JPH0472941A - Encoder for audio signal - Google Patents

Abstract

PURPOSE:To obtain an audio signal with less reflected noise even in the mode of a low bit rate by controlling a data at a highest frequency with less effect in an audible sense among plural bands not to be sent when the mode of a lowest bit rate is selected. CONSTITUTION:This encoder is provided with a switching signal generating circuit 33 as a mode selection means to select one of plural modes of a different bit rate, and when the mode of a lowest bit rate is selected at least in response to an output of the switching signal generating circuit 33, a switch circuit 32 is controlled so that a data at a highest frequency (such as a band B4) giving less adverse effect on an audible sense among those plural bands is not sent. Thus, audio data in the modes of plural different bit rates are obtained and an audio signal with less reflected noise even is obtained even in the mode of a low bit rate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an audio signal that obtains encoded output according to a plurality of modes with different bit rates. In an audio signal encoding device that encodes and transmits an audio signal, when one of a plurality of modes is selected and at least the mode with the lowest bit rate is selected, the highest frequency data is not transmitted. By controlling the bit rate, it is possible to obtain audio data with a compressed bit rate according to multiple modes with a simple configuration, and an audio signal with less aliasing noise can be obtained even in a low bit rate mode. The present invention provides an encoding device.

[Conventional technology]

Conventional devices that handle digital data, such as digital audio data, include, for example, so-called compact discs (CDs) and digital audio tape recorders (DATs). In recent years, in order to be able to respond to a variety of needs in those that handle such digital audio data, in other words, not only audio information, but also images (natural images, animation, computer graphics, etc.), various data,
In order to be able to handle text information, etc., data may be recorded in a plurality of different modes on the same medium.

An example of a device that records data using a plurality of motes as described above is the so-called CD-1 (CD ink active). Tables 1 and 2 show some of the unified standards for CD-I.

Table 1 Table 2 For this CD-■, as shown in Tables 1 and 2 above, the mote of the CD digital audio and the level A
, B, and C modes have been standardized.

Among these four modes, the CD digital audio mode encodes the audio signal using 16-bit PCM (pulse coding), and uses the levels AB,
The three modes of C are 8-bit or 4-bit ADPC.
The audio signal is encoded by M (adaptive differential pulse encoding). In other words, the three modes of levels A, B, and C of this CD-1 handle other data such as video as well as audio data, and the levels A, B, and C are different from the 16-bit mode of the conventional CD. The remaining bits obtained by compressing audio data to 8 bits or 4 bits are used for data such as video.

[Problem to be solved by the invention]

By the way, when obtaining audio data in multiple modes with different bit rates, such as the four modes in the CD-1, various methods are used to obtain data compressed to a low bit rate. There is. A method to obtain data compressed to a low bit rate is, for example, to perform orthogonal transformation of the input audio signal on the frequency axis and to avoid encoding part of the resulting frequency data. In some cases, a method is used to reduce the number of bits that should originally be given to the data in order to obtain data with a compressed bit rate as a whole. If such orthogonal transformation is used, signal processing on the frequency axis can be performed, so data in modes with different bit rates can be easily obtained.

However, if such orthogonal transformation is used to obtain, for example, low bit rate encoded data, so-called aliasing noise (aliasing noise) becomes noticeable when the low bit rate encoded data is decoded.

For this reason, in a configuration for obtaining low bit rate encoded data using orthogonal transformation as described above, a so-called aliasing filter that attenuates high-frequency components is usually inserted before the orthogonal transformation. Connecting is done.

However, when trying to obtain encoded data in multiple modes with different bit rates as described above with an encoding configuration using this orthogonal transform, it is necessary to vary the characteristics of the aliasing filter in accordance with the mode. As a result, the configuration becomes complicated.

