FIR Designer M : Channels – FIR Auto Phase
This view is the fourth 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 phase 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 degrees, is applied. When edges of two bands come to within the octave smoothing distance, from either band, a cross-fade is applied between the two bands.
The red line in the upper plot shows the loudspeaker phase response – after filtering from preceding tabs – subtracted from the channel target phase response.
The aim is to use filter prototypes to match the green line – the filtering for this tab – to the red line. When closely matched, the loudspeaker response – after filtering – will be closer to the channel target.
| 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. |
Auto Phase Response
This plot shows the magnitude and phase for all preceding tabs up to, and including, the Auto Phase, applied to every channel, and the combined system response. The channel target response is also shown.