JP3433838B2 - Test signal generator and recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, a CD (compact disc) or a DAT (digital audio tape).
CD player or D that reproduces digital data from
The present invention relates to a test signal generator and a recording medium suitable for use when measuring the characteristics of an AT device or the like.

[0002]

2. Description of the Related Art Conventionally, for example, in the case of measuring frequency characteristics and harmonic distortion of a CD player, etc., a test CD (in which a sine wave with a frequency of, for example, 1000 Hz is recorded as a test signal in the CD player This is done by playing a test CD) and analyzing the resulting playback signal.

[0003]

By the way, when a CD player reproduces a CD on which an audio signal quantized (sampled) by 16 bits is reproduced, the maximum reproduction level is 0 dB. , The audio signal is normally −32767 (= −2 ^k−1 +1)
Through 32767 (= 2 ^k-1 -1), 65535 kinds of bit patterns (quantized values) (sampled values) can be taken (the minimum value -32768 (= -2 ^k-1 ) is usually Not used).

On the other hand, assuming that the sampling frequency of the audio signal reproduced by the CD player is, for example, 44100 Hz, a sine wave having a frequency of 1000 Hz is quantized with a sampling frequency of 44100 Hz and 16 bits into a digital test signal. Is the above-mentioned 32767 to 32.
Of the 767 bit patterns, only 441 types of patterns appear. Therefore, when a test of a CD player (measurement of frequency characteristics, harmonic distortion ratio, etc.) is performed using a test CD on which such a test signal is recorded, there is a problem that an accurate measurement result cannot be obtained. there were.

Therefore, as the test signal to be recorded on the test CD, for example, the nominal value of the frequency is 1000 or 8000H.
A sine wave having a frequency such as 997 or 7993 Hz, which is a prime number close to z, is used.

However, the present inventor has found that the frequency 99
A test signal that is a sine wave of 7 and 7993 Hz is quantized with a sampling frequency of 44100 Hz and 16 bits, and the bit pattern obtained as a result is investigated. As a result, 20541 of the 65535 kinds of bit patterns described above are detected. It turns out that only the pattern of is obtained.

Therefore, even if the prime number close to the nominal value is simply used as the frequency of the sine wave as the test signal, there is a bit pattern that does not appear as a result of the quantization, so that there is a problem in that an accurate measurement result cannot be obtained. .

The present invention has been made in view of such a situation, and makes it possible to obtain an entire bit pattern from a test signal and thereby obtain an accurate measurement result. Is.

[0009]

A test signal generator according to claim 1, which generates a test signal for testing a digital signal processing device for processing a digital signal of a predetermined sampling frequency. In the method, the test signal is a digital sine wave having a sampling interval corresponding to a predetermined sampling frequency, and a sine wave having a frequency at which a bit pattern including all possible bit patterns of the digital signal appears. To do.

In the test signal generator according to the present invention, the digital signal has a quantization resolution of k (k is a positive integer) bits, and -2 ^k-1 +1 to 2 ^k-1 -1. When a bit pattern corresponding to a value in the range is taken and a predetermined sampling frequency is represented by fs, the test signal f satisfies the expression sin (2πf / fs) <1 / (2 ^k−1 −1) And a positive integer that is expressed by a positive integer ratio n / m (n and m are positive integers) and has no common divisor other than 1 with the predetermined sampling frequency fs. It has a frequency of a value multiplied by.

A recording medium according to a third aspect of the present invention records a test signal for testing a digital signal processing device (for example, the CD player 2 shown in FIG. 1) that processes a digital signal of a predetermined sampling frequency. In the recording medium, the test signal is a digital sine wave having a sampling interval corresponding to a predetermined sampling frequency, and a sine wave having a frequency at which a bit pattern including all possible bit patterns of the digital signal appears. Is characterized by.

