see FIG. 4) derived from the f/V converting unit 51, which 
corresponds to the voltage value uniformly changed in response to the 
number of motor revolutions. 
It should be noted that since these are approximated straight lines, the 
frequency of the pitch-converted signal is not exactly coincident with the 
frequency of the signal produced during the rated speed drive. 
Nevertheless, there is no practical problem that these frequencies can not 
be approximated within the range of shifts of +0.5 tone to -0.5 tone. 
A circuit arrangement and operations of the pitch control signal generating 
unit 52 to achieve the above-described approximation will now be explained 
with reference to FIG. 5 and FIG. 8. As shown in FIG. 5, the output from 
the f/V converting unit 51, namely the voltage across the capacitor C805, 
is applied to the (-) input terminal of the operational amplifier 83a 
employed in the operational amplifier unit 83. A DC potential produced by 
subdividing the power source voltage Vcc by the variable resistor RV801 is 
also applied via a resistor to this (-) input terminal of the operational 
amplifier 83a. Another DC potential (Vref11) produced by subdividing the 
power source voltage Vcc by resistors R832 and R33 is applied to the (+) 
input terminal of the operational amplifier 83a. 
More specifically, a potential offset by a voltage derived from the output 
potential of the f/V converting unit 51 by the variable resistor RV801 is 
inputted to the (-) input terminal of the operational amplifier 83a, and 
then a difference voltage between this potential and the reference 
potential Vref11 is invert-output from the operational amplifier 83a. 
The output from the operational amplifier 83a is used as the (-) input of 
an operational amplifier 83b. From the operational amplifier 83b, the 
reference voltage Vref11 corresponding to the (+) input is invert-output 
as a reference with respect to the output of this operational amplifier 
83b. 
It should be noted that the variable resistor RV801 is controlled in the 
manner that the output of the operational amplifier 83a obtained under the 
rated rotation frequency is coincident with the reference potential 
Vref11, whereby the above-described offset is set. 
The characteristics concerning the above-explained operations are indicated 
as curves 1, 2, and 3 in FIG. 8. 
The output from the operational amplifier 83b is supplied to the respective 
(-) input terminals of operational amplifiers 83c and 83d. The operational 
amplifiers 83c and 83d are inverting amplifiers having respective (+) 
input terminals to which is applied the same reference voltage Vref11 as 
in the operational amplifier 83b. The gain of the operational amplifier 
83c is controlled by way of the variable resistor RV802, whereas the gain 
of the operational amplifier 83d is controlled by way of the variable 
resistor RV803. 
The reason why the output of the operational amplifier 83b is 
simultaneously inputted to both of the operational amplifiers 83c and 83d, 
and further why the gain controls of these operational amplifiers 83c and 
83d are separately executed by the variable resistors RV802 and RV803, is 
the requirement to produce such pitch conversion control signals SPT 
having different characteristics during the high-speed drive and the 
low-speed drive on the basis of the reference characteristic during rated 
speed, as indicated by the broken line of FIG. 7 described above. 
In other words, the respective characteristics of the output signals from 
the operational amplifiers 83c and 83d are represented by the dot/dash 
line 4 in FIG. 8 and the broken line 5 in FIG. 8. To this end, the gain 
controls are separately performed. Further, as indicated by a shaded 
portion 6, which is the output of analog switch unit 84, when the number 
of motor revolutions is at the low speed, the output 4 of the operational 
amplifier 83c is selected to be used as the output 6 of the analog switch 
unit 84. When the number of motor revolutions is at the high speed, the 
output 5 of the operational amplifier 83d is selected to be used as the 
output 6 of the analog switch unit 84. Accordingly, the signals having 
such different characteristics during the high speed and the low speed are 
obtained. Then, the pitch conversion control signal SPT shown at 7 is 
produced based on the output 6 of the analog switch unit 84. 
First, to discriminate the characteristic during the high speed from the 
characteristic during the low speed on the basis of the characteristic 
during the rated speed, the output of the operational amplifier 83b is 
supplied to the (-) input terminal of the comparator 82b. To the (+) input 
terminal of this comparator 82b, a reference voltage Vref14 is applied 
that is produced by subdividing the power source voltage Vcc by resistors 
R816 and R817 and is identical to the reference voltage Vref11 in the 
operational amplifier unit 83. 
