Dynamic Range andDynamic Range

Processors

Relative Sound Level Graph

What is Dynamic Range?

Range of lowest to highest level that can be reproduced by a system

System with a high dynamic range will be quieter than one with a low dynamic range

Dynamic range is measured with the decibel (dB)

Dynamic Range in Digital Audio

Digital Audio at 16 bits has a dynamic range of 96dB This is actually lower due to filter overhead

Digital Audio at 24 bits has a dynamic range of 144 dB

Break it down!

Elements of the previous diagram:1. 0 dB – Unity, also called the permitted maximum level (PML)

2. Dynamic range – difference between permitted loudest and softest signals at the given bit depth

3. Headroom – the amount by which the signal is able to exceed the PML before clipping occurs

4. DSP noise floor – undesirable noise in the system; more on that on the next slide…

Things to notice: as bit depth increases, DR increases, headroom increases, and noise floor decreases.

Signal to Noise Ratio

Ratio between the loudest signal and noise that is inherent in the system (i.e. background noise, hiss, hum, etc.)

Each additional bit of resolution increases the signal-to-noise ratio 6dB!

Example: Audio CDs have about a 90dB signal to noise ratio 16-bit audio has a DR of 96 dB, 6 dB consist of the

noise floor, resulting in a 90 dB signal to noise ratio

Signal to Noise Ratio Graph

Significance to Recordings

Dynamic Range vs. Hearing

We don’t hear the same over the entire frequency range of hearing!

The ear is more sensitive in certain frequency regions than in others

Fletcher-Munson Equal/Constant Loudness

Curves/Contours

Sometimes called “phon” contours

Based on work at Bell labs in 1930’s

People judged when two pure tones of different frequencies were the same loudness

Most sensitive region = 2700-3200Hz

EXAMPLE: a sine wave at 3kHz with a certain intensity will sound LOUDER than one at either 200 or 8000 Hz with the same intensity

Fletcher-Munson Equal/Constant Loudness

Curves/ContoursPhon=SPL indBat1000Hz

Dynamic Range Processing

We can control dynamic range of recordings!

Bit depth tells us the total amount of dynamic range in a recording

We can further controls dynamic range with devices called dynamic range processors

What are dynamic range processors?

Devices that control dynamic range of a signal

4 types Compressor Limiter Expander Noise Gate

Compressor

Like an automatic fader

REDUCES dynamic range

Essentially turns DOWN louder signals, thereby allowing you to increase your amplitude

Makes softer signals seem louder and louder signals seem softer Does not impact softer signals! Only louder signals

Compressed Waveform

Original signal

Compressed signal

Compressor components

Input gain How much input goes into compressor

Threshold User-defined level at which compressor begins to

REDUCE input signal

Output gain How much signal is sent to output

Compressor components (continued)

Ratio Amount of gain reduction Determines amount of reduction of input signal

needed to cause 1 dB increase in output signal Ratio 4:1 produces 1 dB increase in output for every 4

dB increase in input Meaning, if the input is 4 dB over the threshold, the

output will be 1 dB over the threshold Ratio 2:1 produces 1 dB increase in output for every 2

dB increase in input

Compressor Diagram

Compressor components (continued)

Attack Determines how fast or slowly device will turn down

signals that exceed the threshold This takes time. Sometimes can hear “pumping” or

audible changes in dynamic Slower attack = gradual addition of compressor Fast attack = immediate addition; can hear pumping Too slow = can hear compressor engage

Knee Determines slope of the compression Defined as “hard” or “soft”

Knee

A soft knee gradually increases compression ratio. A hard knee will be a more abrupt addition of compression.

Compressor Diagram 2

Peak vs. RMS Compression

Compressors can have “peak” or “RMS” settings for how compression is applied

Peak – responds to instantaneous level of input signal Usually used to compress transient attacks (drums hits) Good for transients, but can yield in abrupt gain reduction

RMS – applies root mean squared averaging function before comparing input to threshold Often yields smoother compression results

Limiter

Compression to the extreme

Used to keep signal peaks from reaching certain level

Most have ratios of 10:1 or 20:1 (or more) Logic allows 30:1 compression within the compression insert

2 functions: Prevent short term peaks from reaching their full amplitude

and minimizes distortion Prevent signal levels from increasing beyond specific point,

which prevents blowing equipment; prevents distortion

Expander

INCREASES dynamic range of a signal

Most expanders decrease the gain of a signal as the level falls below a threshold

Reducing low level signals will increase the signal’s overall dynamic range Why?

Can also be used as noise reducers

Expander

Same components as compressor Input/output gain, threshold, raio, attack

Attack/release settings must be set carefully to best match material Fast release = can get pumping effect Slow release = can cause dynamics to return to

normal state too slowly

Expander diagram

Expander Diagram 2

Noise Gate

Expansion to the extreme

Signal above threshold passes without interference

Signal below threshold closes “gate” and mutes signal

Sidechain input = special input into noise gate Allows external analog source to trigger gate’s

output path