JPH0518119B2 - - Google Patents

Abstract

PURPOSE:To eliminate the phase disorder of an acoustic signal generated by DPCM (differential pulse code modulation) at a concatenation point and to obtain a playback signal which provides good sensation of heating without any noise by marking data so that bracketing points of respective blocks which sections the acoustic signal are in phase when the acoustic signal is written in a memory. CONSTITUTION:A zero-cross detecting circuit 12 which inputs a peak detection signal (b) outputs a marking command signal (c) to a marking circuit 13 simultaneously with the input of the peak signal. When time-axis compression is carried out during a read of data from an RAM7, marks added to the encoded data are addressed to skip every other block of the data which is read out block by block. On the other hand, when time-axis expansion is performed, a bracketing point of the signal for every block which is obtained in time-axis conversion is given at the time of the peak of the acoustic signal and in phase. Therefore, acoustic signals in respective blocks are concatenated in phase and the signal reproduced by decoding has no large phase shift.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides DPCM (Differential Pulse Code)
Modulation (differential pulse coding modulation) coded acoustic signal processing equipment, especially DPCM that performs time axis conversion
The present invention relates to a marking circuit for signal block separation in a coded audio signal processing device.

Conventionally, acoustic signals such as musical tone signals and audio signals
PCM (Pulse Coding Modulation) encodes the signal and converts the time axis of the signal, allowing you to change the playback speed without changing the pitch of the playback sound, or change the playback speed to subtly change the pitch. It is.

When performing such time axis conversion, the PCM encoded signal is divided into blocks at predetermined intervals, and highly correlated parts and silent parts of the signals in each block are detected.In the case of compression, Several cycles of the block are deleted in strongly correlated parts or silent parts, while when expanding, several cycles of the strongly correlated parts are inserted.

However, in the time-base conversion of an audio signal using conventional PCM encoding, when the audio signal is divided into blocks, the audio signal is divided into blocks at predetermined time intervals, regardless of the phase of the audio signal. It was divided. Therefore, when reading signals from memory, blocks of signals with different phases are read out one after the other, and connections with different phases occur in the reproduced acoustic signal, causing noise. There was a problem that the hearing quality of the reproduced sound deteriorated.

The present invention was made to solve the above problem, and when writing an audio signal encoded by DPCM (Differential Pulse Code Modulation) into a memory, the phase of the cutting point of each block that divides the audio signal is By marking them so that they are the same, and eliminating phase disturbances at the connection points of the acoustic signals read out from memory block by block based on these marks, a good hearing experience without noise is achieved after time axis conversion processing. Performs time axis conversion that allows you to obtain the playback sound of
The object of the present invention is to provide a marking circuit for signal block separation in a DPCM encoded audio signal processing device.

For this purpose, the present invention has one feature that, in order to read the audio signal that is encoded data in the DPCM encoded audio signal processing device from the memory block by block, a block separation point is set when writing the DPCM encoded data to the memory. A marking circuit for marking blocks, which includes a peak detection circuit that detects the peak of an input acoustic signal waveform, and masks a peak detection signal output from the peak detection circuit for a preset time. a timer circuit; a zero-cross detection circuit that detects a zero-cross of the DPCM encoded data and outputs a marking command signal based on the zero-cross detection and the masked peak detection signal; DPCM to
A marking circuit for signal block division in a DPCM encoded audio signal processing apparatus, characterized in that the marking circuit for applying a mark for block division to the data when writing the encoded data; The invention provides that when the marking command signal is not output from the zero-cross detection circuit by the time a preset time elapses after the mask setting time of the timer circuit has elapsed, a signal is sent to the zero-cross detection circuit to forcibly output the marking command signal. The gist of the present invention is a marking circuit for signal block separation in a DPCM encoded audio signal processing apparatus, which is equipped with a second timer circuit that outputs a second timer circuit.

Embodiments of the present invention will be described below based on the drawings.

