Sound Engineering

Question 1

Explain the following:
- dBfs
- dB SPL

(Include standard measurement for below)

• dBu
• dBm
• dBV

Whats the conversion of (dBfs to dBu)

Answer 1

• dBfs : dB relative to full scale
• dB SPL: dB sound pressure lv (volume changes in environment by ear)
• dBu: relative to voltage (0.775 volts)
• dBm: relative to power (1 mWatt)
• dBV: relative to voltage (1 volt)

0 dBu = -20 dBfs

dB are logarithmic/relative to the source, there is no exact linear measurement

Question 2

What is sample rate and bit depth in relation to sound

Answer 2

sample rate is the “quality” of the sound reproduced

bit-depth determines the amplitude range of the sound produced

Question 3

What is sound v.s audio?

What waves make up sound?

Answer 3

Sound is the “free” live signals you hear in the environment

Audio is the “captured” recorded signals of sound

Sine Waves

Question 4

Sound is measured by what 3 aspects?

What determines the tonal quality of sound?

What determines the pitch of the sound?

Answer 4

Amplitude
Frequency
Time

Timbre = tone (sum of multiple sine waves)
Frequency = pitch

Question 5

What is phase degree and what is the range?

Answer 5

Phase degree is the value at which waves are in/out of phase

0 = perfectly in phase
180 = complete phase sound cancellation

Question 6

What is beating?

How do you calculate the rate of beating?

Answer 6

When waves of 2 different frequencies clash and cause fluctuations in loudness (vibrato)

Take the difference in frequency and that will be the rate/second

Question 7

What is FFT (Fast Fourier Transform)

Answer 7

Mathematical process by which complex waves are broken down into their component sine waves

Pertaining to captured audio spectrum analyzers

Question 8

Describe the purpose of

White Noise

Pink Noise

Answer 8

White - plays every frequency at the same amplitude. (used to test a device’s output)

Pink - plays the fully frequency spectrum at an even volume (used for human audio referencing)

Question 9

Fletcher-Munson Curves

Answer 9

A standardized chart showing the range of sensitivity in human hearing

Concludes that we are more sensitive to the midrange (where human voice lies) so usually there is compensation needed for the low and high range

Question 10

What is the doubling value increase for the following in dB

Amps

Voltage

Acoustic Power

Answer 10

Amps = 3 dB

Voltage = 6 dB

Acoustic Power = 10 dB SPL

Question 11

What is the Haas Effect?

How much quieter is a sound played out of only one speaker vs in stereo at the same time?

Answer 11

Any sound being played from 2 separate sources at around 25ms delay or less will be heard as one sound

Sounds are -3 dB quieter in mono

Question 12

What is the zero crossing line? (ZCL)

Answer 12

In a cyclical sound wave it is the zero crossing point between the positive/negative axis where there is no sound.