In the recording medium according to claim 4, the digital signal has a quantization resolution of k (k is a positive integer) bits, and is in the range of -2 ^k-1 +1 to 2 ^k-1 -1. If a predetermined sampling frequency is represented by fs, the test signal is f that satisfies the expression sin (2πf / fs) <1 / (2 ^k−1 −1). Then, what is expressed by a positive integer ratio n / m (n and m are positive integers) is multiplied by a positive integer having a common divisor other than 1 with a predetermined sampling frequency fs. It is characterized by having a frequency of a specified value.

[0013]

In the test signal generator according to the present invention, the test signal is a digital sine wave having a sampling interval corresponding to a predetermined sampling frequency and including all bit patterns that the digital signal can take. Since the sine wave having the frequency at which the pattern appears is generated, it is possible to accurately test the digital signal processing device and thereby obtain an accurate test result.

In the test signal generator according to the present invention, the digital signal has a quantization resolution of k (k is a positive integer) bits, and -2 ^k-1 +1 to 2 ^k-1-. When a bit pattern corresponding to a value in the range of 1 is taken and a predetermined sampling frequency is represented by fs, as a test signal,
A value of f satisfying the expression sin (2πf / fs) <1 / (2 ^k−1 −1) and expressed by a positive integer ratio n / m (n and m are positive integers) is defined as A sine wave having a frequency that is a value obtained by multiplying a positive integer that has no common divisor other than 1 with the sampling frequency fs is generated. Therefore,
Since a bit pattern including all bit patterns that the digital signal can take appears in the test signal, an accurate test result of the digital signal processing device can be obtained.

According to another aspect of the recording medium of the present invention, the test signal is a digital sine wave having a sampling interval corresponding to a predetermined sampling frequency and including all bit patterns that the digital signal can take. The sine wave of the emerging frequency is recorded. Therefore,
An accurate test result can be obtained by reproducing this with a digital signal processing device and performing the test.

In the recording medium according to the fourth aspect, the digital signal has a quantization resolution of k (k is a positive integer) bits and is in the range of -2 ^k-1 +1 to 2 ^k-1 -1. When a bit pattern corresponding to a value in the range is taken and a predetermined sampling frequency is represented by fs, as a test signal, f satisfying the expression sin (2πf / fs) <1 / (2 ^k−1 −1) is used. Therefore, what is expressed by a positive integer ratio n / m (n and m are positive integers) is converted into a positive integer having a common divisor other than 1 with a predetermined sampling frequency fs. A sine wave having a multiplied value frequency is recorded. Therefore, in the test signal, a bit pattern including all the bit patterns that the digital signal can take appears,
An accurate test result can be obtained by reproducing this with a digital signal processing device and performing the test.

[0017]

EXAMPLES Examples of the present invention will be described below.
As a preparation for the preceding step, the principle of the present invention will be described.

For example, when a sine wave with a frequency of 1 Hz is quantized with 16 bits at a sampling frequency of 44100 Hz, which is a typical standard of CD, the above-mentioned 32767 to 3276.
Of the 65535 kinds of bit patterns (all bit patterns obtained by 16-bit quantization when -32768 is not used) corresponding to the value in the range of 7,
Only 20541 types of patterns appear.

This is due to the symmetry of the sine wave (the symmetry between the range 0 to π / 2 and the range π / 2 to π, and π to 3).
symmetry between the range of π / 2 and the range of 3π / 2 to 2π), for 44100 sample points in 1 second,
It is considered that there are 22050 kinds of sample values (sine wave level at each sample point), which is ½ of the maximum value. However, due to quantization (sampling), fractions (components that become quantization noise) are rounded down. Because the bit pattern is rounded off, the bit pattern becomes less than that.

Therefore, when the frequency of the sine wave is set to a positive integer value other than 1 Hz, the sine wave is equal to a sine wave having a frequency of 1 Hz and some of the above-mentioned sample values are thinned out. A sine wave with a frequency of any positive integer value of 16 at a sampling frequency of 44100 Hz
Even if bit quantization is performed, a sine wave with a frequency of 1 Hz, that is, more than 20541 types of bit patterns do not appear.