Since the reference voltage Vref11 equal to the reference voltage Vref14 is 
coincident with the output potentials of the operational amplifiers 83a 
and 83b when the tape is driven at the rated speed, since variable 
resistor RV801 is controlled so as to make it coincident with Vref11, the 
output from the comparator 82b for comparing the output 3 of the 
operational amplifier 83b with the reference voltage Vref14 will be an "L" 
level signal when the tape is driven at the low speed, whereas an "H" 
level signal is output when the tape is driven at the high speed. 
The output of this comparator 82b is converted by a transistor Q1 into "H", 
or "L" at the level of Vcc, which will be supplied to the analog switch 
unit 84 as a switching control signal for a switch 84b. The output of this 
transistor Q1 is inverted by an invertor 85 and the inverted signal is 
supplied as a switch control signal to the other switch 84a of the analog 
switch unit 84. As a consequence, any one of these switches 84a and 84b is 
turned ON in response to the output from the comparator 82b. The output of 
the operational amplifier 83c is supplied to the input terminal of the 
switch 84a, and the output of the operational amplifier 83d is supplied to 
the input terminal of the switch 84b. The outputs of the switches 84a and 
84b are connected to each other and are supplied to the operational 
amplifier unit 87. 
Accordingly, since the switch 84a and the switch 84b are controlled in 
response to the output from the comparator 82b, as described above, when 
the number of motor revolutions is slower than that of the rated speed, 
the output 4 of the operational amplifier 83c is selected to be used as 
the output 6 of the analog switch unit 84. When the number of motor 
rotations is faster than that of the rated speed, the output 5 of the 
operational amplifier 83d is selected to be used as the output 6 of the 
analog switch unit 84. 
The output selected by this analog switch unit 84 is amplified by an 
operational amplifier 87a whose gain is set by the variable resistor 
RV804, whereby a final output having the characteristic shown at 7 in FIG. 
8 is obtained. Specifically, the pitch conversion control signal SPT is 
obtained at the output terminal 88. Since this control signal is supplied 
to the pitch converting unit 32, the above-explained pitch converting 
operation in the auto mode is performed. 
As previously described, the variable resistor RV801 must be controlled so 
that the output of the operational amplifier 83b during the tape drive 
operation at the rated speed is coincident with the reference voltage 
Vref11, which is coincident with Vref14. Nevertheless, in practice it is 
very difficult to adjust the resistance value of this variable resistor 
RV801 during the manufacturing stage in a manner such that the pitch 
converting amount becomes precisely zero in case of the number of motor 
revolution (2000 rpm) at the rated drive speed. 
More specifically, when the tape is driven at the rated speed, the number 
of motor revolutions at the rated drive speed cannot be continuously 
maintained, and there is some risk that this number of motor revolutions 
will be increased and/or decreased to some extent. 
Therefore, if the pitch control operation is canceled within a certain 
allowable range with regard to the rotation frequency at the rated drive 
speed, as shown in FIG. 8, then the allowable range for the adjusting 
value may be widened and the adjusting stage can become simplified. 
Thus, to set the above-mentioned cancellation range, the comparators 82c, 
82d, the EX-OR circuit 86, and the transistor Q2 are employed in the 
circuit of FIG. 5. Then, the output from the operational amplifier 87a 
functioning as the pitch conversion control signal SPT is also supplied to 
the (-) input terminals of the comparators 82c and 82d. The reference 
voltages Vref12 and Vref13 having different values from each other are 
supplied to the respective (+) input terminals of the comparators 82c and 
82d. As these reference voltages Vref12 and Vref13, the following 
potentials are set by adding and subtracting the voltage (V) to and from 
the voltage value VPTO during the rated speed. That is, this voltage 
corresponds to the range of the rotation frequency which may constitute a 
cancel range+.alpha.% and -.alpha.% that is desired to be set for the 
voltage value (VPTO) of the pitch conversion control signal SPT during the 
rated speed. The outputs of the comparators 82c and 82d are fed to the 
inputs of the EX-OR circuit 86, respectively. 
