- May 22, 2017
- Arizona, USA
My AV System
- Preamp, Processor or Receiver
- Marantz AV7705 Pre/Pro
- Main Amp
- Rotel RMB-1066 6 chnl P-amp x 2
- Additional Amp
- Behringer DCX2496 x 2
- Universal / Blu-ray / CD Player
- OPPO BDP-103 Universal Player
- Front Speakers
- DIY SEAS H1456/H1212 Spkr x 5
- DIY JBL 2235H 15" SW x 2
- Video Display Device
- JVC DLA-X790R
- Da-Lite Da-Snap 39105V - 92"
Check Wiki. I think it is just the 1st derivative of the phase slope.
It is negative here as a result of the chosen FDW. The spikes here are just highlighting the strong early room effects that cause strong phase flips - typically nulls.
A larger choice of FDW may make those spikes positive, but also brings in more of the later room influence and the direct sound GD is thus hard to pick out. The point here is to see the group delay of the direct sound rather than the chaos of the later room effect. So the positive or negative spikes are just ignored.