Professional Diploma in

Sound Engineering

Lesson 5: Real vs Digital Acoustics

Real vs Digital acoustics

Distinguish between early and late reflections

Lesson 5

Know the difference between reverb and delay

Understand using reverb and delay

Add delay for musical and non-musical effect

Objectives

Acoustics

How sound bounces Echo in the mountains

Reverberation the kitchen

Understand our environment

Propagation and reflection

• In an ideal setup, vibrating sphere = free field

• Sound waves propagate omnidirectionally

• Sound waves lose power over distance

Free fieldImagine hanging in the air

No objects/surfaces for sound reflection

Only hear your own voice in your head

Anechoic chambers

Simulate free field environments

Absorb all sound

Most quiet rooms in the world

(Animations for Physics and Astronomy, 2020)

Wave propagation

Spring model

Air molecules push and pull

Compression and rarefraction

ReflectionSound bounces off surfaces

Tiles and walls vs couches and pillows

Cinema vs parking garage

Standing waves

Sound reflects between two

surfaces

Wavelength = distance between

surfaces

Wave + reflected wave = phase sum

116 Hz = 3M wavelength

• Two walls 3m apart

• 116 Hz tone = 3m wavelength

• 332 Hz = 1.5m wavelength

• Peaks coincide = wave amplify

Standing Waves

(Treci, 2012)

Two waves with the same frequency, wavelength, and amplitude travelling in opposite directions will interfere and produce a standing wave or stationary wave.

Standing waves have higher amplitudes

In your studio

We hear them louder than the original sound wave alone

If there are standing waves in our studios, we will make mixing mistakes

DiffusionStanding wave has constant pressure nodes

The nodes don’t move and create a standing wave

Break the standing wave through diffusion

Diffuse 6 surfaces

Every room has thousands of modes

Diffuse sound to spread energy evenly

Disrupts pressure nodes

Avoid reflections!

In studio we prefer direct sound from

monitors

Reflections mix with direct sound and

changes how we hear the mix

We need to minimise reflections to hear the mix correctly

• Each block mathematically determined

• Design depends on room dimensions

• Every diffuser is unique to the room it is built for

Diffuser panels

Unique diffusersReflected sound and direct sound mix

We hear the mix wrong

Build your own

Address reflections

Diffuse standing waves and other sound

Software to perform calculations

Absorption

Improve sound quality of a room

Reflections have a lot of power

Absorption to reduce power of reflections

Absorption panel = sound airbag• Absorbs some sound

• Reflects sound – with less power

• Acts as an airbag to absorb most of the power

Reverberation

Early reflections Late reflections

• Reflections take less than 100ms

• Many fast reflections

• Reverb: used for sonic enhancement

Early reflections

RT60Reverberation time of a room

Time taken for sound power to drop with 60 dB

Reverberation time• Material, dimensions of surfaces

• Direct sound vs reflected sound

• Compare rooms in your house: clap and listen

Reverb in a DAW

• Digital models are practically endless

• Blend instruments and other sonic elements

• Adjustable parameters: Decay, feedback, wet/dry mix, HP/LP filter

Reverb: decaySound reflects many times

Thousands of reflections in a sound

How quickly will reflections stop?

That’s the decay setting

Types of reverb • Indoor vs outdoor ambience• Direct vs reflected signal

Wet/dry mix

Direct vs reflected sound ratio

Wet is more reflected sound

Dry is more direct signal

What is delay?

Late reflections After 100 msSounds like an

echo

Reflections

Early reflections indicate space

Late reflections sound like a echo

In a DAWCopy of original signal played a little later

Contributes unique features to music

Time delay• Two main delay settings: time and beats• Match tempo to blend instruments and vocals• Set in ms to highlight an element

More controls Low pass filter = LP

Ping pong delays

High pass filter = HP

Stereo highlightsDelay out of sync with tempo

Time in ms

Blending delays

Related to tempo

16th notes faster delays and more stutter effect

¼ note – whole note delays for smoothing out

Blending with filters

LP filter = warmer delays

HP filter = brighter delays

Vocals = go try it for yourself!

Acoustics

Conclusion

Earl reflections = reverb

Late reflections = delay

Early reflections• Gives sense of space• Enhance acoustics with reverb• Podcast – no or very little reverb• Pop Vocals – probably more• Add width to stereo field

Late reflections

Sound fullness Smoothen melodies

Reverb vs Delay

Use with caution Small amountsListen with

your ears, not your eyes!

Completed lessons

1

6 7 8

See you soon for

L e s s o n 6

2 3 4

5