Assuming now that, for instance, the reference voltage Vref12 of the 
comparator 82c is VPTO+V .alpha. and the reference voltage Vref13 of the 
comparator 82 is VPTO-V .alpha., the logic outputs of the comparators 82c, 
82d and the EX-OR circuit 86 are set out in correspondence with the tape 
drive speeds as: 
______________________________________ 
comp. 82c H H H H 
comp. 82d L H H H 
EX-OR 86 L H H L 
______________________________________ 
That is, as the output of the EX-OR circuit 86, an "H" output is obtained 
when it is present within the range of canceling width for the rotation 
frequency at the rated speed+.alpha.% and -.alpha.%. 
As indicated in the above table and FIG. 5, the pitch converting operation 
by the pitch converting unit 32 is canceled by setting the pitch 
conversion control signal SPT to the ground-level potential, so that when 
the output of the EX-OR circuit 86 becomes "H", the pitch conversion 
control signal SPT may be set to the ground level. 
As a consequence, since the output of the EX-OR circuit 86 is applied to 
the base of the transistor Q2, when the output from the EX-OR circuit 86 
becomes "H", the transistor Q2 is turned ON to cause the potential of the 
terminal 88 to be set to the ground level. 
It should be noted that if the output of the operational amplifier 87a is 
directly connected to the terminal 88, then the output potential of the 
operational amplifier 87a fed to the comparators 82c and 82d is also 
lowered when the transistor Q2 is turned ON. Then, any adverse influence 
given to the comparators 82c and 82d may be eliminated by connecting the 
output of the operational amplifier 87a to the terminal 88 via a resistor 
R840 having a sufficiently smaller resistance than the input impedance of 
the terminal 88, which is the control input terminal of the pitch 
converting unit 32. 
As described above, in accordance with this embodiment, since the pitch 
conversion control signal is produced from the motor drive signal and the 
pitch converting process in the auto mode is executed, the previously used 
rotation frequency detecting mechanism, such as FG, is no longer required, 
and a further increase in the circuit scale and total number of components 
can be avoided. 
In the second embodiment of the present invention the pitch control signal 
is produced by employing a rotation frequency control signal for 
controlling the rotation frequency of the motor, which sets the tape drive 
speed, and this second embodiment is shown in FIG. 14. The same reference 
numerals shown in the first embodiment of FIG. 1 are employed to denote 
the same circuit elements in this drawing and explanations thereof are 
omitted. 
In this case, due to the auto-mode control, a signal must be provided to 
the pitch control signal generating unit 52 that is a voltage value 
proportional to the number of motor revolutions similar to that shown in 
FIG. 4. However, since the pulse generating unit 50 and the f/V converting 
unit 51, which were included in the FIG. 1 embodiment, are not employed in 
this embodiment, a signal that is a voltage value proportional to the 
number of motor revolutions is derived from the servo reference signal 
generating unit 26 under control of the speed control knob 8 and is 
applied to the pitch control signal generating unit 52. The 
frequency-voltage relation is shown in FIG. 15. 
FIG. 16 shows the pitch control signal generating unit 52 in which the 
servo reference signal is supplied directly to input terminal 80 from the 
servo reference signal generating unit 26. The construction of the pitch 
control signal generating unit 52 shown in FIG. 16 is exactly the same as 
that shown in FIG. 5, which differs from FIG. 16 in that the pulse 
generating unit 50 and f/v converting unit 51 are not shown in FIG. 16. 
First of all, the servo system and the servo reference signal generating 
unit 26 according to this second embodiment will be described. As the 
servo system of the second embodiment, the servo reference signal 
generating unit 26 generates an RC time constant in correspondence with 
the user manipulation of the speed control knob 8 and this time constant 
is supplied as the servo reference signal to the servo circuit 25, whereby 
the number of revolutions, or the rotation frequency, of the motor 23 is 
controlled. 
