JPS58218011A - Pcm sound recorder and reproducer possible for recording and reproducing signal of large amplitude - Google Patents

Abstract

PURPOSE:To extend the dynamic range without increasing the cost, by recording and reproducing a signal of large amplitude without distortion and increase in number of bits. CONSTITUTION:When the amplitude of an input signal 1 exceeds a prescribed value, a large input detecting circuit 2 outputs an output signal representing that the input signal exceeds a reference value. Then, switches 3, 4 are changed over, the input signal is brought to an automatic amplitude suppression circuit 5 to output the signal as a signal of normal level. The detecting signal is given from the circuit 2 to a control signal generating circuit 7 and the signal is combined into a data and recorded as the control signal. When the said control signal is given to the data at the reproduction, a signal processing circuit 11 applies the signal to an amplitide extending signal generating circuit 13 and an analog signal DA-converted with switches 14, 15 passes through an amplitude extending circuit 16 for being extended with the amplitude and becoming an output signal 17.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a PCM recording/playback device, and particularly to a PCM recording/playback device that prevents a sudden increase in distortion even when recording and playing back large inputs.

Recently, PCM recording and playback devices have been attracting attention, but they have the drawback that as the recording level is increased, clipping (increase in distortion) begins suddenly after a certain level is exceeded. The problem with this rapid increase in distortion is that it was not present in conventional analog tape recorders.

The reason for this is that an AD converter is used to convert an analog signal to a digital signal, but if an input that exceeds the dynamic range determined by the number of bits of this converter comes in, it will hard clip. In order to take advantage of the good SA ratio, which is the biggest feature of a certain O PCM recording and playback device, when recording with the input as high as possible, if a slightly large input comes in (this often happens when performing live recording etc.) ) It is very difficult to set the level when recording because the sound immediately becomes distorted.
○This was a very big drawback. ○The only way to improve this drawback is to increase the dynamic range by increasing the number of bits, and simply increasing the number of bits would be extremely costly and unrealistic. It loses its sexuality.

Therefore, the present invention provides a PCM recording and playback device that can expand the dynamic range without increasing cost by recording and playing back large amplitude signals without distortion without increasing the number of bits. The purpose is to

FIG. 1 is a block diagram of a recording system according to an embodiment of the present invention, and FIG. 2 is a block diagram of a reproduction system according to the same embodiment. M1
In the figure, when the recording input signal is at a normal level, it passes through switches 3 and 4, enters the AD converter 6, is AD converted, becomes a digital signal, and enters the signal processing circuit 8, where it is processed and sent to the recording medium i. , 'l□.

However, when the amplitude of the input signal 1 reaches a large level □ above a certain level (which normally would clip), the large input detection circuit 2 is activated. The large input detection circuit 2 compares the input signal with a constant reference voltage, and outputs an output signal indicating that the input signal is at a large level when the input signal exceeds the reference value. The output signal switches the switch 3 and the switch 4 so that the input signal passes through the automatic amplitude suppression circuit 5. The automatic amplitude suppression circuit 5 is, for example, an AGC circuit, which automatically suppresses the amplitude of a large amplitude signal, converts the signal into a normal level signal, and outputs the signal to the AD converter 6. At the same time, a detection signal is sent from the large input detection circuit 2 to the control signal generation circuit 7, becomes a control signal (for example, a signal to be input into a control block of the EI AJ format), is incorporated into data, and is recorded on the recording medium 9.

When recorded at a normal level, as shown in FIG. 2, the signal that is reproduced from the recording medium 10 and becomes a digital signal enters the signal processing circuit 11 and undergoes signal processing, and the DA
It enters the converter 12 and is DA converted to become an analog signal, and the switch 14 and switch]5 are left as they are! □ Passes through and becomes output signal 17.

However, if the signal processing circuit 11 receives a control signal indicating that a large signal has been input, it is applied to the amplitude expansion signal generation circuit 13,
The DA-converted analog signal is expanded in amplitude through an amplitude expansion circuit 16 and output as an output signal 17.
becomes. An expander can be used as the amplitude expansion circuit 16.

That is, in the present invention, a large input detection circuit 2,
Control signal generation circuit 7, automatic amplitude suppression circuit 5, switch 3
, switch 4, amplitude expansion signal generation circuit 13, amplitude expansion circuit 16, switch 14, and switch 15 are added to satisfy the expected characteristics.

In addition, as another example, the automatic amplitude suppression circuit 5 of FIG.
In place of switches 3 and 4, an amplifier capable of varying the amplification level such as a voltage controlled attenuator (VCA) is used, and similarly the amplitude expansion circuit 16 and switch 1 shown in FIG.
The same VCA can also be used in place of switch i5 and switch i5.

Figure 3 shows the input vs. distortion characteristic after recording and playback.In the present invention, the amplitude suppression and expansion circuit operates only when a large input is received, so the conventional distortion characteristic is curve A. On the other hand, the present invention has a curve B. That is, the distortion rate when the amplitude suppression/expansion circuit is not operating is the same as that of the conventional one, but in the area where the amplitude suppression/expansion circuit is active, curve A is completely clipped, whereas curve B of the present invention is completely clipped. It can be seen that since the distortion rate improves in the region 180, the dynamic range expands as a result.

Curve C in Figure 3(b) is the distortion rate characteristic of a conventional example using a three-line approximation circuit, but the key point is still the input level.)
Since distortion deteriorates rapidly when D is exceeded, it can be seen that there is room to improve the distortion rate at a large level by applying the present invention.

As described above, according to the present invention, it is possible to realize a PCM recording and playback device in which the dynamic range can be easily expanded, and in which deterioration of distortion is not perceived to be audible.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a recording system of a circuit according to an embodiment of the present invention, Fig. 2 is a block diagram of a playback system of a circuit according to an embodiment of the present invention, and Fig. 3 is an input vs. distortion diagram of a PCM recording/reproducing device. Curve A in Figure (a) is the conventional one, Curve B is the one using the circuit of the present invention, and Curve C in Figure (b) is the one using the three-line approximation circuit. This is the distortion rate characteristic of a conventional example. 2...°゛°°°° large input detection circuit, 3.4.14
．． 15...11. Switch, 5...
・・・・・・Automatic amplitude suppression circuit, 6 ・・・・・・・・・
AD converter, 7... Control signal generation circuit, 8, 11... Signal processing circuit,
9,1o... Recording medium, 12...
・・・・・・DA converter, 13・・・・・・・・・
・Amplitude expansion signal generation circuit, 16...
Amplitude expansion circuit.

Claims (1)

[Claims] A circuit that monitors the amplitude of a recording input signal and determines whether or not the amplitude of the recording input signal is above a predetermined certain level; a circuit that suppresses the amplitude when
The part that suppresses the amplitude in the recording input signal, the P
A PCM recording and reproducing device comprising a circuit that reads a CM recording signal and detects the presence or absence of the control signal, and a circuit that expands the amplitude of the read signal in response to the detection of the control signal.