Meeting Topic: Recording BRIR´s from an octophonic setup
Moderator Name: Leandro E. Rodríguez
Speaker Name: Leandro E. Rodríguez, Federico López
Other business or activities at the meeting: Planning the individual convolution tasks with the previously obtained semianechoic stimulus
Meeting Location: Buenos Aires
We reunited in studio 2 in order to make BRIR´s (Binaural Room Impulse Responses) in an octophonic setup, in different ways. After calibrating the system with minimum delay adjustements (obtaining +/- 3 dB in the spectrum in the spot at 90 dB SPL) we obtained discrete mono IR´s of the eight monitors (the Ambisonics group put pressure to do this task...). After, we recorded BRIR´s of our own anatomies, with a pair of our best SM81´s, and also "a invisible guy" and our own dummy head (Liza). All these signals, transfer function included, were carefully calibrated case by case, and in the meantime we make several trials of binaural front-back confusion perception, our main task in the Binaural group (we are going to make a formal experiment with the HRTF information of this BRIR´s with a convolution with the previously obtained stimulus in the ECOS semianechoic chamber). Launching the same pink noise burst in three trials (front quad, back quad, full octo) and knowing the acoustical characteristics of the studio and also counting with our own previous quadraphonic experience in-place we reached some informal conclusions:
• On individual HRTF´s with acoustic convergence, the confusion is not front-back: is front. Back signals were perceived correctly 100%.
• The suggestion factor is great. In some trials we intentionally send mono signals to the headphones and the reported directions were "front", "back", "all", "I don´t but it´s outside my head", etc.
• On non-individual HRTF´s -including our dummy and "the invisible guy" (A/K/A no head and torso, only the mics) the directivity of the signal is confusing (control experiment).
The eight EVE Audio SC-205 studio monitors were generously supplied by Planeta Analógico. Thanks Fernando Richard!
With all of these captures we´re going to make final stimulus for an experiment with lure sources and acoustic convergence in October! And a lot of more things for 2020 (HRTF´s comparision and database, Ambisonics deployment, etc.).
Written By: Leandro E. Rodríguez