Operabilities in the servo reference signal generating unit can be improved 
by eliminating the user's sense of incongruity caused by differences 
between the manipulating amount of the speed control knob 8 and the amount 
the tape speed actually changes in the following manner. The variable 
resistor corresponding to the manipulation of the speed control knob 8 is 
not directly employed as the RC time constant circuit that varies the time 
constant, but the resistance value in the RC time constant circuit is 
employed as the fixed value and the charging voltage of this RC time 
constant circuit is varied in proportion to the manipulating amount of the 
speed control knob 8. As a result, a change in the resistance values of 
the variable resistor corresponding to the speed control knob 8 has a 
proportional relationship with a change in the rotational frequency of the 
motor 23. 
It will now be explained using FIGS. 17, 18, and 19(a)-19(c) why the 
recharging voltage for the RC time constant circuit varies in proportion 
to the manipulating amount of the speed control knob 8 in the servo signal 
generating unit 26. 
FIG. 17 is a schematic diagram used to explain operations of the servo 
circuit 25 based on the servo reference signal. It should be understood 
that although the circuit of this model is different from the circuit 
arrangement of the previous embodiment, a variable resistor VR100 
manipulated by the speed control knob 8 is directly utilized as an RC time 
constant setting means with respect to the RC time constant circuit 
constituting the servo reference signal generating unit. In other words, 
FIG. 17 shows a simple model in which the time constant controll is 
carried out by changing the resistance value without varying the charging 
voltage. 
In this case, an E-terminal of the servo circuit unit 25 is used as a 
charging voltage source. A charging voltage "E" derived from the 
E-terminal is used to charge a capacitor C3 series-connected to ground via 
a resistor R100 and the variable resistor VR100. Then, a voltage Vc across 
the capacitor C3 is connected as a servo reference signal ESV to an SAW 
terminal. The servo circuit 25 controls the motor drive unit 24 by using 
this servo reference signal ESV as a reference, whereby the motor M is 
driven. It should be noted that the variable resistor VR100 corresponds to 
the variable resistor whose slider is moved by the speed control knob 8. 
In other words, the RC time constant provided by the variable resistor 
VR100 and the capacitor C3 can be directly changed in response to the 
manipulation by the user. 
The operation of the servo circuit 25 that is connected corresponding to 
this embodiment and the model shown in FIG. 14 is explained with reference 
to FIG. 18. Although not shown in FIG. 17, a discharging transistor is 
connected to the SAW terminal within the servo circuit 25. As shown in 
FIG. 18, if the discharging transistor (not shown) is turned OFF at the 
same time that the power is started to be supplied to the V phase of the 
motor, the charging operation of the capacitor C3 is commenced. Then, when 
the voltage Vc across the capacitor C3 reaches a constant potential 
(VCOMP), the discharging transistor functions so that the electrons 
charged into the capacitor C3 are discharged. Thereafter, when the supply 
of power to the U phase is commenced, the charging operation of the 
capacitor C3 is commenced, assuming that supply of power to motor coils is 
performed in sequence of U, V, W, U, . . . . 
As a result of such operations, sawtooth-shaped waveforms as shown at (b) 
in FIG. 18 are supplied as the servo reference signal ESV to the servo 
circuit 25. Here, time T1 is determined based on the CR charging time 
constant, and is expressed as: 
EQU T.sub.1 =-CR.multidot.ln(1-Vcomp/E) (2) 
On the other hand, assuming that time T2 of FIG. 18 is equal to one half of 
the time T1 (T2=T1/2), a frequency F1(Hz) of the sawtooth waveform shown 
at (b) in FIG. 18 is expressed as: 
EQU F.sub.1 =1/(1.5T.sub.1) (3) 
In a servo circuit of this unit, the number of motor revolutions is 
controlled in response to this frequency F1. 
Now, in the circuit of FIG. 17, when a change rate for the number of motor 
revolutions under the following conditions is calculated, it is obtained 
in accordance with the chart illustrated in FIG. 19. That is, the 
conditions assume that the variable resistor RV100 is 100 Kohms, the 
resistor R100 is 10 Kohms, the capacitor C100 is 0.1 microfarad, and the 
charging voltage E is 1.5 V, and further the comparison reference voltage 
VCOMP is 0.6 V, a change in the frequency F1 with respect to a change in 
the variable resistor RV100 is calculated, and furthermore when the 
frequency F1 at 50% of the moving amount of the variable resistor RV100, 
that is, the midpoint of the moving range in the speed control operation, 
is employed as the reference (100%), the above-described changing rate for 
the motor rotation frequency is obtained. 
