Spectrum display device for audio signals

• US 4,665,494 A
• Filed: 12/16/1983
• Issued: 05/12/1987
• Est. Priority Date: 12/17/1982
• Status: Expired due to Term

• Current Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation)
• Original Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation)
• Inventors: Otsuki, Zenju, Inami, Mamoru, Tanaka, Yoshiaki
• Primary Examiner(s): Chin, Gary
• Application Number:
  US06/562,183
• Time in Patent Office: 1,243 Days
• Field of Search: 364/483, 364/484, 364/485, 364/726, 364/724, 324/77 B, 324/77 E, 324/78 F, 358/138, 340/347 SH
• US Class Current: 702/77
• CPC Class Codes: G01H 3/08 Analysing frequencies present in complex vibrations, e.g. comparing harmonics present acoustic presence detection G01V1/001
• CPC Class Codes: G01R 13/405 using a plurality of active, i.e. light emitting, e.g. electro-luminescent elements, i.e. bar graphs
• CPC Class Codes: G01R 23/18 with provision for recording frequency spectrum

Abstract

An input audio signal is AD converted into digital signals which are processed by a central processing unit (CPU) in which Fast Fourier Transform (FFT) operation and power spectrum calculation are effected. As a result power spectrum data is obtained, and then position determination is effected to determine the position of each bar of a bar graph to be displayed on a display unit screen, according to the power level at different frequencies within the spectrum of the audio signal. Pattern data is then produced in correspondence with the determined position, and output data from the CPU is fed via a video display processor to a video RAM, thereby displaying the spectrum by way of a predetermined pattern of a bar graph on the screen. In order to reduce the number of digital data used in FFT operation the input audio signal may be divided into a plurality of different frequency bands so that different sampling frequencies are used for AD conversion of signals of respective bands. As a result, operating time is reduced. To further reduce the operating time the CPU may be arranged to execute parallel operations in various manners. Furthermore, two or more CPUs may be employed to further increase the operating speed.

Claims

1. A spectrum display device for an audio signal comprising:

(a) band-separating means for dividing an input audio signal into plural analog signals each having one of plural different frequency bands;

(b) analog-to-digital converting means for converting said analog signals derived from said band-separating means into digital signals at a sampling frequency;

(c) selecting means for selectively and sequentially applying said analog signals derived from said band-separating means to said analog-to-digital converting means;

(d) means for varying said sampling frequency to said analog-to-digital converting means as a function of the frequency band selected to be supplied to said converting means;

(e) a central processing unit for (i) effecting FFT operation in connection with the digital signals derived from said analog-to-digital converting means, (ii) effecting power spectrum calculation in connection with the result of the FFT operation to obtain power spectrum data, (iii) converting said power spectrum data into pattern information corresponding to the amplitude of a plurality of frequencies within a spectrum of said input audio signal, and (iv) deriving data indicative of said pattern information; and

(f) a video display processor including a display unit having a screen and a video RAM, said display processor being responsive to data derived from said central processing unit for generating a video signal using picture data stored in the video RAM to thereby display a power spectrum by way of said pattern on said screen of said display unit such that said plurality of frequencies within said spectrum are arranged in sequence on the screen.

2. A spectrum display deviced as claimed in claim 1, wherein said band-separating means comprises a plurality of band pass filters.

3. A spectrum display device as claimed in claim 1, wherein said selecting means comprises a multiplexer having a switching operation controlled by said central processing unit.

4. A spectrum display device as claimed in claim 1, wherein said means for varying comprises another central processing unit.

5. A spectrum display device as claimed in claim 1, further comprising:

(a) an adder for deriving a sum signal by linearly combining first and second signal components of said input audio signal;

(b) a subtractor for deriving a difference signal by linearly combining said first and second signal components;

(c) a selection circuit having input signals responsive to;

said first and second signal components, sum signal and difference signal for coupling one of the input signals thereof to said analog-to-digital converting means.

6. A spectrum display device as claimed in claim 1, wherein said central processing unit is arranged to operate to (a) cause said analog-to-digital converting means and said selecting means to sequentially convert a plurality of analog frequency band signals into digital signals, (b) subsequently sequentially execute FFT operations in connection with a plurality of digital data to said plurality of frequency bands, and (c) subsequently sequentially execute power spectrum calculations in connection with a plurality of results of said FFT operations the amplitude of plural frequencies within a spectrum of said input audio signal, and (iv) deriving data indicative of said pattern information, one of said central processing units being arranged to effect FFT operation and power spectrum calculation in connection with the digital signals of a predetermined frequency band among said plurality of frequency bands, said plurality of central processing units being connected to be mutually responsive to each other so that given operations are performed at appropriate timing in each of said plurality of central processing units;

and

(d) a video display processor having a display unit with a screen and a video RAM for storing picture data from said plurality of central processing units for generating a video signal using the picture data stored in the video RAM to thereby display a power spectrum by way of said pattern on a screen of a display unit such that said plurality of frequencies within said spectrum are arranged in sequence.

