Method and apparatus for measuring characteristics of an audio system using a tapered chirp
An apparatus and method for measuring the characteristics of an audio system using a tapered chirp. A starting frequency and an ending frequency for a chirp signal during which the chirp signal has a constant envelope amplitude are determined for the audio system to be measured. An intermediate time duration during which the chirp signal has the constant envelope amplitude is determined for the audio system to be measured. A beginning envelope amplitude taper on time duration is also determined for the audio system to be measured. A chirp signal having the starting frequency, the ending frequency, the intermediate time duration, and the beginning envelope amplitude taper time duration is applied as an input to the audio system to be measured. The resulting output signal from the audio system to be measured is acquired to determine the characteristics of the audio system is acquired. A signal source for generating the chirp signal is provided. A chirp parameter selection mechanism is provided for determining the starting frequency, the ending frequency, the constant envelope amplitude time duration, and the beginning envelope amplitude taper on time duration. A signal acquisition device acquires an output signal from the audio system, and a signal processing device determines one or more response characteristics of the audio system to be measured based on the output signal and the chirp signal. Preferably, the frequency of the chirp signal changes exponentially.
1 . A method for measuring the characteristics of an audio system using a tapered chirp signal, comprising:
determining, for the audio system to be measured, a starting frequency and an ending frequency for a chirp signal during which the chirp signal has a constant envelope amplitude;
determining, for the audio system to be measured, an intermediate time duration during which the chirp signal has the constant envelope amplitude;
determining, for the audio system to be measured, a beginning envelope amplitude taper on time duration;
applying the chirp signal having the starting frequency, the ending frequency, the intermediate time duration, and the beginning envelope amplitude taper on time duration as an input to the audio system to be measured; and
acquiring an output signal from the audio system to be measured to determine the characteristics of the audio system.
2 . The method of claim 1 , further comprising determining a beginning envelope amplitude taper on function and applying the beginning envelope amplitude taper off function for the chirp signal.
3 . The method of claim 2 , further comprising starting the chirp signal at a zero crossing.
4 . The method of claim 3 , further comprising tapering the envelope amplitude of the chirp signal to zero after the intermediate time duration.
5 . The method of claim 1 , further comprising determining an ending envelope amplitude taper off function and applying the ending envelope amplitude taper off function to the chirp signal after the intermediate time duration.
6 . The method of claim 5 , wherein the ending envelope taper off function is a cosine squared function.
7 . The method of claim 6 , further comprising starting the chirp signal at a zero crossing.
8 . The method of claim 1 , further comprising starting the chirp signal at a zero crossing.
7 . The method of claim 1 , wherein the starting frequency, the ending frequency, the intermediate time duration, and the beginning taper time duration are selected, and an onset chirp frequency, final chirp frequency and total chirp duration are determined automatically.
10 . The method of claim 9 , wherein the chirp frequency changes exponentially from the onset of the chirp until the termination of the chirp.
11 . The method of claim 9 , wherein the envelope amplitude taper on function is a cosine squared function.
12 . The method of claim 1 , wherein the chirp frequency changes exponentially from the onset of the chirp until the termination of the chirp.
13 . The method of claim 1 , wherein the envelope amplitude taper function is a cosine squared function.
14 . The method of claim 1 , further comprising determining the frequency response of the audio system based on the output signal.
15 . The method of claim 1 , further comprising determining the harmonic distortion of the audio system based on the output signal.
16 . The method of claim 1 , further comprising determining the phase distortion of the audio system based on the output signal.
17 . The method of claim 1 , further comprising providing a visual display for selecting the starting frequency, the ending frequency, the intermediate time duration and the onset amplitude taper time duration.
18 . An apparatus for measuring the characteristics of an audio system using a tapered chirp signal, comprising:
a signal source for generating a chirp signal to be applied to an input of an audio system, the chirp signal having a starting frequency, an ending frequency, an intermediate time duration during which the envelope amplitude is constant, and a beginning envelope amplitude taper on time duration;
a chirp parameter selection mechanism for determining the starting frequency, the ending frequency, the constant envelope amplitude time duration, and the beginning envelope amplitude taper on time duration;
a signal acquisition device for acquiring an output signal from the audio system to be measured; and
a signal processing device for determining one or more response characteristics of the audio system to be measured based on the output signal and the chirp signal.
19 . The apparatus of claim 18 , wherein the signal generator comprises a digital processor programmed to produce a digital form of the chirp signal and a digital-to-analog converter for converting the digital form of the signal to an analog form thereof for application to an input of the system under test.
20 . The apparatus of claim 18 , wherein the chirp parameter selection mechanism includes a data input mechanism for selecting the starting frequency, the ending frequency, the intermediate amplitude time duration, and the beginning envelope amplitude taper on time duration and for automatically determining therefrom an onset chirp frequency, a total chirp time duration, and an ending chirp time duration.
21 . The apparatus of claim 18 , wherein the signal acquisition device comprises an analog-to-digital converter for converting an analog signal output from the system under test to a digital representation thereof.
22 . The apparatus of claim 18 , wherein the signal source produces a chirp signal whose frequency varies exponentially.
23 . The apparatus of claim 18 , wherein the signal source initiates the chirp signal at zero envelope amplitude.
24 . The apparatus of claim 23 , wherein the signal source initiates the chirp signal at a signal zero crossing.
25 . The apparatus of claim 18 , wherein the signal source tapers the envelope amplitude on according to a cosine squared function.
26 . The apparatus of claim 18 , wherein the signal source initiates the chirp signal at a signal zero crossing.
27 . The apparatus of claim 18 , wherein the signal source tapers the chirp envelope amplitude to zero after the intermediate time duration.
28 . The apparatus of claim 27 , wherein the signal source tapers the envelope amplitude off according to a cosine squared function.
29 . The apparatus of claim 18 , wherein the signal processing device comprises a digital signal processor programmed to compute one or more response characteristics of the system under test.
30 . The apparatus of claim 29 , wherein the digital signal processor is programmed to compute the frequency response of the audio system based on the output signal and the chirp signal.
31 . The apparatus of claim 29 , wherein the digital signal processor is programmed to compute the harmonic distortion of the audio system based on the output signal and the chirp signal.
32 . The apparatus of claim 29 , wherein the digital signal processor is programmed to compute the phase distortion of the audio system based on the output signal and the chirp signal.
33 . The apparatus of claim 18 , further comprising a visual display for selecting the starting frequency, the ending frequency, the constant envelope amplitude time duration, and the beginning envelope amplitude taper on time duration.