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changed by 1dB. A good starting point is to set NR equal to
the GR setting. This would give a 1:1 noise to program level
change and would sufce for the majority of installations.
Remember, The Noise Threshold Override will protect the
system from runaway gain even if the NT and NR are set
incorrectly
5 What to Avoid
Once an Auto Calibration has been performed, a user should
never move or change the speaker-microphone placements. In
fact, any changes (i.e. adding more speakers, moving equip-
ment, signicantly changing the room layout, etc.) should
be avoided. If these changes are required, simply recalibrate
by initiating another Auto Calibration. You may nd that in
environments that change daily (new equipment added, equip-
ment moves, etc.) a periodic recalibration would be benecial.
Any gain adjustments made to the microphone preamp should
be done prior to Auto Calibration. Further-more, all level
changes should be made prior to the DSP card. If the system
gain is changed in any way post DSP card, the noise sensor
perceives this as an acoustic noise disturbance. This is why
the level controls on the SP2400/1200 are before the DSP.
Again, any level changes made after the DSP card (i.e. power
amplier, speakers, between the preamp and power amplier,
etc.) will require a recalibration.
6 HyperTerminal Control of SP-DSP1™
If the user does not own a Palm™ or compatible device, he
can use HyperTerminal available on any PC running Windows
OS. HyperTerminal can control all the parameters previously
mentioned. The null-modem adapter is not necessary as the
9-pin female D-Sub on the front of the SP2400/1200 will
connect directly to a PC COMM Port. Mackie Designs will
provide a one-page protocol at the customer's request.
7 Patent Protection
The basic principles of noise sensing presented in this paper
are the subject of patent applications.
September 2000
8 References
[1] Antoniou, A., 1993, Digital Filters: Analysis, Design, and
Applications, 2
ed., McGraw Hill.
nd
[2] Cowen, C. F. N. and P. M. Grant, 1985, Adaptive Filters,
Englewood Cliffs, NJ: Prentice Hall.
[3] Franklin G. F. and J. D. Powell, 1981, Digital Control of
Dynamic Systems, Reading MA: Addison-Wesley.
[4] Haykin, S., 1986, Adaptive Filter Theory, Englewood
Cliffs, NJ: Prentice Hall.
[5] Haykin, S., 1989, Modern Filters, New York: Macmillan.
[6] Hellman, Zwislocki, September 1964, "Loudness Function
of a 1000-cps Tone in the Presence of a Masking Noise",
Journal of the Acoustical Society of America, v. 36, no. 9, pp.
1618-1627
[7] Morzingo R. A. and T. W. Miller, 1980, Introduction to
Adaptive Arrays, New York: Wiley.
[8] Proakis, J. G. and D.G. Manolakis, 1988, Introduction to
Digital Signal Processing, New York: Macmillan.
[9] Proakis, J. G., 1989, Digital Communications, Chapter 6,
McGraw Hill.
[10] Sondhi, M. M. and D. A. Berkley, August 1980, "Silenc-
ing echoes on the telephone network", Proceedings of the
IEEE, v. 68, no. 8, pp. 948-963.
[11] Treichler, C. R., J. R. Johnson, and M. G. Larimore, 1987,
Theory and Design of Adaptive Filters, New York: Wiley.
[12] Widrow, B. and S. D. Stearns, 1985, Adaptive Signal
Processing, Englewood Cliffs, NJ: Prentice Hall.
Noise Sensing
11
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