Figure 1 shows the encoding circuit of a DPCM encoded audio signal processing device that performs time axis conversion, and marks for dividing blocks when writing DPCM codes into memory.
In other words, marks are used as read symbols when compressing or decompressing a DPCM encoded signal from memory and reading it block by block in order to change the read speed of the DPCM encoded acoustic signal from memory and perform time axis conversion. This figure shows a marking circuit for separating signal blocks. 2 is input terminal 1
This is an input filter that performs filtering by inputting and filtering analog audio signals such as audio signals and musical tone signals input from an audio signal, and sets a band by removing frequency components and noise that are unnecessary for audio signal processing. 3 is a compressor that compresses the amplitude of the input signal sent from the input filter 2; it compresses the signal amplitude for noise reduction operation;
In the DPCM signal decoding circuit, the signal is amplified by an expander. 4 is compressor 3
This is a sample-and-hold circuit that samples analog audio signals sent from the timing controller 8, and instantaneous amplitude values of continuous audio signal waveforms are taken out as sample values at the time intervals of sampling pulses sent from the timing controller 8. Reference numeral 5 denotes an A/D converter that quantizes the signal sampled by the sample-and-hold circuit 4 and converts it into a binary code. A/A of differential encoding that takes the difference between the
It is a D converter. 6 is for sequentially storing the encoded audio signal data sent from the A/D converter 5 in a register provided in a read/write memory (RAM) 7 and having a storage capacity for several blocks of audio signals. This is a write latch that latches on the RAM.
When a write permission signal is sent to RAM 7, encoded data is sent to RAM 7 through the data bus.
Encoded data is sequentially written to designated addresses in RAM 7. On the other hand, when writing encoded data to RAM 7, for example, a mark is placed in the least significant bit (LSB) to specify the cutting point of the block read from RAM 7 when performing time axis conversion by signal compression or expansion. (for example, a code of logic "1"), the block division marking circuit that performs such an operation is constructed as follows. Reference numeral 11 is a peak detection circuit that inputs the analog audio signal from the compressor 3 and detects its peak, and uses charging and discharging of a capacitor to generate a pulse-like peak detection signal at the positive peak or negative peak of the audio signal. Output. 14 is a timer circuit which masks the peak detection signal outputted from the peak detection circuit 11 for a preset time and stops outputting the signal, and when the marking command signal outputted from the zero-cross detection circuit 12, which will be described later, rises. A high-level masking signal is repeatedly output to the peak detection circuit 11 for a predetermined masking time from the time. The zero cross detection circuit 12 is A/
Output from D converter 5 to writing latch 6
The information of the most significant bit (MSB) of the DPCM encoded signal, that is, the sign of the encoded data is checked, and the peak detection signal from the peak detection circuit 11 is inputted, and the DPCM encoded data is input at the same time as the peak detection signal is inputted. Zero crossing where the difference goes from negative to positive, that is, the difference “0” where the difference goes from negative to positive.
The marking circuit 13 is configured to output a pulsed marking command signal to the marking circuit 13 when the point is detected. Note that the reason why the zero cross detection is obtained almost simultaneously with the peak detection signal is because the encoded signal output from the A/D converter 5 is a differential signal.
Therefore, when the peak detection circuit 11 detects a positive peak of the analog acoustic signal, the peak is detected by the DPCM output from the A/D converter 5.
Since it appears as a zero cross transition from positive to negative in the encoded signal, the zero cross detection circuit 12
The zero crossing that changes from positive to negative is detected while checking the most significant bit. The marking circuit 13 receives the marking command signal output from the zero-cross detection circuit 12, and marks, for example, the least significant bit (LSB) of the encoded data output from the A/D converter 5, indicating the cutting point of the block. For example, it operates to assign a logic "1" sign. 15 is the second one that operates when there is no sound input.
This is a timer circuit, and if the silent input signal continues, that is, if the marking of the cutting point that specifies the block cannot be done for a long time as it takes to go around the memory, the memory for several blocks of registers in RAM 7 will be cut off. Encoded data representing a silent state is stored without markings indicating equinoxes. In that case, the mark indicating the cutting point is detected for decoding, and data is read from the position of that mark, so data indicating silence is ignored.
There is no continuity in the sound during playback, creating a sense of discomfort, and the signal is perceived to be delayed. In order to prevent such a phenomenon from occurring, if a marking command signal is not output from the zero-cross detection circuit 12 even after a predetermined period of time has elapsed from the end of the mask signal from the timer circuit 14, a high-level signal is sent to the zero-cross detection circuit 12. Accordingly, the marking command signal is forcibly output.

