Filter Adjustment

Having obtained a set of measurement data for a channel it is time to adjust the EQ filters to counter the effects of resonances. Before starting this, establish communications with the equaliser or TAG McLaren AV processor as explained below (you can skip this step if entering filter settings manually).

Communicating with a TAG McLaren AV Processor

The wizard can communicate with AV32R or AV192R processors to retrieve and send settings (see Communicating with AV32R DP or AV192R). Select the COM port in the Comms menu and connect to the AV processor using the programming lead. If using the rear panel connections, plug the black lead into the "out" socket. Do not connect the red lead.

Backup TAG McLaren AV Processor Settings

Before proceeding further it is advisable to back up the settings in your AV32R DP or AV192R using the TMA User Settings Backup utility.

Read Speaker Settings

Use the Read Loudspeaker Configuration from Unit (Ctrl+R) entry in the Equaliser menu to retrieve the processor's speaker settings. Alternatively, enter the speaker type and cutoff frequency for each channel manually in the Filter Panel.

Read and Save Current Filter Settings

Use the Read Channel Filter Settings from Unit (Ctrl+F) entry in the Equaliser menu, selecting All channels, to retrieve the current TMREQ filter settings from the processor then save them as a .req file using the Save Filter Settings entry in the File menu.

Communicating with a BFD Pro

The wizard can communicate with a BFD Pro via a Midi interface to send filter settings (see Communicating with the BFD Pro). Select the Midi ports in the Comms menu and connect to the BFD Pro using the Midi interface.

Adjusting Filter Settings

The sample data below will be used to provide an example. The blue curve is the Target Response.

Sample Measurement Data

Find the Peaks

First we need to locate the peaks in the measurement. For this we use the Find Peaks button in the control panel, which searches within the frequency range defined by the controls below the button.
Find Peaks

If the Target Level has been set during the measurement process then the Target Response will be at the correct level to act as a reference for identifying the peaks. If not, the level should be set before proceeding, either via the Set Target Level button in the control panel or by manually adjusting the level in the Filter Panel until the target response appears to be at the level this channel would have without the influence of the peaks and dips contributed by the room. The default target shape is a flat line at the Target Level, alternative shapes may be specified by loading a House Curve data file.

Find Peaks comes up with the following results:

        Pk   dB    Hz
         1  18.3 129.0
         2  15.4  36.7
         3   4.6  99.0
        

Assign Correction Filters

The next step is to use the Assign Filters button to configure peaking filters to counter the resonances that produce the peaks. The results of that inital assignment are shown below, the corrected trace (light red) shows the predicted effect of the filters. The filter numbers are shown along the top of the graph. The Invert Filters option has been used to draw the filter responses inverted to more easily see their match to the peaks they are assigned to correct.

Initial Assignment of Filters

Initial Assignment of Filters

Before starting the filter optimisation the centre frequencies should be compared to the measurements and adjusted if necessary - the Wizard rounds the filter frequencies to the nearest frequency the equaliser supports and makes allowance for characteristics of the response that may indicate that the resonance is actually offset slightly compared to the position of the peak on the graph, but this may result in a centre frequency a little higher or lower than ideal.

Optimise the Filter Settings

Next Optimise PK Gain and Q is used to adjust the filter settings to bring the Corrected trace closer to the Target Response. Here are the results:

Result of Optimising Filters

Filter Settings after Optimisation

An additional filter has been used for the peak at 129Hz because it is too large to be corrected with the maximum 15dB attenuation of a single TMREQ filter and the Allow doubled filters option is selected. This is useful for pulling down the level of a very large peak, but using two filters often does not achieve as good a match to the shape of a peak. For comparison, here is the result when a single filter is used at 129Hz:

Without doubled filters

The level now sits above the target, but is flatter through that region.

Note the following:

Manually Tweak Settings as Required

The filter settings can be manually adjusted to improve the correction, typically adjusting the Q values and using the Adjust PK Gains button to readjust the gains to suit. The graph traces update as the adjustments are made making the process fast and easy. In the following plot the Q of filter 4 has been reduced to flatten the response around 129Hz and the Q of the 37Hz filter has been increased.

Result of Manually Tweaking Filters

Filter Settings after Manual Tweaking

Transfer the Settings to the Equaliser

Having arrived at a set of filters to use for this channel, they can be transferred to the AV processor or equaliser (e.g. BFD Pro) using the Send Filter Settings to Equaliser (Ctrl+Shift+F) entry in the Equaliser menu. Note: This will overwrite any existing filter settings for the channel. The channel can then be re-measured with the filters active to check the effect they have had, or you can move on to measuring and correcting the next channel.

Notes

  1. After applying correction filters it may be necessary to adjust the speaker calibration for the channel that has been corrected as removing resonant peaks will reduce the overall SPL. This is almost always necesary for the subwoofer, but less so for the other channels if the corrections are all below 200Hz. Carry out the normal speaker calibration using your AV processor's internal test tones.
  2. Repeating the Set Target Level process after applying correction filters can give a more accurate figure, especially for the subwoofer. That new Target Level can be used with the original measured data to repeat the process of finding peaks and adjusting filters, which will typically result in slightly different gains and bandwidths for the corrections.
  3. Filters which are disabled will download to the BFD Pro DSP1124P with their frequency, gain and bandwidth settings as configured, but the filter mode will be set to off (OF) rather than parametric (PA). On FBQ2496 the gain will be set to zero.
  4. Downloading a set of filters to DSP1124P takes about 5 seconds, downloading to FBQ2496 takes about 1 second per filter, 20 seconds for the full set.

Save the Settings

Once you have arrived at filter settings for all channels it is advisable to use Save Filter Settings to store them as a .req file. Note that this saves the settings for all channels in a single file.

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