The relationship between the volume moving amount (operation amount) and 
the changing range for the motor rotation frequency is graphically shown 
in FIG. 19(b). As apparent from this graphic representation of FIG. 19(b), 
the change in the motor rotation frequencies is not uniform with respect 
to the moving amount of the variable resistor RV100. This implies that 
when the variable resistor RV100 has the B-characteristic curve where the 
resistance value thereof is linearly changed with regard to the rotation 
angles of the speed control knob 8, the number of motor revolutions is not 
varied linearly in response to the manipulation amount of this variable 
resistor by the user. For example, referring to FIG. 19(b), the number of 
motor revolutions is rapidly changed over the range where the manipulating 
amount of the variable resistor is from 0% to 20%, whereas the number of 
motor revolutions is not so greatly changed in the range where the 
manipulating amount is from 50% to 100%. As a consequence, the user feels 
a sense of incongruity as to the relationship between the manipulating 
amount and the change in the number of motor revolutions in actual use, 
and sometimes the user cannot easily control the number of motor 
revolutions to the desirable value. 
Thus, in accordance with this embodiment, in the servo reference signal 
generating unit 26, the charging voltage is varied in response to the 
manipulation of the speed control knob 8, and this charging voltage is 
applied to the RC time constant circuit. Then, this RC time constant 
circuit is connected to the servo circuit 25, which is the servo circuit 
for performing the operations as explained with reference to FIGS. 17 and 
18, so that the servo reference signal ESV having the sawtooth-shaped 
signal waveform shown in FIG. 18 is generated by the 
recharging/discharging operations. Then, the servo circuit 25 controls the 
rotation frequency of the motor 23 in response to the frequency F1 of this 
servo reference signal ESV. 
With this circuit arrangement, the change in the resistance values of the 
variable resistor of the speed control knob 8 can have a proportional 
relationship with the change in the rotation frequencies of the motor 
means, see FIG. 20(b), whereby the user's sense of incongruity in 
operation that occurs based on the difference between the manipulating 
amount of the speed control knob 8 and the actual amount of the change in 
tape drive speed can be eliminated, thereby improving the overall 
operability of the system. 
FIG. 21 is a circuit diagram of the servo reference signal generating 
circuit 26 according to this embodiment, in which the charging voltage 
applied to the RC time constant circuit is varied in correspondence with 
the manipulation amount of the speed control knob 8. In FIG. 21, RV4 is a 
variable resistor that is operated by the speed control knob 8, and the 
resistance value of this variable resistor is varied in response to the 
rotary operation of the speed control knob 8. In other words, the servo 
reference signal ESV for controlling the speed is produced in accordance 
with the resistance value of the variable resistor RV4, and this servo 
reference signal is output from the servo reference signal generating 
circuit 26 and fed to the servo circuit 25. 
Reference numeral 40 shows a voltage regulator, reference numeral 41 
indicates a buffer containing amplifiers 41a and 41b, and reference 
numeral 42 denotes an adder having an amplifier 42a. 
The power source voltage Vcc is applied to the input terminal of the 
voltage regulator 40. A voltage V1 appearing between the output terminal 
of the voltage regulator 40 and the ground terminal is set by a resistor 
R10 and a capacitor C1 and is used as a fixed voltage output. The voltage 
value of the fixed output voltage is adjustable by way of a variable 
resistor RV2. The output voltage V1 of the voltage regulator 40 is 
subdivided by a variable resistor RV4, and then the subdivided voltage is 
entered via a resistor R1 to the amplifier 41b of the buffer 41. The power 
source voltage Vcc is subdivided by the variable resistor RV1 and the 
subdivided voltage is applied to the amplifier 41a of the buffer 41. That 
is, a DC potential V.sub.A adjusted by the variable resistor RV4 is 
produced as the output of the amplifier 41b, whereas another DC potential 
V.sub.B adjusted by the variable resistor RV1 is produced as the output of 
the amplifier 41a. It should be noted that for the actual value of this DC 
potential V.sub.A, an arbitrary value can be obtained by the variable 
resistor RV2. The DC potentials V.sub.A and V.sub.B are applied via 
resistors R3 and R4 to the inverting input terminal of the adder amplifier 
42a of the adder 42. A voltage Vref2 set by resistors R9 and R8 is applied 
to the non-inverting input terminal of the adder amplifier 42a. 
