Week 2: Acoustic Theory; Recording Theory

This page is for lecture notes from week 2 of MUSM 342 - Recording Studio Techniques with Dr. Merlyn Van Regenmorter.

Lecture Notes
Sound, how do we capture it?

Sound
Sound happens due to periodic variation of atmospheric pressure.Atmospheric
 * Pressure – The amount of molecules in a given space.
 * Compression – When the atmospheric pressure increases above normal.
 * Rarefaction – When the atmospheric pressure is lower then normal.
 * Sound Pressure Wave – Periods of Compression and Rarefaction

1.) Frequency (Perceived as pitch)
Frequency is the amount of cycles per second (cps) we also refer to this as Hertz (Hz)

Frequency Spectrum – Range of all potential frequencies
 * >20Hz = Infrasonic (Subsonic Range)
 * 20Hz – 20kHz = Audio Spectrum
 * <20Hz = Ultrasonic

2.) Amplitude (Perceived as Volume)
Measurement of signal intensity and/or volume (perceived signal intensity). It's measured in decibels (dB).

Amplitude is the amount of displacement in atmospheric pressure. You can hear down to 2/10,000 of 1 Microbar (1 Million Bars)(1 bar = normal atmospheric pressure)
 * Threshold of hearing: 0 dB = 2/10,000 of 1 Microbar
 * Whisper is around 30 dB
 * Normal conversation 60 dB
 * Baseline for editing 85 bB
 * Threshold of feeling: 115 to 118 dB
 * Threshold of pain: 140 dB

3.) Timbre
The quality of the sound (The fundamental and it's overtones) This is what allows you to distinguish between different instruments.

Sine Wave – Represents only one frequency – Just the fundamental free of all overtones

Anatomy of a Sound wave
Sound waves are normally going to be measured in seconds
 * Peaks – Area that's currently experiencing Compression
 * Troughs – Area that's currently experiencing Rarefaction
 * Cycle – A Sequence from one peak through one trough.

60 Cycle hum, this is usually a grounding issue. This

Standard of tuning in the western world = 440Hz = A

The human ear can theoretically hear from 20Hz to 20,000Hz out of the womb.

Harmonic Series

 * Fundamental – Primary Pitch
 * Octave above – Primary frequency doubled
 * Overtones - Notes over the fundamental

Complex Wave forms – Illustrates all the frequencies in the fundamental and wave form

When two wave forms combine in a way that brings the first wave form to have increased signal this is constructive interference

When two wave forms combine in a way that brings the first form signal down, this is destructive interference.