Visualizing Sounds

Introduction

My name is José M. Pérez. I am from Barquisimeto, Venezuela. This week we will be learning about Sound Visualization, according to lesson for week 1 of Introduction To Music Production at Coursera.org.

A little theory first...

¿What's sound? Sound is a vibration that propagates as a mechanical wave of pressure and displacement, through some medium (such as air or water). Although sometimes sound refers to only those vibrations with frequencies that are within the range of hearing. 

For visualizing sound, we have to know some other terms related, such as:

Amplitude

Amplitude is related to the extent of the wave, how wide it's moving, or how much the air compresses and rarefies as that wave form moves or propagates through the air. Visually, looks like the height of a waveform above or below its zero baseline. Amplitude is also referred to as signal volume, and looks like this: 

Frequency

Frequency refers to the rate or speed at which an audio source generates complete cycles in one second. This property determines the pitch of the sound. It is only useful or meaningful for musical sounds, where there is a strongly regular waveform.

Pitch

Pitch is closely related to frequency, but the two are not equivalent. Pitch is an auditory sensation in which a listener assigns musical tones to relative positions on a musical scale based primarily on the frequency of vibration. In other words, pitch is the frequency of a note determining how high or low it sounds.

Tools for visualizing sounds

Oscilloscope

Is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time. Non-electrical signals such as sound or vibration can be converted to voltages and displayed.

The oscilloscope measures the amplitude of the wave on the y (vertical) axis and time on the x (horizontal) axis. In the next example, Y axis is simply a linear scale with 0 as no signal and 1 or -1 as a fully saturated signal. You can see that the amplitude of the wave is decreasing over time, and that the frequency is growing higher because the distance between waves is shorter.

Spectrum Analyzer

A spectrum analyzer measures the amplitude of an input signal (y axis) versus frequency within the full frequency range of the instrument (x axis). The primary use is to measure the power of the spectrum of known and unknown signals. This provides a snapshot into the energy distribution by frequency. Since it is a snapshot, it doesn't contain information on how those energy distributions change over time. Common applications include measurements of distortion, and to measure the harmonics within a signal.

Sonogram

Is an instrument that separates an incoming wave into a visual representation of the spectrum of frequencies in a sound or other signal as they vary with time or some other variable. The sonogram represents time on the x axis, frequency on the y axis, and amplitude mapped by color change. It gives the clearest picture of how our ears actually hear over time. In the next sonogram we can see that the amplitude of the wave is decreasing over time while the frequency is increasing. It provides a good sense of frequency increasing as decibel level decreases.

Reflections

Thanks very much for reading. The material wasn’t new to me but I needed to write a script to reafirm and clarify the terms, and when I was doing this post I learned some things that I was missing. I hope this info may be useful like it was for me, and I would love to know if I got everything right. If there's anything I missed or could have explained better, please comment and I would be happy to modify or correct what's necessary.