Transcript Chapter 5 Capturing and Editing Digital Audio

Chapter 5
Capturing and Editing Digital Audio
“Computers and Creativity”
Richard D. Webster, COSC 109 Instructor
Office: 7800 York Road, Room 422 | Phone: (410) 704-2424
e-mail: [email protected]
109 website: http://pages.towson.edu/webster/109/
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Ways to Acquire Digital Audio
• Record
• Digitize analog medium
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Recording:
Hardware Requirements
• Computer with a sound card
– Almost all computers nowadays are equipped with a sound
card.
Sound card: converts the electrical signals into digital
format through sampling and quantization of the signals
• Microphone
– built-in the laptop
Usually does not produce sufficient sound quality
– external microphone
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Microphones
• Unidirectional
– Most sensitive to sound coming from the front
– Advantage: Ignore noise coming from the rear
• Omnidirectional
– Sensitive to sound coming from all directions
• If you don't have the specifications of a
microphone
– Place the sound source directly in front of the
microphone
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Recording:
Software Requirements
Digital audio recording program
• Also lets you edit audio
• Some common programs:
– Adobe Audition
– Sony Sound Forge
– Audacity (free, open-source)
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General Steps For Recording With a
Digital Audio Program
• Start a new file
• Specify settings:
– sampling rate
– bit depth
– number of channels
• If possible,
– run through or reherse the audio you want to record while
observing the sound input level
– adjust the sound input level so it stays below the red area
for the whole audio run-through
• Hit the record button to start recording, stop button to
stop
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Settings
• Sampling Rate
– 44,100 Hz: CD Quality
– 22,050 Hz: Sufficient for multimedia projects with voice over
and loop musics
• Bit Depth Setting
– 8-bit
• usually sufficient for speech
• in general, too low for music
– 16-bit
• for music
• Number of Channels Setting
– 1: mono
– 2: stereo
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Preferences Dialog in
Audacity
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Audio Level Meter in
Audacity
Input volume slider
Input level meter
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Microphone Level Adjustment in
Windows 7
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Microphone Level Adjustment in
Windows 7
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Microphone Level Adjustment in
Mac OS X
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Field/Outdoor Recording
• Voice recorder apps on cell phones:
– Not intended for high quality audio
– Usually mono
– File format: Lossy compression to produce smaller file
size suitable for email and uploading to Web from the
phone
– To transfer the audio to computer:
• Common method: Email it to yourself as attachment and
check your emails on your computer to detach the file
• iPhone: Can also use iTunes
• Android phones: Connect the phone to your computer as a
drive
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Basic Editing
• One audio at a time
– enhance audio (such as trimming, remove nosie)
even if it is for use in audio mixing
• Audio mixing with multiple audio
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One Audio at a Time
Basic workspace elements:
• Waveform display
– x-axis: time
– y-axis: audio amplitude
– mono: 1 waveform
– stereo: 2 waveforms on top of each other
• Transport controls (play, record, rewind, fast
forward buttons)
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Transport
controls
Audacity
waveform display
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Audio Mixing:
Working with Multiple Audio
Example applications:
• mix multiple instrumental playback where
each is recorded as a separate audio
• compose audio with multiple clips
• voice-over with background music
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Audacity
track 1
track 2
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Audio Mixing vs.
Recording Everything All Together
Record audio clips
separately and mix them
later
Record everything all
together at once
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Advantage of Audio Mixing
• Allow you to adjust the volume level and apply
effects (such as fade-in and fade-out) to each
audio independently
• Examples:
– You can adjust relative volume of the voice-over and
the background music if you record the voice-over and
background music as two separate audio.
– You can insert a silence in the voice-over if needed for
controlling the timing.