7. A spectrum display device as claimed in claim 1 wherein said central processing unit includes a memory, further comprising:

(a) an absolute value detecting circuit responsive to said input audio signal for deriving a unidirectional output signal and for supplying said analog-to-digital converting means with the unidirectional output signal; and

(b) a polarity detector responsive to said input audio signal for deriving an output signal indicative of the polarity of the input audio signal and for supplying said central processing unit with the output signal indicative of the input audio signal polarity so that the output signal from said polarity detector and the digital signals from said analog-to-digital converting means are stored in the central processing unit memory.

8. A spectrum display device as claimed in claim 1, wherein said central processing unit is arranged to execute substantially parallel operations by way of a plurality of routines such that operations for controlling said analog-to-digital converting means are repeatedly executed during an interval in which remaining operations are executed.

9. A spectrum display device as claimed in claim 8, wherein said central processing unit is arranged to execute an interrupt service routine for controlling said analog-to-digital converting means.

10. A spectrum display device as claimed in claim 9, wherein said central processing unit comprises an internal counter for setting a sampling period for the analog-to-digital converting means, said central processing unit being arranged to execute said interrupt service routine during an interval of said sampling period.

11. A spectrum display device as claimed in claim 1, wherein said central processing unit is arranged to execute an interrupt service routine for controlling said analog-to-digital converting means.

12. A spectrum display device as claimed in claim 11, wherein said central processing unit comprises an internal counter for setting a sampling period for the analog-to-digital converting means, said central processing unit being arranged to execute said interrupt service routine during an interval of said sampling period.

13. A spectrum display device as claimed in claim 1, wherein said central processing unit is arranged to sequentially perform FFT operations in connection with all the digital signals of said respective frequency bands, and then to sequentially perform power spectrum calculations in connection with all the results of said FFT operations.

14. A spectrum display device as claimed in claim 1, wherein said central processing unit is arranged to sequentially perform operations including said FFT operation and power spectrum calculation in connection with the digital signals of one of said respective frequency bands, and then to sequentially perform operations including said FFT operation and power spectrum calculation in connection with the digital signals of another one of said respective frequency bands.

15. A spectrum display device as claimed in claim 1, wherein said central processing unit is arranged to effect said power spectrum calculation in connection with each of said plurality of frequency bands such that a plurality of amplitude data in each of plural frequencies within each frequency band are obtained first, and then a maximum amplitude datum among said plural amplitude data is used as spectrum data to represent the amplitude in each of said plurality of frequency bands.

16. A spectrum display device for an audio signal comprising:

(a) band-separating means for dividing an input audio signal into plural signals each having one of plural frequency bands;

(b) a plurality of analog-to-digital converting means for respectively simultaneously converting a plurality of output signals from said band-separating means into digital signals at different sampling frequencies;

(c) a central processing unit for effecting (i) FFT operation in connection with the digital signals derived from said plurality of analog-to-digital converting means, (ii) power spectrum calculation in connection with the result of the FFT operation to obtain power spectrum data, (iii) converting said power spectrum data into pattern information corresponding to the amplitude of a plurality of frequencies within a spectrum of said input audio signal, and (iv) deriving data indicative of said pattern information; and

(d) a video display processor having a display unit having a screen and video RAM for storing picture data, said display processor being supplied with the pattern information data from said central processing unit for generating a video signal in response to the picture data stored in the video RAM to thereby display a power spectrum by way of said pattern on the screen of the display unit such that said plural frequencies within said spectrum are arranged in sequence on the screen of the display unit.

17. A spectrum display device for an audio signal comprising:

(a) band-separating means for dividing an input audio signal into several signals one for each of plural frequency bands;

(b) analog-to-digital converting means for respectively converting a plurality of output signals derived from said band-separating means into digital signals at different sampling frequencies;

(c) a plurality of central processing units for (i) effecting FFT operation in connection with the digital signals derived from said analog-to-digital converting means, (ii) effecting power spectrum calculation in connection with the result of the FFT operation to obtain power spectrum data, (iii) converting said power spectrum data into pattern information corresponding to amplitudes of a plurality of frequencies within a spectrum of said input audio signal, and (iv) deriving data indicative of said pattern information, one of said central processing units being arranged to effect FFT operation and power spectrum calculation in connection with the digital signals of a predetermined frequency band among said plurality of frequency bands, said plurality of central processing units being connected to be mutually responsive to each other so that given operations are performed with appropriate timing in each of said plurality of central processing units; and

(d) a video display processor having a display unit with a screen and a video RAM for storing picture data, said display processor being supplied with the output data from said plurality of central processing units for generating a video signal using the picture data stored in the video RAM to thereby display a power spectrum by way of said pattern on the screen of the display unit such that said plurality of frequencies within said spectrum are arranged in sequence.

