Meeting Topic: Gain Structure Design for Digital Audio Recording (in English)
Speaker Name: Salvador Tercero, Full Member
Other business or activities at the meeting: As part of our "Primer Audioencuentro Estudiantil de Verano 2011", our next meeting will be held on Thursday, July 21st for a third conference entitled "Sound Architecture" where Salvador Tercero and Humberto Terán will share the techniques they have used to attain certain sounds throughout their careers.
Meeting Location: Estudio "A", Sala de Audio; Heriberto Frías 217 Col. Narvarte, México City, Mexico
Last Thursday, July 14th, the second meeting of the "Primer Audioencuentro Estudiantil de Verano 2011" organized by the AES Sala de Audio Student Section took place. In the conference entitled "Gain Structure Design for Digital Audio Recording", Salvador Tercero gave a fun and inspiring lecture in which he talked about basic concepts we need to understand in order to make a good recording.
He talked about how, in order to understand the magnitude of a sensation, human beings need to compare it to another one. That's why we use the decibel, a unit that simplifies the relationship between two different quantities, to describe the intensity of a sound or audio signal.
He then spoke about microphones as transducers that convert the characteristics of sound (intensity, musical pitch and timbre) and translate them into an audio signal with amplitude, frequency and waveform. He talked about the way different types of microphones work and their frequency response and polar pattern, and how they are the first step in a gain structure. We should choose the right microphone and place it in the correct position in order to capture a signal with the harmonic content and level that we want.
He went on to talk about sensitivity. He explained a microphone's sensitivity is it's transduction factor; that is, the level of the electric signal that the microphone will output given a certain level of sound pressure. A gain structure should be designed so that the signal reaches 0 dBv with the least possible pre-amplification. "I close my pre-amp and open my fader" to get the cleanest possible signal.
Salvador said, "digital audio is analogue to analog audio". This means that, in digital audio, we also have a department dedicated to transducing signal intensity (bit depth) and one dedicated to transducing harmonic content (sample rate).
He explained how dynamic range is, as mentioned earlier, the relationship between a maximum and a minimum intensity. He gave graphic examples of how intensity relates between the world of sound (sound pressure), the world of analog audio (voltage) and the world of digital audio (bit depth). He said the idea is to work with audio signals that are, taking the sound source, the microphone's sensitivity and the pre-amplification level into account, around 0 dBv so that when they pass through the analog/digital converter, they get to be around —18 dBFS.
The lecture finished with Salvador inviting the 60+ assistants to our next meeting (mentioned above in the "Other business and activities at the meeting" section) and asking them to join AES, the most important audio society in the world.
Written By: Víctor Stern