Therefore, the present invention was proposed in view of the above-mentioned circumstances, and it is possible to obtain audio data in a plurality of mutually different bit rate modes with a simple configuration, and eliminates aliasing noise even in a low bit rate mote. It is an object of the present invention to provide an audio signal encoding device that can obtain an audio signal with less noise.

The mode selection means has a mode selection means configured such that when at least the mode with the lowest bit rate is selected according to the output of the mode selection means, a control clause is configured so as not to transmit data in the highest band among the plurality of bands. It was designed to do so.

[Effect]

According to the present invention, when a mode with a low bit rate is selected, data at this low bit rate is obtained by not transmitting high-band audio data that would have little negative impact even if deleted on the auditory sense. ing.

[Means to solve the problem]

The audio signal encoding device of the present invention has been proposed to achieve the above-mentioned object, and divides an input audio signal into a plurality of bands, and encodes and transmits data for each band. [Embodiment] An embodiment to which the present invention is applied will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a schematic configuration of an audio signal encoding apparatus according to an embodiment of the present invention.

The device of this embodiment shown in FIG. 1 inputs an input audio signal into a plurality of bands (for example, four bands
1 to B4), and in an audio signal encoding device that encodes and transmits data for each band, mode selection means selects one of a plurality of mutually different bit rate modes. When at least the mode with the lowest bit rate is selected according to the output of the switch change signal generation circuit 33, the switch circuit 32 is controlled to select one of the plurality of bands. Control is performed so as not to transmit data in the highest frequency band (for example, band B4) that has the least adverse effect on the auditory sense.

That is, in the apparatus shown in FIG. 1, the input audio signal is a digital signal obtained by sampling the audio waveform, and this digital signal is input to the input terminal 1.
is supplied to. This input audio signal is passed through a bandpass filter (BPF) with a different passband.
) sent to 11-14. Here, for example, assume that the passband of BPFII is the lowest, and below, BPF12, 13
The passband is made higher in this order, and the passband of the BPF 14 is made the highest one. By passing through these BPF II-14, the input audio signal is divided into four bands 81-B4 as shown in FIG. In this embodiment, the bandwidth of each band obtained by dividing the BPF 14 to 14 is made equal as shown in FIG. The division may be performed using a so-called critical band, in which the bandwidth becomes wider as the bandwidth increases.

The signals of each frequency band from the BPF II-14 are sent to quantizers 21-24, respectively.

These quantizers 21 to 24 each requantize the input digital signal with the same number of quantization bits.

Therefore, the number of bits of data obtained by combining the output data of each of these quantizers 21 to 24 in a combining circuit 31 composed of a multiplexer, etc. The data is the total number of bits in focus. Note that although the encoding in this embodiment uses normal PCM or ADPCM, it is also possible to adopt a configuration in which, for example, signals in each frequency band are further orthogonally transformed and then encoded.

Here, data obtained by quantizing the BPFs 13 and 14 whose passband is the high frequency band by the quantizers 23 and 24 is sent to the switch circuit 32. The output data of the quantizer 23 is sent to the switch 32a of the switch circuit 32, and the output data of the quantizer 24 is sent to the switch 32b.

Further, the terminal 2 is supplied with mode signals corresponding to each of the plurality of modes having mutually different bit rates. This mode signal is sent to a switch changeover signal generation circuit 33 that generates a switch changeover control signal for the switch circuit 32 in accordance with the mode signal. Therefore, switching of the switch circuit 32 is controlled in accordance with the switch switching control signal from the switch switching signal generating circuit 33. That is, when the mode signal is, for example, a signal of a mode indicating the lowest bit rate, the switch switching signal generation circuit 33 outputs the switch 32a of the switch circuit 32,
A switch changeover control signal is output to turn off both the switches 32b and 32b. Further, when the mode signal is, for example, a signal of a mode indicating the second lowest bit rate, the switch changeover signal generation circuit 33 turns on the switch 32a of the switch circuit 32,
A switch changeover control signal for turning off the switch 32b is output. Further, if the mode signal is not, for example, a signal of a mode indicating the lowest bit rate or a signal of a mode indicating the second lowest bit rate, the switch changeover signal generating circuit 33 outputs the switch 32a of the switch circuit 32. , 32b are both turned on.