The output voltage Vout of this adder amplifier 42a can be expressed as: 
EQU V.sub.out =V.sub.ref2 +[(V.sub.ref2 -V.sub.A)+(V.sub.ref2 -V.sub.B)](4) 
This output voltage Vout becomes the charging voltage E that is applied to 
the time constant circuit constructed of resistor R11 and capacitor C3. As 
previously explained in relation to FIGS. 14 and 15, the voltage across 
the capacitor C3 to which the charging operation and the discharging 
operation are performed, is applied to the SAW terminal of the servo 
circuit 25. The situation may be conceived in which there is no variable 
resistor RV3 parallel-connected between the center tap CT of the variable 
resistor RV4 and the hot side thereof in FIG. 21. In which case, as the DC 
potential V.sub.A, such potentials between 0V and the potential V1 appear 
which is proportional to the moving amount of the variable resistor RV4, 
that is, the rotation angle of the speed control knob 8. 
From the above-described equation (4), the following equation (5) may be 
induced. 
EQU V.sub.out =3.multidot.V.sub.ref2 -V.sub.B -V.sub.A (5) 
Since (3 Vref2-VB) contained in equation (5) is a constant that is not 
influenced by the DC potential V.sub.A, the output voltage Vout may be 
varied from (3Vref2-V.sub.B) to (3Vref2-V.sub.B -V1) by changing the DC 
potential V.sub.A between 0V and the potential V1. 
As previously explained, since the DC potential V.sub.A corresponds to a 
voltage produced by subdividing the voltage V1 by using the variable 
resistor RV4, when a variable resistor having the B-characteristic curve 
is employed as the variable resistor RV4, a voltage is obtained that is 
proportional to the moving amount of the variable resistor RV4 as the DC 
potential V.sub.A. As a result, a voltage proportional to the moving 
amount of the variable resistor RV4 can be obtained as the output voltage 
Vout, which is the charging voltage E. 
When the voltage waveform across the capacitor C in the RC time constant 
circuit is applied as the servo reference signal ESV to the servo circuit 
25 while the charging voltage E is varied in a proportional fashion in 
correspondence with the manipulation amount, a proportional relationship 
may be established between the manipulating angle of speed control knob 8 
and the changing rate for the rotation frequency of the motor 23, and this 
relationship is illustrated in FIGS. 20(a) and 20(b). 
For instance, it is assumed that in the above equation (1) to obtain the 
charging period T1 of the time constant signal corresponding to the servo 
reference signal, the resistance value of the resistor R is fixed (100 
Kohms) and the charging voltage E is changed from 0.5 V to 2.5 V in 
correspondence with the moving amount of the variable resistor RV4. 
Further, assuming that C=0.1 microfarads and the comparing reference 
voltage VCOMP=0.4 V, a change in the frequencies F1 is calculated by way 
of equations (1) and (2) with respect to a change in the charging voltages 
E. In addition, when the changing rate for the number of motor revolutions 
is calculated under the condition that the frequency F1 obtained when the 
charging voltage E=1.5 V is recognized as a reference (100%), the 
resultant changing rate is obtained as shown by the table in FIG. 20(a). A 
relationship between the manipulating amount of the variable resistor RV4 
and the changing rate for the number of motor revolution is graphically 
represented in FIG. 20(b). 
In other words, a linear characteristic as shown in FIG. 20(b) can be 
obtained as the characteristic about the changing range for the number of 
motor revolutions with respect to the manipulation of the speed control 
knob 8 in this embodiment, so that the operability is easily grasped by 
the user. 
