Technology ICT Option: 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 Time Amplitude

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 Time Amplitude

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 Selection Toolbar Track Window Edit Toolbar Control Toolbar Meter Toolbar Mixer Toolbar

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 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.

Control Toolbar Control Toolbar 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 Editing tools Audio control tools

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 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. Samples

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 source Recording 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 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.