Background Noise Measurement from a Repeated Stimulus Measurement System

• US 20160373873A1
• Filed: 06/22/2015
• Published: 12/22/2016
• Est. Priority Date: 06/22/2015
• Status: Active Grant

• Current Assignee: Audyssey Laboratories, Inc.
• Original Assignee: Audyssey Laboratories, Inc.
• Inventors: Clark, Jeffrey
• Granted Patent: US 9,743,206 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04R 2205/024 Positioning of loudspeaker enclosures for spatial sound reproduction
• CPC Class Codes: H04R 29/007 for public address systems public address systems per se H04R27/00
• CPC Class Codes: H04R 3/04 for correcting frequency response
• CPC Class Codes: H04R 3/12 for distributing signals to two or more loudspeakers specially adapted for hearing aids H04R25/407
• CPC Class Codes: H04R 5/02 Spatial or constructional arrangements of loudspeakers
• CPC Class Codes: H04S 7/301 Automatic calibration of stereophonic sound system, e.g. with test microphone
• CPC Class Codes: H04S 7/305 Electronic adaptation of stereophonic audio signals to reverberation of the listening space H04S7/301 takes precedence
• CPC Class Codes: H04S 7/307 Frequency adjustment, e.g. tone control H04S7/301 takes precedence

Abstract

A minimum level for a stimulation signal used in room correction processing is determined by measuring background noise. The stimulation signal is repeated a number of times and resulting responses are recorded. The recording responses are averaged, and the average is subtracted from each recorded response to obtain the backg round noise present in each recorded response. A stimulation signal to background noise ratio is computed from the stimulation signal and background noise and compared to an SNR threshold to determine if the stimulation signal level is sufficient to support the room correction processing. The background noise may be AC hum introduced electronically into the response signal, acoustic noise introduced by AC ventilation systems or noise emitting devices (refrigerators, etc), and it may be structure-born noise introduced by shaking the microphone, e.g. a bus drives by, shaking the floor the microphone is standing on.

Claims

1. A method for providing an adequate signal level in the presence of noise, comprising:

providing a stimulus signal to a system including a transducer;

converting the stimulus signal to at least one electro mechanical transducer signal;

transducing the at least one electro mechanical transducer signal by the transducer to produce a physical output in an environment including background noise;

receiving the physical output and background noise by a second transducer;

recording the received physical output and background noise;

repeating the first four steps several times;

averaging the recordings;

subtracting the average from each recording to obtain a noise measurement for each recording;

determining a Signal to Noise Ratio (SNR) of system using the noise measurement;

determining if the SNR is sufficient to ensure accuracy of the physical output produced by the system;

improve the SNR of the system from the stimulus signal input to the transducer if necessary to provide a sufficiently accurate physical signal;

processing the sufficiently accurate physical signal recording to determine changes to the system which will provide improved physical outputs of the system;

implementing the changes in the system; and

processing input signals by the system to produce improved physical outputs.

2. The method of claim 1, wherein improving the SNR comprises increasing the level of the stimulation signal.

3. The method of claim 1, wherein improving the SNR comprises disabling noise making appliances.

4. The method of claim 1, wherein improving the SNR comprises performing the measurement when background noise is lower.

5. The method of claim 1, wherein improving the SNR comprises stabilizing the second transducer used to record the physical output and the background noise.

6. The method of claim 1, wherein the stimulus signal is designed for measuring complex frequency response of an audio reproduction system.

7. The method of claim 6, wherein the measured complex frequency response is used to determine changes to signal processing to improve at least one of a frequency response and a time response of the reproduction system.

8. The method of claim 6, wherein the measured complex frequency response is used to determine changes to signal processing to compensate for different times required for audio signals from each of at least two speakers to reach a listening position.

9. The method of claim 6, wherein the measured complex frequency response is used to determine changes to signal processing to compensate for different audio signal levels from each of at least two speakers perceived at a listening position.

10. The method of claim 1, wherein the stimulus signals are contiguous.

11. The method of claim 1, wherein the SNR is computed using an RMS noise levels taken over a portion of a frequency spectrum by band-pass filtering.

12. The method of claim 1, wherein the SNR is computed using an RMS noise levels are taken over a portion of the frequency spectrum using a subset of frequency response values from an FFT of the measurement.

13. A method for determining a stimulus signal level for correction processing, comprising:

providing a stimulus signal to an audio system;

converting the stimulus signal to at least one speaker signal;

broadcasting the at least one speaker signal from a corresponding speaker to produce an audio signal in an area including background noise;

recording the broadcasted audio signal and background noise;

repeating the first four steps several times utilizing contiguous stimulation signals;

averaging the recordings of the broadcasted audio signal and background noise;

subtracting the average from each recording to obtain a noise measurement for each recording;

computing a noise level of the noise measurements;

determining a stimulus signal level to the noise level Signal to Noise level (SNR);

improving the SNR if necessary to achieve a minimum SNR to ensure accuracy of signal correction processing;

re-transmitting the stimulus signal;

determining the signal correction processing based on the transmitted stimulation signal;

applying the signal correction processing to an electrical signal;

providing the corrected electrical signal to a transducer; and

transducing the corrected electrical signal to a mechanical operation.

14. The method of claim 13, wherein the noise levels are taken over a portion of a frequency spectrum by band-pass filtering.

15. The method of claim 13, wherein the noise levels are taken over a portion of the frequency spectrum using a subset of frequency response values from an FFT of the measurement.

16. A method for audio system equalization, comprising:

providing a stimulus signal to an audio system;

converting the stimulus signal to at least one speaker signal;

transducing the at least one speaker signal by at least one corresponding speaker to produce an acoustic signal in an area including background noise;

recording the broadcasted acoustic signal and background noise by a microphone;

repeating the first four steps several times utilizing contiguous stimulation signals;

averaging the recorded broadcasted audio signal and background noise;

subtracting the average of the broadcasted audio signal from each recording to obtain the noise for each recording;

computing a Root Mean Squared (RMS) noise level of the noise;

determining a Signal to Noise Ratio (SNR) of system using the RMS noise level;

determining if the SNR is sufficient to ensure accuracy of the audio output produced by the system;

improving the SNR of the system if necessary to obtain a sufficiently accurate recording;

producing the sufficiently accurate recording;

processing the sufficiently accurate recording to determine room equalization processing;

applying the room equalization processing to one of an analog or digital electrical signal; and

transducing the equalized signal to an audio signal.

17. The method of claim 16, wherein improving the SNR comprises increasing the level of the stimulation signal.

18. The method of claim 16, wherein improving the SNR comprises disabling noise making appliances.

19. The method of claim 16, wherein improving the SNR comprises performing the measurement during low traffic times.

20. The method of claim 16, wherein improving the SNR comprises stabilizing a microphone used to record the physical output and the background noise.