Calibrating the SPL input has two stages: the first is to adjust
the soundcard's input volume control so that there is sufficient
headroom to properly capture peaks in the response whilst having
sufficient signal level to get clean measurements - the target is for
the RMS reading on the input to be around -18dB when a speaker
calibration signal is played.
The second is to give the Wizard an absolute SPL reference by entering a
reading from your SPL meter while a speaker or subwoofer
calibration signal is playing. Note that the
Measurement Level must be set
before setting the input volume.
- The selected soundcard input must be connected to the
meter's analogue output, see
Getting Started for
leads/adaptors that may be required
- Set your SPL meter to C weighting and set the range to suit
the Measurement Level (the 80dB range is recommended
for the Radio Shack meter)
- Press the Set Input Volume button
- Follow the on-screen instructions and wait for the volume setting
to complete
- The text on the Set Input Volume button is
shown in red until volume setting has been carried out. A warning is
shown if measurements are made before setting the input volume and
calibrating the SPL reading as the results of the measurement would
not reflect the actual SPL. The SPL reading is shown in red
until the input volume setting and SPL calibration procedures have been
completed
- The input volume only needs to be set once, do not repeat for
each speaker
- The wizard remembers the input volume setting for the next startup,
so it will usually not be necessary to repeat this process, but check the
Wizard SPL reading against your SPL meter before starting a new set
of measurements
- If the input volume setting is changed or another soundcard input is
selected it will be necessary to repeat the volume setting process
(selecting a different input or input device will cause the Wizard to
show the SPL reading as uncalibrated - the reading changes to red).
- If the name of the volume control is not the standard Windows
settings (volume) the name the soundcard driver uses can be chosen
from the Soundcard menu -
setting the input volume should be repeated after doing that
- The Wizard automatically de-selects all other inputs when it
starts up, it should not be necessary to make any manual selections
in the Windows mixer (This only happens if an
input has been chosen from the "Choose input..." list).
- Changes in volume settings outside the wizard (e.g. in the
Windows mixer) are automatically detected and reflected in the wizard's
controls
- Some soundcards do not provide an input volume control (e.g.
some USB cards). As long as the signal RMS level is within the -30 to -12dB
range when the speaker/subwoofer cal signal is playing everything
should work OK. If the level is below -30dB try reducing the meter range
to raise the level, but be careful not to reduce the range to the point
the meter is overloaded. If the level is above -12dB try increasing the
meter range to lower the level.
- Some soundcards do not provide programmatic access to their input
volume control so the Wizard may not find a volume control or it may
not be able to alter it. In that case you can use the controls in the
soundcard's mixer to make the required adjustments manually: turn on the
Wizards's SPL meter whilst the speaker/subwoofer cal signal is playing
and adjust the volume control in the soundcard's mixer to get
the displayed input level as close to -18dB as you can.
- On some soundcards the wizard may not be able to directly select
the required input via its device and input selectors - for example, on
Audigy 2 selecting the Line In is done by selecting "Analog Mix" in the
Record panel of the Basic tab of the Creative Surround Mixer then going
to the Source panel and muting all the sources except for Line In. If
it does not seem possible to select the required input via the Wizard's
device and input selectors, or the Wizard does not seem to be making
the correct setings, set the input device only, leave the input
unselected (showing "Choose input...") and make the input selection and
input volume adjustments via the soundcard's mixer. An example of suitable
Windows volume control settings is shown below, with Line In selected

- Unfortunately the Wizard is a bit clunky on the Mac, Apple have
their own class library for accessing the audio hardware and provide
only very limited support for the core JavaSound implementation. If
you set the sampling rate to 44.1k in the Soundcard menu you should
be able to choose Mac OS X Core Audio as the input device. Set the
input volume by using the level tweaking tool in the Mac's Sound
Preferences as there is no programmatic access for the Wizard.
Once the input volume has been set the Wizard's SPL Meter reading
needs to be calibrated against your SPL meter.
- Turn off the Signal Generator if it is running
- Press the Calibrate button below the SPL reading and follow the
on-screen instructions
- Enter the reading from your SPL meter and press Done
The wizard remembers the SPL calibration for the next startup,
so it will usually not be necessary to repeat this process, but check the
Wizard SPL reading against your SPL meter before starting a new set of measurements
Having set the measurement level, the Wizard is ready to
calibrate the soundcard.
Help Index
Room EQ Wizard homepage