JP2002111498A - Digital attenuatig circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital attenuating circuit given measures to prevent a substantial occurrences of a reduction in accuracy generated by performing an attenuating process and a reduction in sound quality due to a decrease of dynamic-range when attenuated digital output signal is outputted through an attenuating digital process. SOLUTION: In the circuit, a digital attenuator 5 to perform a digital attenuating process with increasing a data length (16 bits) of a digital signal from a digital signal processing circuit 1 or an A/D conversion circuit 2 selected by an operation of a switching circuit 3 to multiply a predetermined factor to the digital signal is equipped. Furthermore, a wave processing circuit 6 to generate the attenuated digital output signal having an equivalent data length to an original length with performing a rounding process such as a noise shaving process or dither process to bits of a lower part than that of a signal responding to original bits of an output from the attenuator 5 is equipped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital attenuator circuit, and more particularly, to an attenuated digital output signal obtained by performing an attenuated digital process by multiplying a code sequence of a digital input signal composed of PCM data having a predetermined data length by a predetermined coefficient. The present invention relates to improvement of a digital attenuator circuit that outputs a signal.

[0002]

2. Description of the Related Art A digital attenuator circuit is used by being inserted in the middle of a digital signal transmission system. When used in an input stage of a digital signal recording device, a CD-R or CD is used as a recording medium of the recording device. -RW, DAT, M
D, DVD-R, DVD-RW, DVD-RAM, hard disk, semiconductor memory, etc. exist, and when digital recording is performed using these recording media, the digital input signal is recorded at the same volume level. Instead, recording is often performed with the recording volume adjusted.

[0003] When a digital attenuator circuit is inserted into the input stage of a recording device, the volume of each sound source is adjusted when a plurality of sound sources are edited and dubbed, a single recording volume is adjusted, a stereo balance is adjusted. Fade-in processing,
It is used for fade-out processing, cross-fade processing, and the like.

[0004] When the recording volume adjustment is analogously attenuated, the digital input signal is temporarily converted to an analog signal using a D / A conversion circuit, and after the volume is adjusted, the D / A is adjusted. Since it is necessary to restore the digital signal by performing conversion (A / D conversion) reverse to the conversion, the configuration becomes complicated and signal deterioration often occurs. The use of a digital attenuator circuit for adjustment has become mainstream.

A digital attenuator circuit has, for example, 16
An attenuated digital signal is obtained by multiplying a code sequence of a digital input signal composed of PCM data having a predetermined data length of 24 bits or 24 bits by a predetermined coefficient, and the PCM data is converted to “0” and 0 dB corresponding to −∞. Corresponding "1"
And outputs an attenuated digital output signal.

[0006]

A conventional digital attenuator circuit uses a digital code of a digital input signal of -∞.
The attenuated digital output signal is obtained by arbitrarily multiplying a coefficient of “1” corresponding to 0 dB and “1” corresponding to 0 dB, for example, in the case of 16-bit data, for example, −12 dB. When attenuating, the lower two bits of data are truncated.
The accuracy simply drops to 14-bit information. In other words, the inherent 16-bit dynamic range is reduced to 14 bits.

These facts can be applied not only to the case of applying -12 dB of attenuation but also to the case of applying attenuation. As the amount of attenuation is larger, a part of the information amount of voice is lost. As a result, the reproduction quality is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide an attenuating digital output signal which is obtained by multiplying a code string of a digital input signal composed of PCM data having a predetermined data length by a predetermined coefficient to output an attenuated digital output signal. It is an object of the present invention to provide a digital attenuator circuit in which measures are taken so that the audio quality is not substantially degraded due to a decrease in accuracy or a decrease in dynamic range caused by performing the above.

[0009]

In order to solve the above-mentioned problems, a digital attenuator circuit according to the present invention employs the following characteristic configuration.

