Audio Fundamentals
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This document provides an overview of audio fundamentals, including the basics of sound, sound waves, what frequencies the human ear can hear, monitoring sound levels with peak programme meters (PPMs), dynamic range, balance and control, phase reverse, digital audio concepts like sample rate and bit depth, microphones including dynamics and condensers, and polar patterns. The document aims to cover key audio terminology and concepts.
Audio Fundamentals
- 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?