Here, for the test signal which is a sine wave having the above-mentioned prime frequencies 997 and 7993 Hz, 2
This is the reason why only 0541 types of patterns can be obtained.

Further, from a sine wave having a frequency of 1 Hz such as a sine wave having a frequency of 997 or 7993 Hz, a sine wave having a frequency of 1100 as a common divisor with the sampling frequency of 44100 Hz is used. The same kind of bit pattern can be obtained, but the sampling frequency 44
According to the sine wave whose frequency is a value having a positive integer other than 1 as a common divisor with 100 Hz, the above-mentioned 20541
A bit pattern having a specific value among the bit patterns of the types is skipped, so to speak, at the time of sampling, so that the bit pattern obtained is further reduced.

That is, this allows the sampling frequency 4410
A positive integer other than 1 (2, 3, 3) as a common divisor with 0 Hz
,), For example, a sine wave having a frequency of 1000 Hz can obtain only 441 kinds of bit patterns as described above. Also, the sampling frequency 4
The number of obtained patterns decreases as the frequency of the sine wave having the higher common divisor of 4100 Hz decreases (for example, from the sine wave of the frequency 441 or 6300 Hz, 5 is obtained, respectively).
Only one or seven bit patterns can be obtained).

By the way, when a sine wave having a frequency of 1 Hz is quantized by 16 bits at a sampling frequency of 44100 Hz, 65535 kinds of all bit patterns in the range of −32767 to 32767 do not appear. The change of the sine wave, that is, the frequency is considered to be too fast (too high), so to speak, with respect to the 16-bit quantization process.

The fastest changing portion of the sine wave is where the level is near 0, and when the level of the sine wave at a frequency of 1 Hz is near 0, 16-bit quantization is performed at a sampling frequency of 44100 Hz, the sample value is It changes by almost 2 (the quantization width is 1). Therefore, in order to be able to obtain 65535 kinds of all bit patterns from a 1 Hz sine wave, the sample value may be changed by less than 1 (below) in the vicinity of the level of 0.

That is, assuming that the sine wave is sin (2πft) (where f is the frequency of the sine wave and t is time (sample point)), the sample value at the sample point t = t ₁ next to the sample point t = 0 (Sine wave level) sin (2πft
₁ ) and sample value sin at sample point t = 0
Difference from (2πf × 0) sin (2πft ₁ ) (= sin
If (2πft ₁ ) -0) is less than (less than) the quantization width, 65535 types of all bit patterns can be obtained from this sine wave sin (2πft).

Therefore, when the sampling frequency is fs,
The sample value at the sample point t = t ₁ is sin (2
πf / fs), and when the number of quantization bits is k, the quantization width is 1 / (2 ^k-1 -1) (however, the maximum value of the sine wave level is 0 dB. And the minimum quantization value -2 ^k-1 is not used. Hereinafter, when referring to all bit patterns, it is assumed that the minimum quantization value (bit pattern) at the time of k-bit quantization is not included. From the sine wave of frequency f that satisfies the following inequality:
All bit patterns for k-bit quantization can be obtained.

Sin (2πf / fs) <1 / (2 ^k−1 −1) (1)

Now, assuming that fs = 44100 Hz and k = 16 bits, the equation (1) is f <0.2142. Further, when fs = 48000 Hz and k = 16 bits, the equation (1) is f <0.233 ... Since the equation (1) is an inequality in which the left side is a transcendental function (a function that is not algebraic and is not represented by a polynomial), the solution obtained for f is a transcendental number. When f is a transcendental number, a digital sine wave (discretized sine wave of frequency f) having a frequency f and a sampling interval of 1 / fs is
There is no time to reach the zero level, and therefore includes DC (direct current) component. Therefore, such a sine wave is, as described above,
If it is used as a test signal for testing a CD player or the like, it becomes difficult to obtain an accurate test result.

Therefore, among f satisfying the equation (1), one represented by a positive integer ratio n / m (where n and m are positive integers) is selected. That is, specifically, fs =
44100 Hz, k = 16 bits, f <0.
For example, 0.2 Hz is selected from f that satisfies 2142 ... (In this case, n = 1 and m = 5).

