Dynamic Range and Dynamic Range Processors. Relative Sound Level Graph.
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Transcript of Dynamic Range and Dynamic Range Processors. Relative Sound Level Graph.
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