AUD 170 - Project 1 - Calvin and Nathan

Sound Theory Project 1

AUD170.1 Fundamentals of Sound - Calvin and Nathan 28th Feb 2021

Flash Cards “Learning a new language”

Frequency (hertz)

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Frequency (hertz)

• Frequency is measured as the number of wave cycles that occur in one second, the unit for measurement of this being hertz (hz).

• Hertz is used commonly to measure wave frequencies, the human ear being able to pick up sound waves between 20 and 20,000 hz (20 kilohertz).

• Kilohertz is a measurement of hertz above 1000, where 1 kHz = 1000 hertz.

Phase

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Phase • Phase is de ined as how far along the sine wave signal is in the current cycle.

• In practical terms, an audio track can be de ined as ‘in phase’ when the left and right channels’ sine waves are moving in the same way, at the same time.

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• It can be de ined as ‘out of phase’ when the sine waves are moving in opposite ways at the same time, and if they’re perfectly opposite, this will usually result in complete silence.

Phasing

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Phasing • Phasing is a time-based e ect that can be used in the form of a physical e ect pedal, or as a plug-in on a DAW. • This is a technique in which the phasing device – called the Phaser – takes the original sound, and makes a copy of this sound, moves it slightly o -tempo, and samples it back against the original.

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• This sound is created using Phase Cancellation, which happens when a sine wave is ‘out of phase’

Compression & Rarefaction

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Compression & Rarefaction • Compression is a region within a sound wave where the particles are closest together.

• When an object vibrates, it irst pushes the air particles surrounding it, creating compression in the sound waves.

• It then pulls the air particles apart, creating rarefaction.

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• Rarefaction is a region within the sound wave where the particles are the furthest apart.

Sample Rates

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Sample Rates • Sample rate de ines the number of samples per second taken from a continuous signal to create a digital signal.

• As a rule, the sample rate must be double the highest frequency of the audio track being sampled.

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• However, the Nyquist Principle states that perfect reconstruction of a signal is possible when the sampling frequency is greater than twice the maximum frequency of the signal being sampled.

Fundamental Frequency

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Fundamental Frequency • The fundamental frequency is the lowest frequency produced by a waveform, as distinct from the harmonics of a higher frequency.

• For example, the note A on a piano has a fundamental frequency of 440hz. This means that each interval between harmonics will be 440hz, and every-time the harmonic is double the previous A, this will be an octave above.

• E.g. 440hz is A1, 880hz is A2 and 1760hz is A3, etc.

Harmonics

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Harmonics • Harmonics are all whole number multiples of the fundamental frequency produced by a waveform.

• For example, the note A on piano has a fundamental frequency (or alternatively, irst harmonic) of 440hz, therefore the second harmonic, A2, will be 880hz, and the third, E6, will be 1320hz.

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• Harmonics create sounds well above the range of human hearing, and before digitalisation of equipment there was ampli iers that could produce sounds up to 60kHz!

Mono & Stereo Mixing

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Mono & Stereo Mixing • Mono and stereo mixing are di erent techniques used to produce, mix and master music.

• Mono mixing refers to the act of mixing where all tracks will output the same audio from both sides of headphones or speakers.

• Stereo mixing will often pan the sound, as di erent audio signals are driven through left and right speakers.

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• Because of this di erence in the audio signals, a mix will usually sound far di erent when changing from mono to stereo, or vice versa.

Frequency Response Chart

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Frequency Response Chart • A frequency response chart is a tool used by audio engineers in order to understand how certain responsive certain equipment is, speci ically microphones.

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• It is generated by testing the microphone in an anechoic chamber, a specially constructed room for audio testing, in which the room is acoustically dead with no form of sound re lection.

Dynamic Range

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Dynamic Range • The dynamic range is the ratio between the highest and the lowest frequencies of an audio track, instrument or piece of music.

• Typically, in modern day recordings, the dynamic range of a piece of music is far less than before digitalisation of music production, as compression is far more advanced nowadays, which prevents tracks from clipping in some parts, and then being far too quiet in other parts.

Clipping

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Clipping • Clipping refers to a form of waveform distortion, which occurs when an ampli ier or digital audio track is pushed past its limits, and attempts to deliver an output voltage or current beyond its maximum capabilities.

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• As aforementioned, a compressor, whether physical or digital, can be used to minimise the dynamic range in a track, therefore eliminating parts where the audio would be clipping past its maximum range.

Sine Waves & Square Waves

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Sine Waves & Square Waves • A sine wave describes an audio waveform which is a ected by two things; pitch and volume. The higher the pitch, the faster the wave, and vice versa.

• A sine wave does not have ixed points, the highest and lowest points being de ined by the pressure in the air created by vibrations.

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• A square wave has two ixed minimum and maximum points, and the amplitude alternates at a steady frequency between these values, with the same duration at each.

End Questions “Learning a new language”

No: 1 What does it mean if a speaker is or audio track ‘out of phase’.

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It means that the sine waves in the left and right channels are playing the same thing simultaneously.

No: 2

How many hertz equals one kilohertz?

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1000

No: 3 Which refers to the region in which sound particles are furthest apart, compression or rarefaction?

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Rarefaction.

No: 4 Does a sine wave have a ixed minimum and maximum point?

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No, a square wave has a ixed minimum and maximum point

No: 3 How is equipment tested to create a frequency response chart?

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Equipment is test in an anechoic chamber to create a frequency response chart.