From equation (1), a digital signal obtained by 16-bit quantization at 44100 Hz for one cycle of this sine wave having a frequency of 0.2 Hz, that is, 5 seconds, has all 65535 kinds of bit patterns at the time of 16-bit quantization. Appears.

Therefore, by using this as a test signal for testing a CD player, for example, an accurate test result can be obtained.

When the frequency f of the sine wave as the test signal is 0.2 Hz, it is too low to be practical. Therefore, when the cycle of the sine wave having the frequency of 0.2 Hz is considered to be 1 second which is n / m (= 1/5) times the original cycle (5 seconds), that is, the sine wave having the frequency of 0.2 Hz is obtained. , That m / n
Assuming that the sine wave is 1 Hz, which is (= 5/1) times the frequency, the sampling frequency 44100 Hz is also m / n (=
It can be considered that the frequency is 5/1) times 5 × 44100 Hz.

In this way, the time axis is n / m (= 1/5)
Even if it is multiplied, 1 Hz, which is the frequency of the sine wave, satisfies the equation (1). Therefore, when the sine wave having the frequency of 1 Hz is quantized with 16 bits at the sampling frequency 5 × 44100, All bit patterns can be obtained as in the case.

That is, the common divisor with the sampling frequency 5 × 44100 does not have a value other than 1, for example, 101 (101
Has a common divisor of 1 even in relation to the sampling frequency 44100), and a sampling frequency of 5 × 4
When 16-bit quantization is performed by the 4100, all bit patterns can be obtained from the one second.

Here, when the time axis is multiplied by m / n (= 5/1) and considered on the original time axis, 20.2 (= 101 × 1)
From the sine wave of / 5) Hz, all 5 bit patterns can be obtained by quantizing this 5 (= 1 × 5/1) second by 16 bits at the sampling frequency 44100.

The frequency of the sine wave that can be obtained in the above manner and that can obtain all bit patterns does not have to be a prime number as in the conventional case. That is, on the time axis multiplied by n / m (1/5), the value has a value other than 1 as a common divisor with the sampling frequency 44100 (or 5 × 44100) and is not a prime number, for example, 7999 ( = 19 x
421) Hz and the like are returned to the original time axis on 1599.
Even with a sine wave of 8 (= 7999 × 1/5) Hz, the full bit pattern can be obtained from the 5 seconds.

The duration of a test signal (signal duration) required when testing a CD player is usually 3
Since it is 0 second or 1 minute, the above-mentioned 5 seconds can be easily matched with this continuation time. That is, when n = 1 and m = 5 as described above, the test signal that continues for 30 seconds or 1 minute is, for example, the sine wave (for example, 20.
5 seconds of 2Hz or 1599.8Hz sine wave)
It can be easily generated by repeating 6 (= 30 seconds / 5 seconds) times or 12 (= 1 minute / 5 seconds) times.

The frequency of the sine wave preferably includes (is in) the audible band (for example, in the range of 20 (or 16) to 20000 Hz).

In the above, f <0.2142
Of f satisfying ... 0.2 with n = 1 and m = 5
Hz is used so that n / m is a finite decimal number. In addition to this, n / m should be a cyclic decimal number (those included in the range of rational numbers). You can

For example, when n = 1 and m = 6, the time interval in which 0 appears in the sample value of the sine wave is 6 seconds, and all the bit patterns can be obtained from this 6 second sine wave. Furthermore, since the 6 seconds are consistent with the signal duration described above, the test signal can be easily generated by repeating this for a predetermined number of times (for example, 5 times or 10 times).

Further, even if n / m is a circulating decimal number, a digital sine wave having a frequency satisfying the above-mentioned condition is generated (represented) by appropriately combining integer ratios by, for example, a computer having a finite word length. It is possible to

Next, FIG. 1 shows a configuration of an embodiment of a measuring system using a digital sine wave having a frequency obtained as described above as a test signal. In this measuring system, it is possible to measure the frequency characteristic and the harmonic distortion rate of the CD player 2.