From the above, for example, when the mode signal is a mode signal indicating the lowest bit rate, the number of bits of data obtained from the synthesis circuit 31 is equal to the number of bits from the quantizers 21 and 22. This is the number of bits in which the data is combined. That is, for example, if the number of bits of the output data of each quantizer is 4 bits, the data will be 8 bits. Further, when the mode signal is a signal of a mode indicating the second lowest bit rate, the number of bits output from the synthesis circuit 31 is the result of combining the data from the quantizers 21, 22 and 23.

For example, if the output data of each quantizer is the above-mentioned 4 bits, it becomes 12 bits. Furthermore, if the mode signal is not a signal of a mode indicating the lowest or second lowest bit rate, the synthesis circuit 31 synthesizes the data from the quantizers 21, 22, and 23. The number of bits.

For example, if each quantizer is 4 bits as described above, it becomes 16 bits.

In other words, in the device of this embodiment, when a signal in a mode showing the lowest bit rate and a signal in a mode showing the second lowest bit rate are selected, the signal in the mode showing the second lowest bit rate is selected, and the signal in the mode showing the second lowest bit rate is selected. audio signals in the range,
Transmission is prevented by turning off the switch circuit 32. Also, before quantization in each quantizer,
Since the above-mentioned high-frequency components are not removed, aliasing noise on the decoding side is reduced.

The output data from the synthesis circuit 31 is output from the output terminal 3 as encoded data, and is recorded on, for example, a recording medium. In addition, the mode signal from terminal 2 is also
The signal is output from the output terminal 4 and simultaneously recorded on the recording medium.

As described above, the audio signal encoding device of this embodiment includes the switch changeover signal generation circuit 33 as a mode selection means configured to select one of a plurality of mutually different bit rate modes. When at least the mode with the lowest bit rate is selected in accordance with the output of the switch changeover signal generation circuit 33, the switch circuit 32 is controlled to ), it is possible to obtain audio data in multiple different bit rate modes with a simple configuration, and audio signals with less aliasing noise can be obtained even in low bit rate modes. You will be able to get it.

Therefore, if the device of this embodiment is applied to, for example, the above-mentioned CD-1, the CD audio mode, level A, B, C
You will be able to obtain audio signals in each mode.

〔Effect of the invention〕

The audio signal encoding device of the present invention includes mode selection means for selecting one of a plurality of mutually different bit rate modes, and at least the highest bit rate mode is selected according to the output of the mode selection means. When a mode with a low bit rate is selected, the data in the highest frequency range, which has the least negative impact on hearing, is controlled so as not to be transmitted, so that it is possible to use multiple different bit rate modes with a simple configuration. of audio data, and audio signals with less aliasing noise can be obtained even in low bit rate mode.

Therefore, if the device of the present invention is applied to CD-1, for example, CD audio mode, level A, B.

It becomes possible to obtain audio signals of each mode of C.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an audio signal encoding apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining band division in the embodiment of the present invention. 11-14...BPF 21-24...Quantizer 31......Synthesizing circuit 32...
......Switch circuit 33...
...Switch switching signal generation circuit Patent applicant Sony Corporation representative Patent attorney Akira Koba (and 2 others) Ha/, Vtsu

Claims (1)

[Claims] In an audio signal encoding device that divides an input audio signal into a plurality of bands and encodes and transmits data for each band, one of a plurality of modes with mutually different bit rates is provided. and mode selection means configured to select the mode selection means, and at least when the mode with the lowest bit rate is selected according to the output of the mode selection means, data in the highest band among the plurality of bands is not transmitted. What is claimed is: 1. An audio signal encoding device characterized in that the audio signal encoding device is configured to control.