Last Friday 18 we celebrated our main event of the year, the 4th edition of our beloved "Audio Expertos", held both in person and by streaming.
This year we proposed a different format for the event, we prepared various workshops concerning to topics related to our three departments (being those acoustics, audio and immersive audio), in a way that they explicitly relate to each other, as it follows:
-First, we prepared a tetrahedral first order Ambisonics microphone array, consisting of four SM81 cardioid condenser microphones disposed as stated in the Frank & Zotter's book "A Practical 3D Audio Theory for Recording, Studio Production, Sound Reinforcement, and Virtual Reality". The four microphones were going through an UMC404HD from Behringer. Not only the array itself, but also the theory involved and the routing, plugins and tools that are relevant for a workflow of this type, were explained by Carla Gatica and Diego Flores. During the talk, attendants were encouraged to listen to a binaural mix of the array. The plugin chain was the following: Ambeo A-B Converter, Blue Ripple Sound visualizers, IEM binaural decoder.
-After the 3D audio talk, the Audio department took the word to explain how to time-align a sound reinforcement system at one point in the room. The purpose was to fine tune the spot where the Ambisonics array was built, and thus to have the best time coherence of signals produced by a 3.1 speaker system arriving at that point, that was used to play a piece of acousmatic music composed for that day. Federico López prepared a set of captures of measurements to show us how to compare the time arrivals of pink noise coming from the different speakers of the system to a measurement microphone that was set very close to the Ambisonics array. Several delays were applied to some signals, in order to time-match with each other. To explain what was mentioned earlier, Open Sound Meter was used for all the measurement and comparison between the calibrated and not calibrated system.
-Finally, the acoustics part took place. Leandro Rodriguez gave us an introduction to impulse response measurements. Mono and binaural (with the binaural decoding from the Ambisonics array) impulse responses were taken at the critical distance of the room, searching for measuring a point in space where the energy stands integrated. For the measurement, the source was a speaker developing 90dB SPL of pink noise bursts at the point where the microphone was placed. The software "Acoustic tools" helped Leandro to explain some acoustic parameters such as Reverberation Time and C50. C50 showed different comparing mono and binaural impulse responses, being the binaural IR more related to human listening experience. In terms of frequency response, the mono IR resulted in more precision for modal response. The binaural IR turned out to be more accurate for high frequency phenomena.
After the talks related to the three departments, the acousmatic composition was played on a 3.1 system and recorded with the Ambisonics array. Virtual attendants listened to the music live, but decoded to binaural format, while in person attendants listened to the output of the speaker system.
