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Digital Audio Basics

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Jim Killgore

on 8 January 2015

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Transcript of Digital Audio Basics

Digital Audio Basics
Digital Audio
PCM (Pulse Coded Modulation) - the method most digital recording devices use
Digital Audio
Analog to Digital Converter (A/D)
Sample Rate
Dictates the highest frequency a system can record
Sample Rate
Let's put a few things together
Bit Resolution and Dynamic Range
CD quality uses 16 binary digits to represent the value of each sample which is known as BIT RESOLUTION
Audio is an analog format and varies smoothly
A digital device is like a camera - it takes pictures of the waveform at specific intervals
Changes the analog waveform into discrete samples
The samples are taken a regular intervals in time
This is known as the Sampling Frequency or Sample Rate
Nyquist Theory
states that the sample rate must be at least double the highest frequency to be recorded
Allows for sample measurement during the positive and negative portion of that frequency's highest waveform
Standard CD sample rate is 44.1Khz - or 44,1000 measurements the waveforms amplitude are taken per second.
So the highest frequency that can be captured is 22,050Hhz
The range of human hearing is 20Hz to 20,000Hz
Why record at higher sample rates?
Bit depth relates to dynamic range
How to calculate dynamic range of a PCM system
# of bits X 6 dB
16bit system X 6 dB = 96dB dynamic range
Bit Depth
Unlike analog, digital is non-continuous so the amplitude scale is "stepped" into integer values.
16 bit system has 65,536 steps
Binary is 1 or 0, so 2 steps
2 to the 16th power
If a sampled amplitude falls between two of those values, it will be rounded to an adjacent integer
Causes a form of distortion called QUANTIZATION ERROR
Bit Depth visuals
How a DAW deals with those numbers
Engine (voice)
Computer resources required to record, play, and process a tracks audio
Resources come from either the host or the DSP hardware of a DAW (Pro Tools HD)
Number of available voices defined by a systems configuration and available hardware
How DAWs deal with those numbers
digital audio needs to be delivered in a linear manner (realtime)
RAM buffer – an application of RAM to regulate data flow to and from the drive
”holding area” for audio to be delivered to and from HDD
RAM Buffer
Pro Tools 11 sets this number automatically. Requires 4GB of RAM
RAM Visual
How DAWs deal with those number
a storage device or transmission channel must have a sustained transfer rate which can keep up with task
Transfer Rate
defined as the speed which data is carried from once device to another and measured in “number of bits per second”
Digital Audio
Use of computers allows for easy manipulation of audio
Low cost, powerful machines and software means anyone can work with audio
Integrated software environment that allows recording, editing, mixing, processing and distribution of music
Define DAW
Digital Audio Workstation
Lots of options of DAWs but we are talking Pro Tools
Features of a DAW?
Multi-track recording – capture multiple channels of audio or MIDI
Waveform editing – perform detailed editing at sample level
Loop construction – making beats
Mastering/CD creation – final processing of audio
Virtual Instruments – software implementations of sound generators - “fake” instruments
More DAW features
Programs that work with a host – usually not a stand alone program
Expand capabilities of host program
Function as signal processors (Eqs, reverbs, delays, dynamics, etc.)
Work in real-time or file based (audiosuite in Pro Tools)
Digital Audio
So how does a sound waves turn into a pretty picture on your screen?
Analog signal
A/D Converter
Full transcript