Tone and White Noise Results using the DSP card


Purpose:

  1. Prove that the Software (NLMS algorithm and card interface) and the Hardware (SHARC Ez-Kit Lite) can combine to actually cancel noise
  2. Give before and after results for the ANC at the testbed


Procedure

  1. For tone, the set-up is a signal generator set for 500 Hz feeding into the DSP card. One speaker outputs the signal, the other speaker outputs the cancelation signal. The other input is the error microphone.
  2. For white noise, the DSP card generated a random number all other elements were the same as the tone set-up.
  3. These elements are in a rough line of 8 feet at the Half Moon Bay test bed.
  4. The adapt software is downloaded to the DSP card and run.
  5. The 800th to 2800th error samples are saved to a datafile on a host PC
  6. These files are then displayed and analyzed using the CoolEdit tool.
  7. The NLMS algorithm was used running 32 taps and a stability constant of 0.2
Tone Results
Time Domain Frequency Domain
Baseline Calibration time domain Calibration Frequency
Initial Result Initial result good out freq
Improved Performance Result good output 14 good output 14 freq


Results

The calibration has the 500 Hz tone at -18 dB.
The initial result has the tone at -28 dB
The result with improved processing performance has the tone at -48 dB.

In all cases the ANC provided significant noise reduction. In most cases the system became unstable in the timeframe of ten's of seconds to several minutes.

White noise initial results
Time Domain
Baseline white noise calibration
ANC white noise ANC


Results


We haven't been able to get the white noise version to converge yet. Work is still ongoing.

Questions?


dak 1/11/98