Audio Engineer's Reference Book

Michael Talbot-Smith, Michael Talbot-Smith

• Publisher: Routledge
• Year: 2013
• ISBN:
  9781136119736
• Edition: 2
• Topic: Technologie et ingénierie
• Subtopic: Ingénierie de l'acoustique

An authoritative reference on all aspects of audio engineering and technology including basic mathematics and formulae, acoustics and psychoacoustics, microphones, loudspeakers and studio installations. Compiled by an international team of experts, the second edition was updated to keep abreast of fast-moving areas such as digital audio and transmission technology. Much of the material has been revised, updated and expanded to cover the very latest techniques. This is a new paperback version.

1 Basic Principles

DOI: 10.4324/9780080499581-1

• John Ratcliff
  • Proprietor, The Television Training Company
  • 1.1 Mathematics, formulae and equations
  • 1.2 Units used in audio engineering
• Michael Talbot-Smith
  • Consultant
  • 1.3 The physics of sound waves
• J. Patrick Wilson
  • Lecturer in Electronics, Keele University
  • 1.4 The hearing process
• Louis D. Fielder
  • Principal Staff Engineer, R&D and Business Development, Dolby Laboratories Inc
  • 1.5 Perceptual audio coding
• Glynne Parry
  • Senior Calibration Engineer, CEL Instruments Ltd
• Richard Tyler
  • Chief Engineer, CEL Instruments Ltd
  • 1.6 Noise measurement
• Michael Gayford
  • Former Consultant (Deceased)
  • 1.7 Electromechanical analogies
• Roger Derry
  • Audio and Broadcast Consultant
  • 1.8 Introduction to digital audio

1.1 Mathematics, formulae and equations

1.1.1 SI units

The four fundamental SI units are length, mass, time and electric current.

Length (L) The unit of length is the metre (m). One metre is 1 650 763.73 wavelengths in a vacuum of the radiation corresponding to the transition between the levels 2p₁₀ and 5d₅ of krypton-86.

Mass (M) The unit of mass is the kilogram (kg). One kilogram is the mass of the international prototype held by the Bureau International des Poids et Mesures, Paris.

Time (T) The unit of time is the second (s). One second is the duration of 91 926 131 770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of caesium-133.

Electric current (I) The unit of electric current is the ampere (A). One ampere is the current that, flowing in two infinitely long conductors of negligible cross-section spaced apart by one metre in a vacuum, will produce a force of 2 × 10⁻⁷ newtons per metre (N/m) between them.

1.1.2 Derived SI units

Velocity (V) Velocity is the distance/time in metres/second (m/s).

Acceleration (a) Acceleration is the rate of change of velocity. It is given in metres per second (m/s²).

Force (F) The unit of force is the newton (N). One newton will accelerate a mass of 1 kg by 1 m/s².

Work or energy (W) The unit of work is the joule (J). One joule of work is done when one newton of force moves through one metre in the direction of the force.

Power (P) The unit of power is the watt (W). Power is the rate at which work is done: one joule of energy expended in one second requires one watt of power.

Charge (Q) The unit of charge is the coulomb (C). One coulomb is the quantity of electricity passing through a conductor when one ampere flows for one second.

Potential Difference (V) The unit of potential difference is the volt (V). One volt of potential difference exists between two points if one joule of work is done in transferring one coulomb of charge from one point to the other.

Resistance (R) The unit of resistance is the ohm (Ω). One ohm is that resistance in which a current of one amp generates energy at the rate of one joule per second.

Capacitance (C) The unit of capacitance is the farad (F). A capacitor of one farad will raise the potential between its plates by one volt with the addition of one coulomb of charge (Q = CV).

Magnetic flux (Φ) The unit of magnetic flux is the weber (Wb). When a conductor experiences flux changing at one weber per second a potential difference of one volt is produced across the ends of the conductor.

Flux density (B) The unit of flux density is the tesla (Wb/m²). The flux per square metre at right angles to the field is the flux density. Frequently quoted as webers per square metre: B = φ/a (Wb/m²).

Inductance (L) The unit of inductance is the henry (H). A closed circuit has an inductance of one henry when a potential difference of one volt is produced by a rate of change of current of one ampere per second.

Pressure (P) Unit of pressure is the pascal (Pa): one pascal is one newton per square metre (N/m²).

Frequency (f) The unit of frequency is the hertz (Hz). Frequency is the inverse of time (1/s). It is defined as the number of waves passing a fixed point in one second.

Wavelength (λ) Wavelength is the distance between successive points (e.g. crests) on successive waves (see Figure 1.1). Wavelength, velocity and frequency are related by the formula v = fλ.

Figure 1.1 Wavelength is the distance between corresponding points on successive waves, e.g. crests or troughs.

Angle (Θ) Defined as the radian (rad). Two radii of a circle at an angle of one radian will cut an arc equal to the radius of the circle at the circumference. 27π radian = 360°. 1 radian = 57.3°.

Permeability (μ) The permeability of space (μ₀) is the ratio of the flux density (B) to the magnetizing force (H) i...