REW can work with data you have already acquired by manual measurement or using another program (see Importing Measurement Data), or it can act as a complete signal generation, data capture/analysis and filter tuning tool. This section gives an overview of getting REW running as a complete solution for room response measurement and equalisation filter tuning, if you already have some data you want to tune filters against you can import it and skip to Filter Adjustment.
When using REW to make measurements it is best to exit any other applications, disconnect from the internet and disable any wireless networking. Interference on audio inputs from the wireless interface or high processor demand from other applications, anti-virus updates and the like can cause gaps in the generated or captured audio signals leading to incorrect measurement results.
The steps required to make room measurements are:
If running REW for the first time it is best to read through these initial help chapters in sequence rather than jumping directly to the individual setup steps, however if your computer has already been set up using other acoustic measurement software you may be able to skip directly to Making Measurements.
Measurements may be made by connecting directly to an equaliser
or by connecting to an AV processor input. If your aim is solely to
configure an equaliser (such as BFD Pro DSP1124P or FBQ2496) to optimise
your subwoofer's response, connect one of the soundcard's line outputs
directly to the equaliser input in place of the Sub connection from your
AV processor. For a BFD Pro the operating level switches on the rear
panel should be pressed in to select the -10dBV range.
To make measurements that will show the response of main speakers as well as the subwoofer, and to view the integration between subwoofer and main speakers, connect to an AV processor input so that the effects of your AV processor's bass management can be included in the measurements. Connecting to the left or right channel of an analog input will allow the corresponding main speaker and the subwoofer responses to be measured - turn off or disconnect the relevant main speaker or the sub to exclude them from a measurement.
AV32R DP and AV192R allow the test signal input to be routed to any speaker output via the Test Signal entry within the TMREQ filter menus for each speaker, which is handy for measuring other speakers (see this note for details). They seem to be the only AV processors with such a facility, other processor may have 5.1 or 7.1 analog inputs that can be used to similar effect, but in some cases bass management will not be applied to such inputs, limiting the ability to check sub/main speaker integration.
To measure the responses of individual speakers and subwoofer in the
absence of 5.1 or 7.1 inputs it may be possible to connect the soundcard's
line output directly to the line level input of the amplifier driving
the corresponding speaker, in place of the connection from the AV processor
- however if connecting directly to the
amplifiers great care must be taken to ensure that high signal levels are
not inadvertently presented as this could damage loudspeaker drive
units.
If the AV processor input being used has an anti-clipping feature (automatically reducing its sensitivity if it detects large signals) this should be turned off, as it could shift the measurement levels. The sensitivity of the input should ideally be set to 0.5V, though this is not critical.
Your SPL meter's range should be set to the value normally used for speaker level calibration and must not be altered while using REW. If you are using the Radio Shack meter, select the 80dB range if you calibrate your system at 75dB (this is the standard level recommended by DolbyTM).
Set your meter to C weighting. If you are using a microphone and preamplifier for measurement, untick the C Weighted SPL Meter box in the Mic/Meter Settings.
REW defaults to using the audio input and output which have been set as the defaults in your OS. If you wish to use other audio inputs or outputs they can be selected in the Soundcard Settings panel, click the Settings button in the toolbar to display the panel. The device lists show all soundcards that REW has detected, when a soundcard has been selected the input and output lists show the available inputs/outputs on that soundcard. Note that if a USB soundcard is plugged in after REW has been started it may take up to 1 minute for it to appear in the list of devices - this is a feature of the Java Runtime Environment.
The lists include both internal and external devices and default drivers
offered by the operating system.
Where possible, select the soundcard itself rather than the OS drivers "Primary Sound Capture Driver", "Primary Sound Driver", "Java Sound Audio Engine" or similar. REW needs direct access to the controls on the soundcard if it is to automatically adjust levels, this may not be possible if the OS drivers are selected.
Once the devices have been chosen, the input and output can be selected. Typically the input will be called "LINE_IN" and the output will be "SPEAKER" or "LINE_OUT", however these names may be different for USB soundcards - for example, the input may be labelled "Digital Audio Interface".
Trouble-shooting tip: To prevent REW from accessing soundcard controls, leave the input and output devices set to "Default Device". The actual input and output used and any level control settings will then need to be made using the OS volume controls and/or the soundcard's mixer.
Note that on a Mac it may be necessary to set the Sample Rate to 44.1k to access audio inputs and outputs. There is no programmatic access to soundcard controls on the Mac, use the controls in Applications - Utilities - Audio Midi Setup.
After the inputs and outputs have been selected the next task is to Calibrate the soundcard.