HBA09-001-70
HB-NEDSP1068
8
Check to make sure that the audio is clear and distortion free.
If there seems to be some spitting or distortion heard under sudden loud noises, then
consider adjusting P2 (Audio in) again, counter clockwise very slightly and re-check
under the same conditions.
If you have an oscilloscope to hand you can check the audio levels at the output and at
the junction of R3/C13 (see page 11 for the top side of the PCB layout). The signal at
this point should be no more than 2.0 V p-p maximum. Failure to observe this level can
lead to the DSP IC shutting down, this then requires power to be removed from the
board and then re-applied to cause a reset.
Alternatively, probe the wiper of P2 (Audio in) and check that the signal doesn’t peak
over 625mV peak/1.25volts p-p. This will ensure that the output signal won’t spit on
peaks or cause the DSP device to shut down until power is removed and re-applied.
6.1.9 Noise cancelling settings
Jumpers J5 through to J7 select the level of noise cancellation (see the table below).
For most operations level 4 is quite adequate, but for more severe conditions, the level
may be increased to 5, 6 or 7.
It will be found that under certain high noise conditions, and with poor speech quality,
levels 7 and 8 can cause the audio quality to be rather mechanical with musical tones
being present with the audio. This may be an acceptable trade off because as you may
now be able to clearly hear the speech, whereas before the high noise prevented this.
To inhibit the noise cancelling algorithm completely, pin 8 of J2 should be grounded.
Audio will be passed through un-processed. It is recommended that a switch be fitted to
perform this function, so that you can check the audio quality and the filter performance.
Level Tone
Reduction
(dB)
White Noise
Reduction (dB)
N0 N1 N2
1 4
9 X
X
X
2 5
11 -
X
X
3 6
13 X
-
X
4 8
15 -
-
X
5 16
17 X
X
-
6 21
20
-
X
-
7 25
24 X
-
-
8 65
35
-
-
-
X – Jumpers require fitting to obtain the filter level. Remove all jumpers if the module is
to be used with an external controller or via J2 pins 1, 2, 3 and 8.
