Metric Halo SpectraFoo - Manual (Page 73)

The Transfer Function
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will not disappear. They will make the system sound ragged on the high end and will also make the system
sound phase-y when the listener moves around. These are caused by acoustic reflections and are best treated
with diffusion or absorptive material.
We can now try to correct the system with equalization. What we want to do is adjust the system EQ to match
the inverse of the system response. When we do this, we will pre-compensate the signal sent to the sound
reinforcement system so that when it applies its effective equalization to the signal, the result balances out and
leaves us with a (relatively) flat system response.
System Correction
1. Switch the response signal source to be the output of the system equalizer.
2. In the Overlays window, click the checkbox in the “V” column of the transfer function overlay that
corresponds to the system response that you want to correct. This makes the snapshot visible in the
Transfer Function window. (Make sure that the “I” checkbox is also checked. This Inverts the snapshot
– which makes it look like the EQ curve that we need to correct the system.) The overlay is displayed
in the color of the tile next to the snapshot name. If you want to change this color, click on the tile
and choose the new color.
3. Select Coherence from the Fade pop-up menu of the snapshot in the Overlays window. This will fade
the trace based on the coherence of the measurement. It allows you to see what portions of the response
are equalizable.
4. Start your signal source. Pink noise tends to work best when you are measuring your EQ, because you
don’t have to listen to it. You can still use music if you want to be able to listen to the effects of the
system EQ as you are changing the system EQ.
5. Since there is very little environmental noise in this measurement, you can decrease the setting of the
Avg. Power Cutoff slider.
6. Again since there is very little environmental noise, and since we want to be able to see the changes
in the equalizer response as we change the equalizer settings, you can decrease the setting of the Avg.
Rate slider.
7. Click the Compute Delay… button to recompute the delay for the equalizer. The system will compute
and compensate for the delay through the equalizer. After a few seconds, the coherence curve should
be near the top of the panel for the entire audio range and the power curve should be flat (this assumes
that the EQ has been zeroed out).
8. Move the inverted system response curve so that the highest points on the curve are level with the
live trace. You do this by clicking on the response curve and dragging it vertically until it is positioned
properly. You want to make this adjustment so that you can correct the system using an all-cut EQ curve.
9. Adjust the settings on your system EQ to match the general trends of the inverted system response curve.
Avoid trying to match steep peaks in the inverted system response… especially when the coherence
is very low.
Assuming everything went well your system has been corrected, and should now sound significantly better
than when you started. You can re-measure the system response (now with the system EQ switched in), to
verify that the system has been substantially improved; and of course your ears will also let you know.
There are many other types of measurements you can make with the transfer function measurement system.
Transfer Function Snapshot Overlays Reference
Use the Take Snapshot… button in the Transfer Function window to make a new snapshot from the current
transfer function data.
All other snapshot overlay management is done from the Overlay List window: