10
Mackie Industrial White Paper
Noise Sensing
September 2000
3.6 Factory Restore
If you nd that the EEPROM is corrupted or has not been ini-
tialized from the factory, you can perform a
Factory Restore
upon installing the SP-DSP1™ and running the SP-Control™
application.
A new SP-DSP© card should have all parameters
of all presets set to default values (see Table 1).
3.7 Upload/Download From/To EEPROM
Occasionally, it is necessary to backup SP-DSP1™ presets and
parameters or to transfer settings from one DSP to another.
To copy the contents of the EEPROM, simply
Connect
to
the DSP card and then select
Upload From EEPROM.
The
EEPROM contents are stored in your Palm™. If you would
like to copy contents of the Palm™ into another SP-DSP1™
card, select the
Download To EEPROM.
Be advised that this
will completely erase the existing contents of the EEPROM
and replace with what was uploaded to the Palm™. Be careful
to do an
Upload From EEPROM
before
the
Download To
EEPROM
to ensure that valid data exists in the Palm™.
4 Tips for Setting User Parameters
To clarify, setting the user parameters (
MG, GR, NT, NR,
Attack Time and Release Time
) can be done either before or
after the
Auto Calibration
. These parameters have no bearing
on the calibration and can be changed at any point. In fact, a
Preset Save
and
Recall
only affect these parameters.
The
Auto Calibration
only concerns itself with the Calibration
or
CAL
value and the adaptation coefcients. The user param-
eters can be set up for runaway gain, but the user would
notice this immediately as the system would “runaway” to
the maximum gain. During calibration, the user parameters
are temporarily overridden to perform the calibration at a
xed gain (easier and better results). However, the xed gain
used during the calibration process is the Maximum Gain
(
Minimum Gain + Gain Range
). It is probably advisable for
the user to set up these two parameters so that he isn’t “blown
away” by the calibration sequence if his Maximum Gain is
louder than he intends. The Maximum Gain is used as the
calibration value because the algorithm adapts more quickly
when the music is loud. The calibration itself doesn’t limit
the parameters the user can adjust in any way, it just provides
a ‘hidden override’ when he has his
Noise Threshold
set too
sensitive, which would otherwise cause runaway. You’ll notice
that once your unit has been calibrated you can set the
Noise
Threshold
as low as you want and you will still seem to get
the same sensitivity. This is because it is being limited by the
Noise Threshold Override (see Figure 1).
As you can see, one of the rst questions that the end-user
needs to answer is “How much overall system gain or attenua-
tion do you want the noise sensor to provide?” By answering
this question you have determined the setting of the
Gain
Range
(
GR
). A typical good starting point for the Gai
n
Range
is about 20dB. If you nd the system does not attenu-
ate enough or attenuates too much, adjust accordingly. By
answering this rst question, you are likely to determine the
Minimum Gain
(
MG
) as well. Since the average user would
want his system to attenuate from the unity point (0dB),
which is the highest sound level he would ever want, for
this example the
Minimum Gain
would be set to –20dB. As
mentioned in Section 3.1 User Parameters (Sliders), by setting
the
Minimum Gain
and the second parameter,
Gain Range
,
you are actually establishing the program operating window
within which the levels for the program material must remain.
As in the previous example, if the user wanted his music levels
to operate in a range
±
10dB around -10dB down from the
input level (unity point), he would set
MG
=-20dB and
GR
=20.
Setting the
Noise Threshold
(
NT
) can only be done by deter-
mining the noise level at which you want the music to start
to increase in level. This noise threshold point is best found
through trial and error. You must be careful not to set the
NT
too low (i.e. more negative), because the noise sensor will
begin “gaining up” the program material with very little noise.
However, setting the
NT
too high will prevent the system from
making any program gain increases until there is a relatively
high noise level. There is a balance and each room will require
a different
NT
setting. Keep in mind that setting this level in
an empty room may require some “tweaks” when the room
is full with people. For example, if you set
NT
=-40dB in an
empty restaurant, you may nd that the system starts gaining
up too fast and is too loud for the occasion. In this case, you
can reduce
NT
(by bringing the level closer to 0dB) by 5 to
10dB. This would give you
NT
=-30 to -35dB and the system
would not start “gaining up” until the noise was 10dB “hotter”
than it was previously.
Noise Range
(
NR
) actually sets the amount of noise that makes
the program gain go from the minimum setting to the maxi-
mum setting. That is, if
NR
=40dB and
GR
=20dB, then for
every 2dB change in the Noise, the Program level is only