The above-described explanation has been made based on the assumption that 
the variable resistor RV3 is not present. Now, the presence and function 
of the variable resistor RV3 will be described. 
Typically, at the time the tape recorder is manufactured and when the tape 
drive speed can be controlled by the user, as described above, it is 
preferable that when the speed control knob 8 is located at the center 
position, that is, position "N" in FIG. 2, the rated tape drive speed is 
normally set, and further the tape drive speed may be doubled along the 
direction toward the high-drive speed, taking account of the actual 
operation modes. It is not necessarily required, however, that the tape 
drive speed be multiplied by -2 along the direction toward the low-speed 
drive. For example, when the rated speed is selected to be 100%, it is 
sufficient to vary the tape drive speed up to approximately 70%. Moreover, 
the speed setting operation may sometimes provide easy manipulations by 
the user of the tape recorder. 
In other words, there are some possibilities in which the speed changing 
amount that is achieved when the speed control knob 8 is turned to the (+) 
side is greater than that achieved when the speed control knob 8 is turned 
to the (-) side. In this case, for instance, the characteristic as 
indicated by a solid line of FIG. 20(c) is set. 
In case of the characteristic shown by the solid line shown in FIG. 20(c), 
the rated speed in which the changing rate for the number of revolutions 
is set to 100% can be obtained at the position "N" of 50% of the moving 
amount, and approximately a 2.times.speed higher than the rated speed can 
be achieved at the position (+) of 0% of the moving amount. On the other 
hand, approximately 70% speed (30% reduced speed) lower than the rated 
speed can be achieved at the position (-) of the speed control moving 
amount. 
Assuming now that as described above no variable resistor RV3 is employed, 
the changing rate for the rotation frequency is variable between 
approximately 70% to 20% in response to the manipulation of the variable 
resistor RV4, and also the tape drive speed is controlled in accordance 
with this manipulation, so that a characteristic such as shown by a 
dot/dash line in FIG. 20(c) results. 
In this case, when the speed control knob 8 is located at the position "N" 
of 50% of the speed control moving amount, the tape drive speed is brought 
into a faster drive speed than the rated speed. 
Thus, the achieve the characteristic indicated by the solid line of FIG. 
20(c), the voltage V.sub.A at the position "N" is required to be 
increased. To this end, a variable resistor RV3 shown in FIG. 14 is 
parallel connected between the center tap CT of the variable resistor RV4 
and the hot side thereof. 
As a result, as shown in the circuit of FIG. 22, the variable resistor RV4 
is divided by the center tap CT into resistors RV4-1 and RV4-2 
(RV4-1=RV4-2). A voltage appearing at the center tap CT is equal to a 
voltage subdivided by the combined resistance value of the variable 
resistor RV3 and the resistor RV4-2, and the resistance value of the 
resistor RV4-1. 
Here, since RV4-1=RV4-2, the resistance value of the combined resistor 
established between the resistance value of the variable resistor RV3 and 
the resistance value of the resistor RV4-2 becomes lower than the 
resistance value of the resistor RV4-1, so that the voltage appearing at 
the center tap position can be increased. At this time, it is, of course, 
possible to control the voltage changing amount by the variable resistor 
RV3. 
Then, since the center tap position corresponds to the position "N" of the 
speed control knob 8, the characteristic as indicated by a solid line of 
FIG. 20(c) can be obtained. 
It should be understood that even when the variable resistor RV3 is 
employed, as explained above, the linearity of the DC potential V.sub.A 
with regard to the moving amount of the variable resistor RV4 caused by 
manipulation of speed control knob 8 can be maintained. 
When, for instance, the variable resistor RV4 is manipulated toward the 
ground side rather than the center tap CT side, the circuit of FIG. 22 
becomes the circuit as shown in FIG. 23. The DC potential V.sub.A is equal 
to the voltage subdivided by a resistance value of a series connection 
between the combined resistance between the variable resistor RV3 and the 
resistor RV4-2, and the resistor RV4-1a, and also the resistor RV4-1b. 
Namely, the DC potential V.sub.A is equal to a voltage defined in 
accordance with the moving amount of the resistor RV4-1a. 