Next, first, the operation of the marking circuit for block separation when a sound signal is inputted will be explained with reference to the waveform diagram of FIG.

An acoustic signal such as a musical tone signal or a voice signal is input from an input terminal 1, passes through an input filter 2 to remove frequency components and noise unnecessary for signal processing, and is sent to a compressor 3. The compressor 3 compresses the amplitude of the audio signal for noise reduction, etc., and sends the amplitude-compressed analog audio signal to the DPCM encoding processing circuit.
First, the signal is input to the sample/hold circuit 4 and sampling is performed. Sampling is performed at time intervals of sampling pulses sent from the timing controller 8, and each amplitude value is held as a sample value. Sample/hold circuit 4
The signal sampled by
The difference between these signals is quantized and converted into a binary code. That is, here, the difference between the input signal and the predicted signal of the continuously input sampled signal is quantized, and the quantized signal data is encoded into a binary number. The encoded data of the audio signal converted into a DPCM code by the A/D converter 5 is then sent to a write latch 6, where it is latched by a latch signal supplied from a timing controller 8. Then, the encoded data latched by the write latch 6 is sequentially transferred to the RAM 7.
The data is written into the RAM 7 at a constant speed while being addressed based on an address signal supplied from a writing counter (not shown).

On the other hand, when the encoded data is sent from the A/D converter 5 to the write latch 6 and temporarily stored, a mark indicating the block division point of the signal is placed in the least significant bit of the encoded data at a predetermined point of the audio signal. It is given as follows at the peak position of .

That is, the analog acoustic signal a output from the compressor 3 is input to the peak detection circuit 11, and the negative peak of the acoustic signal a is detected using charging and discharging of the capacitor, and a peak detection signal b indicating the position of this peak is generated. is output from the peak detection circuit 11. At this time, the timer circuit 14 outputs a preset time after the previous marking signal c is output from the zero cross detection circuit 12, for example, the time T _M
Since the output signal d for masking the peak detection signal by the amount of time is output to the peak detection circuit 11, the peak detection during this period is canceled. Therefore, the approximate marking time interval, that is, the length of the block, is determined by the set time of the timer circuit 14. The zero-cross detection circuit 12 inputting such a peak detection signal b checks the most significant bit with a positive or negative sign of the encoded data latched in the write latch 6 simultaneously with the input of the peak signal b. , when detecting a zero crossing point where the positive/negative signal of each data changes from negative to positive, outputs a marking command signal c to the marking circuit 13. Then, in the marking circuit 13 to which the marking command signal c is input, a mark indicating the cutting point of the block is attached, for example, to the least significant bit of the encoded data latched in the write latch 6, with a code of logic "1". Ru.

In this way, the encoded data with marks indicating the block division points are stored in the RAM 7, and when read from there, time axis conversion is performed by signal compression and expansion. i.e. RAM
When compression of the time axis is performed when reading data from 7, an operation is performed in which a mark attached to encoded data is specified as an address and when data is read out block by block, some blocks are skipped and read out. On the other hand, when expanding the time axis, the same data block is read out multiple times based on mark information, and a new block is inserted. As described above, the cutting point is set at the peak of the acoustic signal and is a point of the same phase. Therefore, the audio signals of each block are connected with the same phase, and there is no large phase shift in the decoded and reproduced signal, so no connection noise or deterioration of hearing sensation occurs. figure,
It can produce good playback sound.

