Basics of sound theory for studio managers and other operational staff in broadcast audio and radio.

1. Audio Fundamentals
James West, March 2021

2. IWS 91/2

3. What are we talking about today?
• Basics of sound
• Vocabulary
• How it works
• Waveforms
• what can we hear?
• Monitoring sound – the PPM
• Dynamic range
• Balance and control
• Phase reverse
• Digital audio
• Sample rate
• Bit depth
• Microphones
• Dynamics and condensers
• Polar patterns

4. Basics of sound
• What’s our vocabulary for describing sound?
• How does it work?

5. Sound waves in the air

6. Sound waves in the air

7. Basics of sound
Anatomy of a waveform:
• Amplitude
• Wavelength
How do these relate to pitch and
volume of the sound?

8. Basics of sound
• What can we hear?
• Frequencies from…

9. Basics of sound
• What can we hear?
• Frequencies from 20Hz to 20kHz

10. Basics of sound
• What can we hear?
• Frequencies from 20Hz to 20kHz
• Volumes from…

11. Basics of sound
• What can we hear?
• Frequencies from 20Hz to 20kHz
• Volumes from the threshold of hearing at 5dBA to jet aircraft at
120dBA.

12. Effect of noise on the listener Level in dBA Example
PAIN 140 Jet engine - near
Deafening 120 Jet aircraft at 150m
Very loud 100
95
90
Orchestra or loud car horn at 5m
Small jet aircraft at 200m
Busy street
Loud 80
70
60
Orchestra at 5m
Radio at full volume from 3m
Normal conversation from 1m
Moderate 50
40
Inside quiet car
Inside quiet house
Faint 30
20
10
Whisper from 1m
Inside quiet church
Sound proofed room
Very faint 5 Threshold of hearing

16. Peak Programme Meter
• White markings on a black
background
• Rapid rise to peaks followed by
slow decay
• Scale from 1 to 7
• 4 dB between divisions
• 0dBU reference level for line up
is PPM 4
• Peak level is PPM 6 (8dBU above
reference level)

17. Stereo PPMs
• Red and green needles are left and right audio measured from the
desk
• White needle is the Middle. It’s the sum of left and right with 6dBU
subtracted
• M = (L + R) - 6dBU
• This is what listeners in mono are hearing
• Yellow needle is the Side signal.
• It’s the difference between left and right
• S = (L - R) - 6dBU
• It tells us how “stereoy” the sound is

18. What do PPMs tell us?
• Shows us the peak audio level
• No indication of subjective loudness or level relative to other sounds
• Use your ears to balance the programme and the PPM to help and
guide you – this is one of the key skills of SMs!

19. Dynamic range
• The difference between the loudest and quietest parts of the sound
• What do we do on the desk to reduce the dynamic range?
• How does that work?
• Where else does dynamic processing happen to our output?
• The processors for the different platforms work best if there’s some
dynamic range left in the audio fed to them. Don’t squash it all
against 6.

20. Balance and control
Balance
• Making a nice sounding
programme
• This is the arty and creative side
of our job
Control
• Keeping it within the parameters
set for your network
• Don’t peak over 6!
• This is the technical side of our
job

21. Phase reverse
You get two clues on pre-fade
• It’ll sound quiet, because the pf
speaker is mono
• The PPMs indicate it clearly
• Why is this is a big problem for
mono listeners?

22. Digital audio

23. Sample rate and bit depth

24. Sampling rate…
• …is how often you measure – or sample – the waveform.
• How do we decide what sampling rate to use?
• Nyquist’s theory tells us you should sample at a rate double the
highest audio frequency you want to capture, plus a little bit.
• If we ignore this and set the sampling rate too low, aliasing can occur
• So, when we’re recording audio for humans, how do we work out a
good sampling rate?

25. Bit depth…
…describes how accurate each sample will be
• 8 bit samples allow values between 0 and 255 - 11010110
• 16 bit lets us measure between 0 and 65,535 - 0111001011010110
• More bit depth gives us more dynamic range
• Higher bit depths also reduces the effect of quantising errors

26. Microphones
Dynamic mics
• Moving coil – omnidirectional or
cardioid polar pattern
• Ribbon – figure of eight polar
pattern
• Tend to be more robust than
capacitor mics and can be hand
held
• Need a lot of gain added at the
mic pre-amp

27. Microphones
Capacitor/condenser mics
• Diaphragm with an electrical
charge
• Requires phantom power (+48v)
• Are more susceptible to handling
noise and perform better on a
stand
• Much loved by presenters for
their proximity effect, aka bass
tip-up

28. Polar patterns

29. How did we do?
• Basics of sound
• Vocabulary
• How it works
• Waveforms
• What can we hear?
• Monitoring sound – the PPM
• Dynamic range
• Balance and control
• Phase reverse
• Digital audio
• Sample rate
• Bit depth
• Microphones
• Dynamics and condensers
• Polar patterns
• Got any questions?