Filter design

The Filter Design screen

Once the full set of measurements has successfully been taken, Dirac Live has the acoustical information it needs about your loudspeakers and listening room to create the correction filters.

Frequency response display

The Filter Design tab shows -- by default --the average measured response of the left front speaker (mauve line) and the target curve (yellow/black line):

Note: the graph as shown is the default initial display. The "curtains" at about 95 Hz and 1.5 kHz are the automatically detected range of correction. These are incorrect because they include all speakers including some small speakers (so Dirac Live sets the low frequency limit too high) and the subwoofer (so Dirac Live sets the high frequency limit too low).

You will want to:

1. Create groups for each type of speaker, and

2. Change the curtains to be more appropriate for each group.

Channel selection and groups

By default, there is one group for all channels. This means that one target curve and frequency correction range will apply to all channels.

Click on the individual channel names to display the response graphs of that channel, or on the group name to display the response graphs for all channels in that group. To display a selection of channels within a group, hold the Control button (Windows) or Command key (macOS) while clicking on the channel names.

For most multichannel applications, you will need more than one group. To separate a channel into a different group, click on the channel name and drag it out of the group box. There will then be two groups. Drag other channels into the new group, or drag channels into the blank space to create another new group.

Here is a typical example for home theater, with groups for the two front channels, the subwoofer, the center, and four surrounds:

To display the graphs of multiple groups, hold the Control button (Windows) or Command key (macOS) while clicking on the group names.

Range curtains

The grey regions to the left and right of the graph are excluded from magnitude correction. You can adjust the frequency range of correction by dragging the "curtains" to either side of the graph. There is a separate pair of range curtains for each group.

By default, Dirac Live sets the range curtains to the detected range of all speakers. The detected range is shown as a pair of vertical dotted lines. After splitting the speakers (and subwoofer) into multiple groups, set the range curtains of each group.

• Avoid setting the low frequency curtain too low, as this can result in excessive boost and increase distortion.
• The high frequency curtain can be set where you like. We recommend trying a full-range correction for at least one of your profiles. Or, if you are happy with the inherent in-room response at higher frequencies, try setting the upper curtain to limit correction to the modal region (up to 300 Hz, in a typical room). Be careful not to allow the speakers to differ too much at higher frequencies, as this can result in audible changes in the soundstage.

Display controls

There are several controls at the right of the graph:

Spectrum

Display the average of all magnitude responses. If the "Measured" checkbox on the left is on, the average of the uncorrected measurements is displayed. If the "Corrected" checkbox on the right is on, the average of the response after correction is displayed.

Group colors

If checked, the graph colors are the same for all channels in a group. This can be individually selected for the measured and corrected responses. This is useful when displaying the responses of multiple groups.

Spread

Display the responses at all measurement locations as a lighter highlight on the graph. This can be individually selected for the measured and corrected responses. This example shows the spread of responses after correction:

Target curve

Display the target curve for the current group or groups.

Curtains

Display the correction frequency range for the current group or groups. This is shown as "curtains" to the left and right of the graph.

Detected Range

Display two vertical cursors indicating the frequency range within which Dirac Live has determined the speakers of the current group to have reasonable output. Note: at low frequencies, environmental noise can cause this estimate to be incorrect.

Zooming in on the graph

The graph can be zoomed in and out by using the mouse wheel, or with zooming gestures on a touchscreen or touchpad. To move a zoomed graph, left-click and drag with the mouse, or use the grab and move gesture with a touchscreen. To zoom out to 100%, double-click on the graph or right-click and select Reset zoom.

Adjusting the target curve

The target curve is the response you desire from the speakers after correction. This will be an average of different locations around the listening area.

Using the shelving controls

By default, the target curve provides two controls: bass shelf and treble roll-off. Simply grab and drag the horizontal lines to move the level of the bass shelf or degree of treble roff-off or boost. The bass shelf ranges from 0 to +12 dB, while the treble control ranges from -3 to +4 dB.

