Method and apparatus to evaluate audio equipment via filter banks

Abstract

A testing method or apparatus utilizes filter banks to measure time varying or dynamic harmonic distortion or intermodulation distortion. With a stairstep signal and filter banks, Nth order harmonic and or intermodulation distortion is measured via the filter banks at different offsets provided by an arbitrary low frequency signal. An amplifier with crossover distortion will show increased harmonic and or intermodulation distortion near the zero crossing while providing less distortion in other portions of the transfer curve of the amplifier.

The invention claimed is:  
     
       1. Method for measuring in a time domain, time varying harmonic distortion from an audio device, wherein the audio device has an input and an output, comprising:
 providing a first signal comprising a pulsed, sinusoidal, stairstep, staircase, bipolar, and or arbitrary waveform and a second signal whose frequency is higher than the frequency of the first signal, to an input of the audio device; 
 coupling the output of the audio device to an input of a filter bank, and wherein the filter bank includes, at least one output terminal; 
 measuring the time varying harmonic distortion via measuring or displaying the amplitude level from one of the output terminals of the filter bank to provide the time varying harmonic distortion measurement of the audio device, 
 wherein the time varying harmonic distortion includes a harmonic distortion signal of the second signal, and wherein the harmonic distortion signal of the second signal is varied or induced by the first signal. 
 
     
     
       2. The method of  claim 1  wherein the filter bank includes at least one filter circuit. 
     
     
       3. The method of  claim 1  wherein at the filter bank includes at least one bandpass filter. 
     
     
       4. The method of  claim 1  wherein the measurement of time varying harmonic distortion includes measuring time varying harmonic distortion at one or more frequencies. 
     
     
       5. The method of  claim 4  wherein the measuring of time varying harmonic distortion at one or more frequencies includes measuring, the time varying harmonic distortion simultaneously. 
     
     
       6. The method of  claim 1  further comprising coupling one of the output terminals of the filter bank to a phase and or frequency modulation demodulator to measure phase and or frequency modulation from one or more time varying harmonic distortion signals. 
     
     
       7. The method of  claim 1  further comprising measuring from time varying amplitude, differential gain, and or differential phase of one or more time varying harmonic distortion signals. 
     
     
       8. The method of  claim 1  wherein the second signal comprises two or more signals. 
     
     
       9. The method of  claim 8  further comprising measuring from at least one output of the filter bank phase and or frequency modulation from at least one harmonic distortion signal, and or measuring time varying amplitude, differential gain or differential phase from at least one time varying harmonic distortion signal. 
     
     
       10. An apparatus for measuring in a time domain time varying or dynamic harmonic distortion from an audio device, wherein the audio device has an input and an output, comprising;
 providing a first signal comprising a pulsed sinusoidal, stairstep, staircase, bipolar, and or arbitrary waveform and a second signal whose frequency is higher than the frequency of the first signal, to an input of the audio device; 
 coupling the output of the audio device to an input of a filter bank, and wherein the filter bank includes at least one output terminal; 
 measuring the time varying harmonic distortion via measuring or displaying the amplitude level from the output terminal of the filter bank to provide the time varying harmonic distortion measurement of the audio device, 
 wherein the time varying harmonic distortion includes a harmonic distortion signal of the second signal, and wherein the harmonic distortion signal of the second signal is varied or induced by the first signal. 
 
     
     
       11. The apparatus of  claim 10  wherein the filter bank includes at least one filter circuit. 
     
     
       12. The apparatus of  claim 10  wherein at the filter bank includes at least one bandpass filter. 
     
     
       13. The apparatus of  claim 10  wherein the measurement of time varying harmonic distortion includes measuring time varying harmonic distortion at one or more frequencies. 
     
     
       14. The apparatus of  claim 13  wherein the measuring of time varying harmonic distortion at one or more frequencies includes measuring the time varying harmonic distortion simultaneously. 
     
     
       15. The apparatus of  claim 10  further comprising coupling one of the output terminals of the filter bank to a phase and or frequency modulation demodulator to measure phase and frequency modulation from one or more time varying harmonic distortion signals. 
     
     
       16. The apparatus of  claim 10  further comprising measuring from time varying amplitude, differential gain, and or differential phase of one or more time varying harmonic distortion signals. 
     
     
       17. The apparatus of  claim 10  wherein the second signal comprises two or more signals. 
     
     
       18. The apparatus of  claim 17  further comprising measuring from at least one output of the filter bank phase and or frequency modulation from at least one time varying harmonic distortion signal, and or measuring time varying amplitude, differential gain or differential phase from at least one time varying harmonic distortion signal. 
     
     
       19. An apparatus for measuring in a time domain time varying intermodulation distortion from an audio device, wherein the audio device has an input and an output, comprising;
 providing the first signal and the second signal and including a third signal whose frequency is different from the frequency of the second signal, wherein the second, and third signals are higher in frequency than the frequency of the first signal, 
 coupling the first, second, and third signals to an input of the audio device; 
 coupling the output of the audio device to an input of a filter bank, and wherein the filter bank includes at least one filter and at least one output terminal; 
 measuring the time varying intermodulation distortion via measuring or displaying the amplitude level from the output terminal of the filter bank to provide the time varying intermodulation distortion measurement of the audio device,
 wherein the time varying intermodulation distortion measurement includes measuring an intermodulation distortion signal of the second and the third signals, and wherein the time varying intermodulation distortion signal is varied or induced in time by the first signal. 
 
 
     
     
       20. The apparatus of  claim 19  further comprising coupling one of the output terminals of the filter bank to a phase and or frequency modulation demodulator to measure phase and frequency modulation from one or more time varying intermodulation distortion signals.