Technology

ICTOption: Audio

Digital Audio

•Sound is represented as Analogue Waves

•Sound must be converted to a Digital Form to

be processed by a computer

Sampling rate

Analogue signal

TimeAm

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Digital Audio

•Sound wave is measured at regular intervals

•Process is called Sampling

•Number of samples /second is the Sampling

Rate

Sampling rate

Analogue signal

TimeAm

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Recording Digital Audio

Audio can be recorded into a computer using:

•External microphone

•External player - tape or record player

•Internal player - CD or DVD Rom drive

Microphone (Pink)

Speakers(Green)

External Player (Blue)

External ports:

Recording Digital Audio

When the recorded sound reaches the

computer’s Sound Card, an ADC (analogue

to digital convertor) converts the sound to

digital values. The number of values taken is

set by the sampling rate.

Recording Digital Audio

Factors affecting the recording quality:

•Sampling rate - samples taken per second (Hz).

Audio CD is recorded at 44KHz - software default

•Sample format - number of bits representing

each sample - 16, 24 or 32bits

•Compression - sophisticated methods used by

software to reduce file size

Recording Digital Software

A number of software applications are available

for sound recording and editing:

•Adobe Audition

•Steinberg Wave Lab

•Sony Sound Forge

•Apple Final Cut

•Creative Wave Studio

•Audacity

Audacity

Audacity is a free to use multi-track digital audio

application. It is a fully featured cross-platform

editor, mixer and recorder. It is available for

download at: 

http://audacity.sourceforge.net/download/ 

File Formats

Audio tracks can be imported into audacity in almost all

file formats. Files can be saved in the following

formats:

•Audacity project format (aup) - Audacity default.

Opens and closes files very quickly.

Incompatible with all other audio software. Used

during project creation (multi-track). Finished

project is then saved to another file format.

File Formats

•Windows wave format (wav) - Windows default.

An uncompressed format.

•Audio interchange file format (aif) - Apple MAC

default. It is also uncompressed.

• MPEG3 (mp3) -uses compression (up to 10:1).

Audacity can import MP3, but a plug-in is necessary

to export MP3.

•Ogg Vorbis (ogg) - Alternative to MP3. Similar

compression - better quality. Patent free.

Audacity Interface

Control Toolbar Mixer ToolbarMeter Toolbar

Edit Toolbar Selection Toolbar Track Window

Opening Sound Files

When Audacity is opened, the work area is empty.

Audio files can be opened in audacity in the

following ways:

•File menu, Open - for single track editing

•Project menu, Import - for multi-track editing

Toolbars

File menu - open and save projects

Edit menu - select and edit audio tracks

View menu - zoom controls

Project menu - add tracks to a project

Generate menu - generate noise, silence

Effects menu - add fade, remove noise and clicks etc.

Analyse menu - advanced tools - find the beat etc.

File Menu

Control Toolbar

Control Toolbar

Editing tools Audio control tools

The control toolbar is divided into two sections:

•Editing tools - zoom, select and edit tracks:

•Audio control tools - control the recording and

playing of audio tracks or projects

Edit Tools

Selecting tool - select a track/portion of a track.

The selection tool is used to select a portion at the end of the

Tank.wav waveform. The Fade Out command - Effects menu is

used and the result is seen below. Instead of a sudden end to the

sound, it will fade to silence over the selected time.

Edit Tools

Samples

Draw tool - The draw tool is used for modifying individual

samples within the waveform. The waveform must be zoomed

sufficiently to see the samples as dots along the profile.

Below, the Tank.wav track is zoomed to show individual

samples. The samples can be dragged to new positions as shown

below.

Edit Tools

Envelope tool - used to change the volume of a waveform or a

selection from a waveform.

When the tool is chosen, blue lines appear above and below the

waveform. By clicking the blue line at points, the waveform

amplitude can be increased or decreased. with the corresponding

reduction or increase in volume.  

Edit Tools

Time shift tool - used in multi track mode to move tracks

relative to each other.

Move the cursor to the beginning or end of the track and the cursor

changes to the double-arrow to indicate time shift. Drag the track

to the required position relative to the other track(s).

Edit Tools

Zoom tool - used to zoom in and out of a waveform. The left

mouse button zooms in and the right mouse button zooms out.

Zooming if necessary when editing a waveform.

Multi tool - gives access to the other five editing tools automatically

depending on the location of the cursor:

•Move the cursor over the ruler and it changes to the zoom tool

•Move the cursor to the beginning or end of the waveform and it

changes to the time shift tool

•Move the cursor over the waveform and it changes to the

selection tool etc.

Audio Control Tools

Skip to start - moves the cursor to the beginning of the project.

Skip to End - moves the cursor to the end of the last track

Play - plays the project from the current cursor position. Shift +

Play loops (continuously plays) the

Record - starts recording a track from the current cursor position

Pause - temporarily stops recording or playback.

Stop - stops recording or playback

Mixer Toolbar

The mixer toolbar has three controls:

 

•The playback volume is the volume is used by the system to play

the audio file

•The recording volume is the volume at which the audio track is

recorded

Playback volume Input sourceRecording volume

Mixer Toolbar

The input source drop down menu is used to select the device used

for recording:

Microphone - a microphone connected to the pink jack

Line in - an external device connected to the blue jack

Stereo mix - anything played through the sound card in stereo

Mono mix - as above, only in mono

Edit Toolbar

The edit toolbar is a shortcut toolbar and is used to perform edits on a

selected waveform of part of a waveform.

 

Cut - removes the selected waveform or part of to the clipboard

Copy - copies the selected waveform or part of to the clipboard

Paste - pasts the contents of the clipboard at the current cursor position

Trim - removes the area outside the current selection

Silence - adds silence to the current selection

Undo/Redo - as in any application

Zoom - plus, minus, fit selection in window and fit project in window

Meter Toolbar

The meter toolbar monitors the input and output levels.  

Playback meter is green, recording meter is red

L and R meters are for the left and right channels

Light areas show average levels, darker areas show peak levels

Peak lines to the right show the max level in the previous three seconds

Red lines at the extreme right show only if clipping is detected.

Clipping is where the audio is too loud and distortion has occurred.

Recording should be stopped and re-recorded at a lower level

Track Menu

Each track in a multi-track project will have a track drop-down menu.

The menu shows a series of commands that effect only the individual

track. The commands include:

Name - name or rename the track

Move track - move the track up or down the project

Mono - convert a stereo track to mono

Left channel - use the left speaker only

Right channel - use the right speaker only

Make stereo - joins two tracks into a stereo track

Split track - stereo track split into two mono tracks

Set format - 16, 24 and 32 bit format

Set rate - number of samples per second for

Selection Toolbar

The status area shows: 

•The current tool selected

•The current sampling rate

•The current selection

•Snap condition 

Preferences

Preferences are found in the Edit menu. There is an extensive

range of preferences, but only a few need be set.

•Quality tab - Sampling rate and the Sampling format are set

Preferences

•Audio I/O tab - the Recording and Playback devices ca be

set. These should be set to the system Sound Card in each

case. The number of channels used to record is also set

here. This will be mono or stereo.