Editing with control points

If the shelving filters don't provide enough control you can switch to using control points with the icons located with each group on the right side of the window:

The control points are shown as dots on the target curve, which can be used to edit the target curve as shown here:

Converting shelving filters to control points

The target curve with shelving filters and the target curve with control points are stored separately, and you can switch back and forth between them. The default target curve with control points is a straight line with a slight downward tilt:

If you would prefer to start with the same shape as the shelving filters, click the icon to view the shelving filter, then right-click on the graph and select Convert shelves to control points:

The shape of the target curve with control points will now be the same as the shelving filters, and you can edit further as described above:

Snapshots

You can save the current set of groups, target curves and curtain frequencies by clicking on the Take snapshot button:

Snapshots will by default be named as the current time. They can be renamed for easier selection later on. Click on the right side of the button and then on the pencil-shaped icon. Enter the name and press the Enter key:

To select a saved snapshot, click on the right side of the button and then click on the desired snapshot.

To delete a saved snapshot, click on the right side of the button and then click on the "x" icon.

Reset to default

To reset a target curve and the range curtains to the default, drop down the menu from the hamburger icon and select Set default target curve, then select the group to reset:

Saving and loading individual target curves

Target curves can be saved and loaded individually for use at a later time or in other projects. To save a target curve, drop down the menu from the hamburger icon and select Save target curve, then select the group:

To load a target curve, drop down the menu from the hamburger icon and select Load target curve, then select the group:

Guidelines for target curve design

Care should be taken to create a target curve that works well with your speakers and room, as well as suiting your personal preferences. Small changes to the target curve can have significant effects on the tonal quality of the system, so it is important that you experiment with different target curves.

If you initially don't achieve a satisfactory result, ensure that you have spread your measurements over a sufficiently large area and with sufficient variation in height. The following guidelines will help you understand how to adjust your target curve.

Low-frequency extension and boost

All loudspeakers have a natural low frequency roll off. Setting the target curve to boost the region below the speaker's natural roll off frequency may result in overdriving the speakers, especially with smaller home loudspeakers and depending on your listening habits. A system with capable subwoofers integrated into it, however, will support much more low-frequency output.

High-frequency "tilt"

The target curve is the desired measured response of loudspeakers in a room, in contrast to measurements made of a loudspeaker during its design under anechoic (measured in free space) conditions. While high-quality loudspeakers are usually designed for a flat on-axis anechoic response, these same speakers when placed into a listening room will tend to have a downward-sloping or "tilting" response at high frequencies, due to the effects of limited dispersion at high frequencies and greater acoustic absorption.

A completely flat in-room response is therefore usually not desirable and will tend to sound thin or bright. Start with a target curve that follows the natural behavior of your speakers in your room, and then experiment with greater or lesser degrees of tilt in the treble region to obtain the most natural timbral balance.

Low-frequency adjustment

A completely flat response at low frequencies, with complete elimination of peaks due to room modes, may sound light in the bass. Typically, a slight increase in the target curve below 100 Hz will give a more balanced sound.

Magnitude response dips

In some cases, it may be helpful to adjust the target curve to follow dips in the measured response. This can occur where, for example, the listening area is very close to the speakers and the measurements exhibit a dip caused by the vertical response of the speakers themselves. Experiment with a target curve that follows the dips. You may also wish to try a different set of measurement positions.

Ungrouping left and right channels

Usually, each pair of corresponding left and right channels (front left and right, surround left and right, and rear left and right) should be in the same group for target curve adjustment, to ensure that both sides produce the same response across the listening area. In certain unusual circumstances, such as where the magnitude response dip discussed above shows up on only one side, you can try ungrouping channels and making separate adjustments.

The Impulse response graph

The Filter Design menu can be used to display the impulse response:

Example impulse response

Below is an example impulse response display. This example shows the original impulse response at the top and the corrected and delayed impulse response below.

Impulse response controls

There are several controls at the right of the graph:

Impulse response

Display the impulse response corresponding to the average of all magnitude responses. If the "Measured" checkbox on the left is on, the impulse response corresponding to the measurements is displayed. If the "Corrected" checkbox on the right is on, the impulse response corresponding to the corrected response is displayed.

Group colors

If checked, the graph colors are the same for all channels in a group. This can be individually selected for the measured and corrected impulse responses.

Show latency

Show the corrected impulse responses on a time scale that includes processing delay.

Separate curves

Show the measured and corrected responses on separate graphs. See above for an example.

Dense grid

Display additional grid lines on the graph.

Cursors coordinates

Display a vertical cursor line where the mouse is, together with the time delay and impulse response value at the cursor position.