On the other hand, if the silent signal continues, the embodiment shown in FIG. 2 cannot detect a peak and cannot perform marking, which causes problems in time axis conversion processing.

Therefore, as shown in FIG. 3, when the silent acoustic signal _a1 is input, the second timer circuit 1
5, when a predetermined marking signal is not output from the zero cross detection circuit 12, the output signal e is detected as a zero cross after a preset delay time T _D from the falling edge of the mask signal _d1 output from the timer circuit 14. Output to circuit 12. The zero cross detection circuit 12, which has input the output signal e from the second timer circuit 15, unconditionally outputs the marking command signal _c1 to the marking circuit 13 at this time, and similarly to the above, the mark indicating the cutting point of the block is Added to part of encoded data.

In this way, marks are added at predetermined intervals to indicate the block cutting points even when there is no sound input, so that even when an acoustic signal with a sudden attack part is input after a period of silence, the reproduced sound It is possible to prevent the input signal from occurring with a large delay, and to follow the original input signal and make it rise.

As explained above, according to the marking circuit for signal block division of the DPCM encoded audio signal processing device that performs time axis conversion of the present invention, since the encoded data is marked at the peak position of the audio signal, Points of the same phase in the acoustic signal can be used as the cutting points of the blocks, and when reading the encoded data of the acoustic signal for each block from the memory for time axis conversion, compression and expansion are performed to separate each block. Even if the block is deleted or repeatedly inserted, the phase at the connection point of each block is not disturbed, and therefore noise generation and deterioration of hearing sensation can be prevented. Further, since marks can be added to the encoded data at predetermined time intervals even when a silent input signal is being input, problems such as delays in reproduced sound due to the absence of marks during a certain period when reading from the memory are not caused.

[Brief explanation of drawings]

The figure shows an embodiment of the present invention, and Figure 1 is a DPCM
A block diagram showing the encoding circuit of the encoded audio signal processing device and its marking circuit for signal block division, FIG. 2 is a waveform diagram of the audio signal and the output signal of each circuit, and FIG. FIG. 3 is an output signal waveform diagram of the circuit. 6...Latch for writing, 7...RAM (memory), 11...Peak detection circuit, 12...Zero cross detection circuit, 13...Marking circuit, 14...
...Timer circuit, 15...Second timer circuit.

Claims (1)

[Scope of Claims] 1. In order to read the audio signal that is encoded data in the DPCM encoded audio signal processing device from the memory block by block, marks of block division points are set when writing the DPCM encoded data to the memory. A marking circuit for dividing blocks,
A peak detection circuit that detects the peak of an input acoustic signal waveform, a timer circuit that masks the peak detection signal output from the peak detection circuit for a preset time, and a zero cross of the DPCM encoded data. and a zero-cross detection circuit that outputs a marking command signal based on the zero-cross detection and the peak detection signal after the masking, and when writing the DPCM encoded data to the memory by inputting the marking command signal;
1. A marking circuit for signal block division in a DPCM encoded audio signal processing apparatus, comprising a marking circuit for applying marks for block division to the data. 2. Marking for block division that marks the block division point when writing DPCM encoded data into memory in order to read the audio signal that is encoded data in the DPCM encoded audio signal processing device from the memory block by block. It is a circuit,
A peak detection circuit that detects the peak of an input acoustic signal waveform, a timer circuit that masks the peak detection signal output from the peak detection circuit for a preset time, and a zero cross of the DPCM encoded data. and a zero-cross detection circuit that outputs a marking command signal based on the zero-cross detection and the peak detection signal after the masking, and when writing the DPCM encoded data to the memory by inputting the marking command signal;
When a marking command signal is not outputted from the zero-cross detection circuit until a preset time elapses after the mask setting time of the marking circuit and the timer circuit has elapsed, which applies a mark for dividing the block to the data, A marking circuit for signal block separation of a DPCM encoded acoustic signal processing device, comprising a second timer circuit that outputs a command signal to a zero-cross detection circuit to forcibly output a marking command signal.