(1) In a digital attenuator circuit for performing attenuated digital processing by multiplying a code sequence of a digital input signal composed of PCM data having a predetermined data length by a predetermined coefficient to output an attenuated digital output signal, A first signal processing means for generating an expanded digital signal having an increased data length and subjecting the expanded digital signal to digital attenuation processing by multiplying the expanded digital signal by a predetermined coefficient; and an output of the first signal processing means. The lower bits of the expanded digital signal corresponding to the least significant bit of the digital input signal, by performing rounding processing such as noise shaving processing and dither processing,
A digital attenuator circuit comprising: a second signal processing unit that performs a waveform process so as to generate an attenuated digital output signal having a data length equivalent to the data length of the digital input signal.

(2) A digital attenuator circuit in which the digital input signal input to the first signal processing means of (1) is constituted by data obtained by linearly A / D converting an analog sound source.

(3) A digital attenuator circuit comprising a digital input signal inputted to the first signal processing means of the above (1), which is constituted by data obtained by A / D converting an analog sound source by using a predetermined compression means.

(4) A digital attenuator circuit configured so that the rounding process performed by the second signal processing means of (1) is performed in a range of 3 to 4 bits lower than the predetermined data length.

(5) A digital attenuator circuit configured so that the rounding processing performed by the second signal processing means of (1) is performed in a digital code area corresponding to a voice band of 10 kHz or more, which has a low audibility.

(6) The circuit comprising the first signal processing means and the second signal processing means according to any one of (1) to (5) is used by being inserted in the middle of a digital signal transmission system. Digital attenuator circuit that can be used.

(7) A digital attenuator circuit wherein the circuit comprising the first signal processing means and the second signal processing means of (6) is used in an input stage of a digital signal recording device.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, the circuit configuration will be described with reference to FIG. This embodiment is an example in which the present invention is applied to a case where either a digital input or an analog input is selected, and the selected input is subjected to an attenuation process to obtain a digital output, and the data format standard of S / P-DIF is used. Is converted into a 16-bit PCM signal by the digital signal processing circuit 1 and supplied to one terminal of the switch circuit 3.

A digital signal obtained by converting an analog input into a 16-bit PCM signal by the A / D conversion circuit 2 is supplied to the other terminal of the switch circuit 3.

PC of digital input or analog input system selected by operating switch circuit 3
The M16-bit signal is input to the digital attenuator circuit 4.

The digital attenuator circuit 4 is configured by connecting first signal processing means and second signal processing means in series. The first signal processing means is constituted by a digital attenuator 5, generates an expanded digital signal in which the data length (16 bits) of the digital input signal selected by the switch circuit 3 is increased to 32 bits, and generates the expanded digital signal. Digital attenuation processing is performed by multiplying the signal by a predetermined coefficient.

The second signal processing means is constituted by a waveform processing circuit 6 and converts a lower bit of the expanded digital signal corresponding to the least significant bit of the digital input signal, which is included in the output of the digital attenuator 5. In addition, a rounding process such as a noise shaving process or a dither process is performed, and a waveform process is performed such that an attenuated digital output signal having a data length equivalent to the data length of the digital input signal is obtained.

Accordingly, the digital input signal a selected by the switch circuit 3 is a PCM signal formed of 16 bits from the least significant bit LSB to the most significant bit MSB as shown in FIG. First, using the digital attenuator 5 for a, the data length (16
) Is doubled to 32 bits to generate an expanded digital signal b and input it to the waveform processing circuit 6.

The expanded digital signal b corresponds to the signal data attenuated by the digital attenuator 5, so that the original 16-bit signal is reduced to 16 bits or less of the digital input signal a. Here, in the related art, the lower bits are simply truncated for attenuation, but in the present embodiment, they are not truncated at all since they are doubled like the expanded digital signal b.

The 32-bit decompressed digital signal b is subjected to a rounding process such as a well-known noise shaving process or a well-known dither process on the data of the 16th bit or less by the waveform processing circuit 6 to generate a digital output signal c. like,
The data is rounded to a 16-bit data frame equivalent to 16 which is the number of bits of the original digital input signal a.

Since the digital output signal c has been subjected to the rounding process, a noise component is added to the high frequency range. The rounding process is performed in the lower 3 to 4 bits of the predetermined data length. It is configured to perform in a digital code domain corresponding to a voice band of 10 kHz or more, which has a low perceptual sensitivity, so that the original voice component has the 16-bit accuracy of the original digital input signal a. And the dynamic range is substantially ensured.

