FIR Designer M : Channels – FIR Auto Mag

This view is the third of five views used to create the channel FIR filter. Responses from all five views are combined or “convolved” into a single FIR filter which is then truncated and windowed on the channel Export tab.

Frequency bands of automatic filtering can be used to shape the loudspeaker response and bring it closer to the target. In each band, the loudspeaker response (after filtering from preceding tabs) is smoothed and the inverted response used as a filter. (The number of bands is unlimited.)

At the frequency edges of each band, a fade-in and fade-out from 0 dB, is applied. When the edges of two bands come within the octave smoothing distance from either band, a cross-fade is applied between the two bands.

The blue line in the upper plot shows the loudspeaker magnitude response – after filtering from preceding tabs – subtracted from the channel target magnitude response.

The aim is to use auto mag bands to match the green line – the filtering for this tab – to the blue line. When closely matched, the loudspeaker response – after filtering – will be closer to the channel target.

Smoothing: Complex or Mag When set to Complex, the loudspeaker response smoothing (used to create the inverted response filter) uses full complex data. When set to Mag, magnitude the smoothing uses the magnitude of the spectral data. Note: Power smoothing could also be done here. This may be included in a future update.
Use Coherence When checked, if coherence is available (from the imported loudspeaker measurement), the coherence is used in the smoothing process to weight spectral values with higher coherence. Thus spectral values with higher coherence have more influence on the smoothed result.
Phase: Minimum or Linear When set to Minimum, the a minimum-phase filter is created from the combined Auto Mag magnitude response. When set to Linear, the phase of the Auto Mag response is 0 degrees.

Auto Mag Response

This plot shows the magnitude and phase for all preceding tabs up to, and including, the Auto Mag, applied to every channel, and the combined system response. The channel target response is also shown.