That is, in the CD1, as described above,
The standard of a predetermined CD reproduced by the CD player 2 (for example,
Sampling frequency is 44100Hz and quantization bit number is 1
The frequency (for example, 6 bits) calculated according to
A sine wave of 20.2 Hz, for example, has a sampling frequency of 4
A 16-bit quantized signal at 4100 Hz is recorded as a test signal. Note that only the test signal may be recorded on the CD 1, or the test signal may be recorded together with the audio data and other digital data. However, it is necessary to record a test signal for the time (signal duration) necessary for measuring the frequency characteristic, harmonic distortion, etc. of the CD player 2 by the measuring device 3 on the CD 1. .

The CD player 2 has, for example, a sampling frequency of 4
At 4100 Hz, a CD on which a 16-bit quantized signal is recorded is reproduced. The measuring device 3
A CD obtained by analyzing the output of the CD player 2
It is configured to output the measurement results such as the frequency characteristic of the player 2 and the harmonic distortion rate.

In the measuring system configured as described above, the CD 1 is mounted (set) on the CD player 2 and reproduction is started in accordance with the above-mentioned CD standard. As a result, the test signal recorded on the CD 1 is reproduced, and the reproduced signal is supplied to the measuring device 3. The measuring device 3 analyzes the reproduction signal from the CD player 2 and outputs the measurement result such as the frequency characteristic and the harmonic distortion rate of the CD player 2 obtained as a result.

Since all bit patterns due to 16-bit quantization appear from the test signal recorded on the CD 1, accurate measurement results can be obtained.

Next, FIG. 2 shows a digital signal broadcast (for example, a PC) to which the test signal generator of the present invention is applied.
1 shows the configuration of an embodiment of a digital broadcasting system for performing radio broadcasting using M audio data).

As shown in FIG. 3, the test signal generator 11 is composed of a signal source 21, a level control unit 22, an up converter 23, and an operation unit 24, and outputs the PCM audio data broadcast (transmitted) by the broadcasting station. Standards (eg,
Sampling frequency is 44100Hz and quantization bit number is 1
(For example, 6 bits) and has a frequency (for example, 20.2 Hz) obtained as described above, and the sampling interval is a time corresponding to the sampling frequency of the PCM audio data, for example, 1 / A 44100-second digital sine wave is output as a test signal.

That is, the signal source 21 has a sampling interval of 1 /
The digital sine wave having a predetermined frequency of 44100 seconds is generated and output to the up converter 23. The level controller 22 controls the level (for example, peak-to-peak value) of the digital sine wave generated by the signal source 21 to a predetermined level. The up-converter 23 up-converts the frequency of the digital sine wave from the signal source 21 to, for example, 20.2 Hz described above according to the operation of the operation unit 24, and outputs it as a test signal.

Here, 1 at a sampling frequency of 44100 Hz
Of the frequencies of the sine wave in which all bit patterns appear when 6-bit quantization is performed, those close to the values shown in the "Nominal (Hz)" column of Table 1 are obtained by the above-mentioned method. It is shown in the column of "Actual (Hz)" of No. 1.

[0052]

[Table 1]

In response to the operation, the operation unit 24 raises the frequency of the test signal output from the test signal generator 11 so that the frequency becomes the value shown in the "Actual (Hz)" column of Table 1. The converter 23 is controlled. The operation unit 2
4 is the frequency of the test signal output from the test signal generator 11 by operating 4 in Table 1, “Actual (H
z) ”corresponding to the values shown in the column“ Nominal (H
The value shown in the column of “z)” is displayed on a display unit (not shown).
Therefore, the frequency of the test signal currently being output can be recognized by the user.

The transmitter 12 (FIG. 2) transmits PCM audio data output from a broadcasting device (not shown) and quantized with 16 bits at a sampling frequency of 44100 Hz as a radio wave from an antenna. . Further, the transmitter 12 is also adapted to transmit the test signal from the test signal generator 11 from the antenna as well.

The radio waves transmitted from the antenna are distributed via, for example, a satellite line or a ground line.

In the broadcasting system configured as described above, the frequency of the digital sine wave generated by the signal source 21 in the test signal generator 11 is changed by the up converter 23 according to the operation of the operation unit 24. Is up-converted to any value in the “Actual (Hz)” column and output as a test signal.

This test signal is supplied to the transmitter 12 and transmitted from the antenna. Radio waves from this antenna are received again by the antenna and supplied to the measuring device (neither is shown) via the receiving device.

In the measuring device, the received signal supplied through the receiving device is analyzed, and the resulting measurement result of the frequency characteristic of the receiving device of the broadcasting station or the like and the harmonic distortion ratio is output.

Since all bit patterns at the time of 16-bit quantization appear from the test signal output from the test signal generator 11, an accurate measurement result can be obtained.

Although the present invention has been described above applied to the measurement of the characteristics of the CD player 2 and the receiving device of the broadcasting station, the present invention can be applied to any other processing (including reproduction processing) of a digital signal. It can be applied to the measurement of device characteristics.

In FIG. 1, the characteristic of the CD player 2 is measured by the CD 1 on which the test signal is recorded, but in addition to this, the test signal may be digital data such as DAT or magneto-optical disk. It is possible to record in a recording medium for recording. In this case, it is possible to accurately measure the characteristics of the reproducing device that reproduces the recording medium on which the test signal is recorded.

[0062]

As described above, according to the present invention, it is possible to accurately test the digital signal processing device and to obtain accurate test results.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a measurement system to which the present invention is applied.

FIG. 2 is a block diagram showing the configuration of an embodiment of a broadcasting system to which the present invention is applied.

3 is a block diagram showing a detailed configuration of a test signal generator 11 in the embodiment of FIG.

[Explanation of symbols]

1 CD 2 CD player 3 measuring instruments 11 Test signal generator 12 transmitter 21 signal source 22 Level control section 23 Upconverter 24 Operation part

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Claims (4)

(57) [Claims] 1. A test signal generator for generating a test signal for testing a digital signal processing device for processing a digital signal of a predetermined sampling frequency, wherein the test signal corresponds to the predetermined sampling frequency. A test signal generator, wherein the test signal generator is a digital sine wave having a sample interval, and a sine wave having a frequency at which a bit pattern including all bit patterns that the digital signal can take appears. 2. A bit pattern in which the digital signal has a quantization resolution of k (k is a positive integer) bits and corresponds to a value in the range of −2 ^k−1 +1 to 2 ^k−1 −1. And the predetermined sampling frequency is represented by fs, the test signal is f satisfying the expression sin (2πf / fs) <1 / (2 ^k−1 −1) and is a positive integer. What is expressed by the ratio n / m (n and m are positive integers) is the predetermined sampling frequency f.
2. A frequency having a value obtained by multiplying a positive integer having a relationship with s that has no common divisor other than 1 by one.
Test signal generator described in. 3. A recording medium having a test signal recorded therein for testing a digital signal processing device for processing a digital signal having a predetermined sampling frequency, wherein the test signal is a sample corresponding to the predetermined sampling frequency. A recording medium, characterized in that it is a digital sine wave of intervals, and a sine wave of a frequency at which a bit pattern including all bit patterns that the digital signal can take appears. 4. A bit pattern in which the digital signal has a quantization resolution of k (k is a positive integer) bits and corresponds to a value in the range of −2 ^k−1 +1 to 2 ^k−1 −1. And the predetermined sampling frequency is represented by fs, the test signal is f satisfying the expression sin (2πf / fs) <1 / (2 ^k−1 −1) and is a positive integer. What is expressed by the ratio n / m (n and m are positive integers) is the predetermined sampling frequency f.
claim characterized in that it has a frequency of positive value obtained by multiplying the integer in common divisor no relationship other than 1 between the s 3
The recording medium described in.