18. A spectrum display device for an audio signal comprising:

(a) band-separating means for dividing an input audio signal into several signals one for each of plural frequency bands;

(b) a plurality of analog-to-digital converting means for respectively simultaneously converting a plurality of output signals from said band-separating means into digital signals at different sampling frequencies;

(c) a plurality of central processing units for (i) effecting FFT operation in connection with the digital signals derived from said plurality of analog-to-digital converting means, (ii) effecting power spectrum calculation in connection with the result of the FFT operation to obtain power spectrum data, (iii) converting said power spectrum data into pattern information corresponding to the amplitudes of plural frequencies within a spectrum of said input audio signal, and (iv) deriving data indicative of said pattern information, one of said central processing units being arranged to effect FFT operation and power spectrum calculation in connection with the digital signals of a predetermined frequency band among said plurality of frequency bands, said plurality of central processing units being connected to be mutually responsive to each other so that given operations are performed at appropriate timing in each of said plurality of central processing units; and

(d) a video display processor having a display unit with a screen and a video RAM for storing picture data, said display processor being supplied with the output data from said plurality of central processing units for generating a video signal using the picture data stored in the video RAM to thereby display a power spectrum by way of said pattern on a screen of a display unit such that said plurality of frequencies within said spectrum are arranged in sequence.

19. Apparatus for processing an analog signal having a predetermined frequency range and converting said analog signal into a plurality of digital signals, each of said digital signals representing the amplitude of the analog signal in each of plural different bands in the predetermined frequency range, each of said ranges having a maximum frequency, comprising means responsive to the analog signal for separating said analog signal into the plural different bands whereby plural further analog signals, one for each of the bands, are derived, means for converting each of the plural further analog signals into a separate digital signal, said means for converting having a different sampling frequency associated with each of the plural further analog signals, the different sampling frequency for each of the plural further analog signals being arranged so that the sampling frequency increases with increasing maximum frequencies associated with each band, and digital signal processing means for processing the separate digital signals derived by the means for converting.

20. The apparatus of claim 19 wherein the digital signal processing means includes means for deriving an indication of the amplitude of the digital signal derived by the means for converting for each of the plural different bands.

21. The apparatus of claim 20 further including means responsive to the indication of each digital signal amplitude and an indication of the band associated therewith for displaying each of the amplitude indications as a discrete length along a first direction of an X-Y plot and for displaying the associated band at a different position along a second direction of the plot.

22. A method of displaying a spectrum of an audio signal comprising:

(a) separating an input audio signal into a plurality of output signals one for each of plural frequency bands;

(b) respectively converting the plurality of output signals into digital signals at different sampling frequencies;

(c) activating plural central processing units to;

(i) perform FFT operations on the converted digital signals, (ii) perform a power spectrum calculation on the results of the FFT operations to obtain power spectrum data, (iii) convert said power spectrum data into pattern information corresponding to amplitudes of plural frequencies within a spectrum of said input audio signal, and (iv) derive data indicative of said pattern information, one of said central processing units performing an FFT operation and power spectrum calculation in connection with the digital signal of a predetermined frequency band among said plurality of frequency bands, said plural central processing units being mutually responsive to each other so that given operations are performed with appropriate timing in each of said plural central processing units; and

(d) activating a video display processor so it is supplied with the output data of said plural central processing units to generate a video signal using picture data stored in a video RAM to thereby display a power spectrum by way of said pattern on a screen of a display unit such that said plural frequencies within said spectrum are arranged in sequence.

23. A method of displaying a spectrum of an audio signal comprising:

(a) separating an input audio signal into a plurality of output signals one for each of plural frequency bands;

(b) respectively simultaneously converting the plurality of output signals into digital signals at different sampling frequencies;

(c) activating plural central processing units to;

(i) perform FFT operations on the converted digital signals, (ii) perform a power spectrum calculation on the result of the FFT operations to obtain power spectrum data, (iii) convert said power spectrum data into pattern information corresponding to the amplitudes of plural frequencies within a spectrum of said input audio signal, and (iv) derive data indicative of said pattern information, one of said central processing units performing an FFT operation and power spectrum calculation in connection with the digital signals of a predetermined frequency band among said plurality of frequency bands, said plural central processing units being mutually responsive to each other so that given operations are performed at appropriate timing in each of said plural central processing units; and

(d) activating a video display processor so it is supplied with the output data of said plural central processing units to generate a video signal using picture data stored in a video RAM to thereby display a power spectrum by way of said pattern on a screen of a display unit such that said plural frequencies within said spectrum are arranged in sequence.