It should be noted that the present invention relates to a PC as described above.
Not only for M16 bit signals, but also for DVD
As may be seen from the above, a PCM 24-bit signal may be used, and the same applies to data having a bit number less than 16 bits. Also, when converting a digital input signal into an expanded digital signal, not only the case where the original number of bits is twice, but also, for example, expansion of 16 bits to 20 bits, expansion of 24 bits, etc. Is also good.

The digital attenuator 5 constitutes "first signal processing means" and the waveform processing circuit 6 constitutes "second signal processing means". Of course, the circuit configuration or the configuration of executing the program software may be applied so that the process of ") is performed in unison.

Further, the form of a digital signal to which the present invention is applied is a 16-bit PCM widely used in CDs and the like.
It goes without saying that the same applies to the compressed data such as the ATRAC format as well as the signal.

[0029]

As is apparent from the above description, the digital attenuator circuit according to the present invention generates an expanded digital signal having an increased data length of a digital input signal, and multiplies the expanded digital signal by a predetermined coefficient to perform digital attenuation processing. A first signal processing means for performing
The lower bits of the expanded digital signal corresponding to the least significant bit of the digital input signal are subjected to rounding processing such as noise shaving processing or dither processing to obtain a data length equivalent to the data length of the digital input signal. And a second signal processing means for performing a waveform process to provide an attenuated digital output signal having
In the case of bit data, for example, when attenuating by -12 dB, the lower two bits of data are not truncated as in the conventional case, but are complementarily processed by rounding. The dynamic range of 16 bits inherently provided can be substantially secured.

Therefore, when an attenuated digital processing is performed by multiplying a code string of a digital input signal composed of PCM data having a predetermined data length by a predetermined coefficient to output an attenuated digital output signal, the attenuating processing is performed. It is possible to provide a digital attenuator circuit that does not substantially cause deterioration of audio quality due to a decrease in accuracy or a decrease in dynamic range.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a circuit configuration of a digital attenuator circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining an attenuation processing operation of the digital attenuator circuit shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 digital signal processing circuit 2 A / D conversion circuit 3 switch circuit 4 digital attenuator circuit 5 digital attenuator 6 waveform processing circuit

Claims (7)

[Claims] A digital attenuator circuit for performing attenuated digital processing by multiplying a code sequence of a digital input signal composed of PCM data having a predetermined data length by a predetermined coefficient to output an attenuated digital output signal; A first signal processing unit that generates a decompressed digital signal having an increased data length and performs a digital attenuation process by multiplying the decompressed digital signal by a predetermined coefficient; and an output of the first signal processing unit. Bits of a part lower than the bits of the decompressed digital signal corresponding to the least significant bit of the digital input signal are subjected to rounding processing such as noise shaving processing or dither processing, and have a data length equivalent to the data length of the digital input signal. A second signal processing means for performing a waveform processing to be an attenuated digital output signal having a data length Digital attenuator circuit, characterized by comprising and. 2. The digital attenuator circuit according to claim 1, wherein the digital input signal input to said first signal processing means is constituted by data obtained by linearly A / D converting an analog sound source. 3. A digital input signal inputted to said first signal processing means is constituted by data obtained by A / D-converting an analog sound source by using a predetermined compression means. Digital attenuator circuit. 4. The apparatus according to claim 1, wherein the rounding processing performed by the second signal processing means is performed in a range of 3 to 4 bits below the predetermined data length. Digital attenuator circuit. 5. The method according to claim 1, wherein the rounding processing performed by the second signal processing means is performed in a digital code area corresponding to a voice band of 10 kHz or more, which has low perceptual sensitivity. Digital attenuator circuit as described. 6. A digital attenuator circuit comprising said first signal processing means and said second signal processing means is used by being inserted in the middle of a digital signal transmission system. Item 6. A digital attenuator circuit according to any one of Items 5. 7. The digital attenuator circuit comprising the first signal processing means and the second signal processing means is used in an input stage of a digital signal recording device. Digital attenuator circuit.