Audio Engineering 101

A Beginner's Guide to Music Production

Tim Dittmar

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781317210153
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Acoustical Engineering
• Index: Technology & Engineering

Practical, concise, and approachable, Audio Engineering 101, Second Edition covers everything aspiring audio engineers need to know to make it in the recording industry, from the characteristics of sound to microphones, analog versus digital recording, EQ/compression, mixing, mastering, and career skills. Filled with hand-ons, step-by-step technique breakdowns and all-new interviews with active professionals, this updated edition includes instruction in using digital consoles, iPads for mixing, audio apps, plug-ins, home studios, and audio for podcasts. An extensive companion website features fifteen new video tutorials, audio clips, equipment lists, quizzes, and student exercises.

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CHAPTER 1

What Is Sound? Seven Important Characteristics

In This Chapter:

What Is Sound?

Seven Characteristics of Sound

Amplitude

Frequency

Phase

Velocity

Wavelength

Harmonics

Envelope

Other Periodic Waveform Types

Noise

Analog and Digital Audio

What Is Analog?

What Is Digital?

Digital Audio Terms

Lossy vs. Lossless

Learning the craft of audio engineering is like learning a foreign language. A new language may be intimidating and difficult at first, but, with time and dedication, a vocabulary is built. Soon words turn into phrases and phrases turn into full sentences. This chapter will cover details of a sound wave and explore some of the language of audio. You will be fluent in no time!

WHAT IS SOUND?

Sound is a vibration or a series of vibrations that move through the air. Anything that creates the vibrations, or waves, is referred to as the source. The source can be a string, a bell, a voice, or anything that generates a vibration within our hearing range.

Imagine dropping a stone into water. The stone (source) will create a series of ripples in the water. The ripples (waves) are created by areas of dense molecules that are being pushed together, while areas with fewer expanding molecules create the flatter sections. Sound travels in a similar way to this, by compression and rarefaction. Compression is the area where dense molecules are pushed together and rarefaction is the area where fewer molecules are pulled apart, or expanded, in the wave. The compression area is higher in pressure and the rarefaction area is lower in pressure.

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This chapter deals with the seven characteristics of a sound wave: amplitude, frequency, phase, velocity, wavelength, harmonics, and envelope. You will also be introduced to the various types of waveforms, analog and digital audio, and lossy/lossless formats.

Although a typical sound is more complex than a simple sine wave, the sine wave is often used to illustrate a sound wave and its seven characteristics.

FIGURE 1.1

SEVEN CHARACTERISTICS OF SOUND

You may already know about two characteristics of sound: amplitude and frequency. If you have ever adjusted the tone on your amp or stereo, then you have turned the “amplitude” of a “frequency” or range of frequencies up or down. It is necessary to understand these two important sound wave characteristics, as they are essential building blocks in audio engineering. Two other characteristics of sound help humans identify one sound from another: harmonics and envelope. The remaining three characteristics of sound are velocity, wavelength, and phase. These characteristics identify how fast a sound wave travels, the physical length of a completed cycle, and the phase of the sound wave.

Amplitude

Amplitude is associated with the height of a sound wave and is related to volume.

When a stereo, amp, or television’s volume is turned up or down, the amplitude of the sound being projected is increased or decreased. Loud sounds have higher amplitudes while quiet sounds have lower amplitudes. The greater the amplitude of a sound the greater the sound pressure level (SPL).

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FIGURE 1.2

Amplitude is measured in decibels (dB). Most people can recognize about a 3 dB change in amplitude. A trained ear can recognize even smaller amplitude changes. An increase in amplitude is usually expressed as a “boost” and a decrease in amplitude is often expressed as a “cut.” The word “volume” is often substituted for amplitude. An audio engineer may say, “boost that 3 dB” or “cut that 3 dB.” When amplitude is written out, it is expressed with a positive sign such as +3 dB or a negative sign such as −3 dB.

Here are some common activities and their corresponding decibel levels:

0 dB – near silence

40–50 dB – room ambience

50–60 dB – whisper

60–75 dB – typical conversation

80–85 dB – a blender, optimum level to monitor sound according to the Fletcher–Munson curve

90 dB – factory noise; regular exposure can cause hearing damage

100 dB – baby crying

110 dB – leaf blower, car horn

120 dB – threshold of pain; can cause hearing damage

140 dB – snare drum played hard from about one foot

150–160 dB – jet engine

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As you can see, in our daily lives, we are typically exposed to amplitude levels between about 50 dB and 110 dB. Most people listen to music between 70 dB (on the quiet side) and 100 dB (on the loud side). To learn even more about dBs check out Appendix A.

Frequency

The amount of cycles per second (cps) created by a sound wave is commonly referred to as the frequency. If you are a musician, you may have tuned your instrument to A/440. Here, “440” is the frequency of a sound wave. It is related to pitch. Unlike amplitude, which is measured in decibels, frequency is measured in hertz (Hz), named after the German physicist, Heinrich Hertz. The average human hearing range is from 20 to 20,000 Hz. Typically, once 1000 cycles per second is reached, the frequency is referred in kilohertz (kHz), i.e., 1000 Hz = 1 kHz, 2000 Hz = 2 kHz, and 3000 Hz = 3 kHz. Frequency is related to the pitch of a sound. Figure 1.4 is a handy chart to help identify the frequency ranges of various instruments and how the keys of a piano relate to frequency. The first note on a piano is A, which is 27.5 Hz. Have you ever turned up the bass or treble on your car stereo? If so, you are boosting or cutting the amplitude of a frequency or range of frequencies. This is known as equalization (EQ), a vital aspect of audio production.

FIGURE 1.3

Each frequency range has distinct characteristics, and some common terms can help you to identify them. I will go into further detail throughout the book, but let’s start here:

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FIGURE 1.4

Frequency is often divided into three ranges:

AUDIO CLIP 1.1

https://youtu.be/J1V_Z9gfGyQ

Low or bass frequencies are generally between 20 and 200 Hz. These frequencies are omnidirectional, provide power, make things sound bigger, and can be destructive if too much is present in a mix. Note that frequencies under 30 Hz produce more of a “feeling” than a sense of sound.

Mid, or midrange, frequencies are generally between 200 Hz and 5 kHz. This is the range within which we hear the best. These frequencies are more directional than bass frequencies and can make a sound appear “in your face,” or add attack and edge. Less midrange can sound mellow, dark, or distant. Too much exposure can cause ear fatigue.

High or treble frequencies are generally between 5 and 20 kHz and are extremely directional. Boosting in this range makes sounds airy, bright, shiny, or thinner. This range contains the weakest energy of all the frequency ranges. High frequencies can add presence to a sound without the added ear fatigue. A lack of high frequencies will result in a darker, more distant, and possibly muddy mix or sound.

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Midrange is the most heavily represented frequency range in music. It is often broken down into three additional areas:

Low-mids, from around 200 to 700 Hz: darker, hollow tones

Mid-mids, from 700 to 2 kHz: more aggressive “live” tones

High-mids or upper-mids, from 2 to 5 kHz: brighter, present tones

This chart in Figure 1.5 may come in handy when you are learning how...