Also, when the variable resistor RV4 is manipulated on the side of the 
voltage V1 from the center tap CT, the circuit becomes the circuit shown 
in FIG. 24. The DC potential V.sub.A becomes a voltage obtained by 
subdividing the voltage V1 by the resistor RV4-2a and the resistor RV4-2b. 
Namely, the DC potential V.sub.A corresponds to the voltage in 
correspondence with the moving amount of the resistor RV4-2a. 
If the opposite characteristic to the above-described characteristic is 
desirably set, namely, the speed changing amount obtained when the speed 
changing knob 8 is turned to the (+) side is smaller than the speed 
changing amount obtained when the speed changing knob 8 is turned to the 
(-) side, then the variable resistor RV3 may be arranged in a parallel 
manner between the center tap CT of the variable resistor RV4 and the 
ground. Alternatively, a resistor having a fixed resistance value may be 
arranged instead of the variable resistor RV3. 
As previously described, in accordance with this embodiment, the tape drive 
speed is varied in a proportional form in response to the manipulation of 
the speed control knob 8. When the auto mode is selected as the pitch 
conversion mode, a preselected amount of pitch conversion is performed by 
the pitch converting unit 32 in response to the speed changing amount. 
Even when the tape speed is changed, in order that the reproduced sound 
with similar tones to those obtained during the rated tape drive speed can 
be obtained, the pitch control signal generating unit 52 derives from the 
servo reference signal generating unit 26, such a voltage value as 
represented by the signal having a characteristic shown in FIG. 4 which is 
changed in proportion to the changes in tape speeds as the tape drive 
speed information. In the servo reference signal generating unit 26 of 
FIG. 21, the signal linearly responding to the tape speed variation 
corresponds to the output voltage Vout. 
As this output voltage Vout is derived from the terminal 44 of FIG. 21, the 
present motor rotation frequency information, which is the tape drive 
speed information, can be obtained. As previously explained in relation to 
FIG. 12, the pitch control signal generating unit 37 which becomes the 
voltage value of column(a) is produced in response to the number of motor 
revolutions represented in column(e), so that the pitch converting process 
in the auto mode is executed. 
It should be noted that since the voltage value derived from the terminal 
44 corresponds to the output of the f/v conversion in the first 
embodiment, the circuit arrangement of the pitch control signal generating 
unit 52 may be made similar to that shown in FIG. 5 except for the circuit 
portion constituting pulse generating unit 50 and f/v converting unit 51 
in FIG. 5. It should also be noted that since the potential obtained from 
the output of the f/v converting unit 51 in the first embodiment is 
different from the potential produced from the output voltage Vout in the 
second embodiment, the gain of the operational amplifier employed in the 
pitch control signal generating unit 52 shown in FIG. 5 must be changed. 
In this embodiment, as described above, the rotation frequency detecting 
mechanism FG and the circuit portion are not required by utilizing the 
output voltage Vout of the servo reference signal generating unit 26, and 
furthermore, increases in the circuit scale and also the number and size 
of the circuit components can be suppressed. 
While the present invention has been described with regard to the tape 
recorders as the first and second embodiments, the sound reproducing 
apparatus according to the present invention may be applied to other 
various electronic appliances other than tape players, for example, DAT 
and disk players. 
Also, the actual circuit arrangements are not limited to those of the first 
and second embodiments, but may be modified. 
As previously described, the sound reproducing apparatus of the present 
invention is arranged by that the signal related to the motor rotation 
frequency, which is the drive signal of the motor, or the rotation 
frequency control signal for controlling the rotation frequency of the 
motor, which sets the reproducing drive signal of the recording medium, is 
employed to produce the pitch control signal. As a consequence, when it is 
so constructed that the pitch conversion is automatically performed at a 
preselected pitch converting amount in response to the changing amount of 
the reproduced drive speed, no mechanism for detecting the number of motor 
revolutions (reproducing drive speed) such as FG is required. Accordingly, 
there are various merits that total number of circuit components can be 
reduced, the package spacing can be reduced, and the manufacturing cost 
can be reduced.