JPH0438477A - Method for measuring delay time of audio amplifier - Google Patents

Abstract

PURPOSE:To shorten a measuring time by subjecting the response output from an audio amplifier due to the input of an impulse wave to discrete Fourier transformation and calculating a phase with respect to respective required frequency components from a complex spectrum to calculate the delay time difference between other respective frequency components to a reference frequency component. CONSTITUTION:An analogue impulse wave is inputted to an audio amplifier 12 to be measured from a signal generator 14. The impulse response output of the audio amplifier 12 to be measured at this time is converted to a digital signal by an A/D converter to be subjected to Fourier transform by a discrete Fourier transformation device 16 like an FFT. The impulse wave is a multiple sine wave having infinite frequency components respectively starting from a zero phase and the complex spectra of respective frequency components are obtained from the transformation device 16. From the real and imaginary parts of the complex spectra with respect to required frequencies among them, for example, 1 kHz, the phases of said frequencies (spectra) are operated and the delay time of these phases is operated. For example, 1 kHz is set to reference frequency and the delay time differences with other frequency components to the reference frequency are respectively calculated. By this method, the delay time of each required frequency can be obtained by one measurement and a measuring time can be markedly shortened. Further, a delay time can be measured even in such a case that the audio amplifier to be measured is digital input and output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring delay time of an audio amplifier, in which the delay time of each frequency component of the audio amplifier is determined as a difference from the delay time of a reference frequency.

``Prior art J'' Conventional delay time measurement of audio amplifiers was performed as shown in Fig. 6. That is, a sine wave signal of a certain frequency is generated from a signal generator 11, and the sine wave signal is subjected to The signal is supplied to the audio amplifier 12 to be measured, the phase difference between the output of the audio amplifier 12 under test and the output of the signal generator 11 is measured with a phase meter 13, and the signal generator 11 is similarly supplied.
The frequency of the output sine wave signal is changed, and each phase difference between the input signal and output signal of the audio amplifier under test 12 is measured for several frequencies. Thereafter, a delay time is calculated from the phase difference measured for each frequency, and using the delay time for one frequency as a reference, the difference between this delay time and the delay time for each other frequency is determined.

``Problem to be Solved by the Invention'' In this conventional measurement method, sine wave signals are generated one by one for multiple frequencies and the phase difference is measured, so the disadvantage is that the measurement takes time. was there.

Some audio amplifiers are equipped with an internal digital equalizer so that the equalization frequency characteristics can be set appropriately. In such audio amplifiers, the input and/or output may be digital signals, and it is not possible to measure the delay time using the measurement method shown in Figure 6 for audio amplifiers that input or output digital signals. could not.

According to the present invention, an impulse wave is input to the audio amplifier under test, the response output from the audio amplifier is subjected to discrete Fourier transform, and the required complex spectrum is obtained from the complex spectrum that is the result of the transform. The phase of each frequency component is determined, and the delay time difference of each other frequency component with respect to the reference frequency component is determined from these phases.

Embodiment J FIG. 1 shows an embodiment of the present invention, in which the present invention is applied to an audio amplifier that inputs and outputs analog signals. The output of the audio amplifier under test 12 at that time, that is, the impulse response output, is converted into a digital signal by the AD converter 15, and the digital impulse response signal is subjected to FFT (fast Fourier transform). Fourier transform is performed using a discrete Two-Elli transformer 16, such as the following.

The impulse wave is a multiple sine wave with infinite frequency components, each starting from zero phase, so that the discrete Zuerli transformer 16 provides a complex spectrum of each frequency component. The required frequency, e.g. IK7, 2KH
The real part R of the complex spectrum for z, ± 3, 7 ± 4
e1 (i=1, 23, -) and the imaginary part 1mi (i=1.
2.3. -) is obtained as shown in FIG. The phase θH=tan-' I mi/Rei of the frequency (spectrum) is calculated from the real part Rei and the imaginary part ll1i.

From these phases θ, there is a delay time τ at a frequency of 1 KHz.

--θi (360°X i xlooO SE) are calculated respectively. Furthermore, one frequency, for example, IKI (where z is a reference frequency, the delay time difference τ2-τ1.τ3-τ1.τ between the reference frequency component and each other frequency component.

Find τ1 for each.

By inputting the impulse wave in this way, 1
The required delay time difference between each frequency component and the reference frequency component can be obtained by measuring the required times.

In the third time, the audio amplifier 12 under test has digital input,
This is an example in the case of digital output. In this case, a digital impulse wave may be generated from the signal generator 17 and applied to the audio amplifier under test I2, and the digital output at that time may be input directly to the discrete Fourier transformer 16.

In FIG. 4, the audio amplifier 12 under test is digitally powered,
In the case of analog output, in this case, a digital impulse wave is input to the audio amplifier under test 12, and the analog output at that time is converted to a digital signal by the AD converter 15 and then supplied to the discrete Fourier transformer 16. . FIG. 5 shows a case where the audio amplifier under test 12 has analog input and digital output. In the second case, an analog impulse wave is supplied to the audio amplifier under test 12, and the digital output at that time is sent to the discrete Fourier transformer 16. ``Effects of the invention'' that can be supplied directly As described above, according to the present invention, by applying an impulse wave to the audio amplifier under test and subjecting the output to M-number Fourier transform, the required amount can be obtained in one measurement. The delay time of each frequency component can be obtained, and the measurement time can be significantly shortened compared to the conventional method. It is also possible to measure when the audio amplifier under test has digital power and/or output.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the real part and imaginary part, phase, and delay time of a complex spectrum obtained by discrete Fourier transform, and FIGS. FIG. 5 is a schematic diagram showing other embodiments of the present invention, and Part 6 is a block diagram showing a conventional measuring method. Student 1 Student 2 Medical Enka kHz kHz kHz kHz 2 kHz Real part Re+ ez e3 e4 Imaginary part rrn m2 m3 m4! Between Enbe 1 total time difference τ2-τ1 m3-m1 τ4-τ1 Cow 3 figures Trees 5 decoys 6 decoys

Claims (1)

[Claims] (1) Input an impulse wave to the audio amplifier under test, perform discrete Fourier transform on the response output from the audio amplifier, calculate the phase of each required frequency component from the complex spectrum that is the result of the discrete Fourier transform, and 1. A method for measuring delay time of an audio amplifier, characterized in that the delay time difference of each other frequency component with respect to a reference frequency component is determined from the phase.