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Parallels between Basic Digital Image
and Digital Audio Editing
Basic Digital Image Editing
Basic Digital Audio Editing
Reassemble image content by cutting,
copying, and pasting
Reassemble audio waveform by cutting,
copying, and pasting
Adjust tonal value
Adjust volume
Clean up dirt, dust, and scratches
Noise reduction
Resize the image
Resample the audio
Reduce the image’s color depth
Reduce the audio’s bit depth
Apply filters for special effects
Apply filters for special effects, such as
reverb and pitch changes
If you want to save your file as JPEG for
the Web, wait until the last step because
JPEG uses lossy compression
If you want to save your file as MP3 for
the Web, wait until the last step because
MP3 uses lossy compression
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Reassembling Waveform
• To select a segment of a waveform:
Click-drag to select
• You can cut, copy, or delete the selection
• To paste a segment of a waveform:
– Click at position you want to paste
– Paste (Usually, Edit > Paste)
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Reassembling Waveform
Example
1
2
3
4
Original recording of saying: 1 2 3 4
The segment for "2" is selected
2
1
3
4
The segment for "2" is cut and pasted
before "1". Now, the audio says: 2 1 3 4
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Changing Volume
• When the original audio is too soft or too loud
for the intended use
• When composing multiple audio that do not
have a consistent volume level—some too soft
and some too loud
• When you want to fade in or out an audio
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Common Functions for
Changing Volume
• Amplify:
lets you specify amplification in a dB (decibels)
or percentage
• Normalize:
– lets you set a peak level for a file or selection
– amplifies the entire file or selection so that the
highest level is the peak level you specify
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Common Functions for
Changing Volume
• Fade in:
suppresses the volume at the beginning of the
audio
• Fade out:
suppresses the volume at the end of the audio
• Envelope:
– lets you use a curve to specify the ups and downs of
the volume over the course of the audio
– can create fade-in and fade-out effect
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Noise Reduction
Useful for removing background noises, such as:
• computer fan noise
• hissing noise of the microphone
• To reduce noise that is constant throughout
the audio
• The noise may contain wide ranges of
frequency
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Noise Reduction
How it Works
• You select a segment that contains pure noise.
• The program performs a statistical analysis of
the noise to generate a profile.
• The program reduces the noise of the whole
audio (or selected segment) based on the
noise profile.
• Audacity: Noise Removal
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Special Effects
• Change of pitch
– chipmunk voice (higher pitch)
– Darth Vader voice (lower pitch)
• Change of speed
– helium voice (faster speed)
– slow-motion voice (slow speed)
• Reverb
Create the feel from being in a large empty
auditorium to a small bathroom.
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File Size Consideration
• Best to record and work with audio at CDquality levels (i.e., 44,100 Hz sampling rate,
16-bit, and stereo) or higher
• When delivering the final audio, depending on
the project, you may need to lower the file
size:
– downsample the file to lower the file size
– export to MP3
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Types of Music Creation
• MIDI:
– create original music scores
– require musical composition skills
• Loop music composition
– compose a long musical audio through repetitions of short
musical clips
– common in projects that do not require a long musical
score, for example:
• game development, product advertisements, digital art projects
– allow non-music composers to create musical audio
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MIDI
•
•
•
•
Not sampled audio
Like sheet music
Constains instructions for recreating the music
Created by editing music notations and instrument
assignments
• Can also be created by recording your performance on
a MIDI keyboard connected to a computer
• Playback of a MIDI file requires a sound card that uses
the synthesizer to recreate the sound of notes
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MIDI Playback
• Requires a sound card that uses the
synthesizer to recreate the sound of notes
• Not all synthesizers produce the same sound
• Disadvantage: How the music actually sounds
during playback depends on the sound card
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Loop Music
• Music that is created from short music clips
that are repeated
• Usually designed to loop seamlessly
• Libraries of clips for loop music are
commercially available
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Composing Music Using Loop Music
• Programs support multi-track
• Import an audio clip to place on a track
• Create repetitions of a clip placed on a track
simply by dragging its right edge to extend it
• You can adjust the volume of each track to
fade in or out the clips
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Uses of Digital Audio
•
•
•
•
•
Video
Multimedia authoring
Playback on the Web
Audio CD
Podcast
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Video and Multimedia Authoring
• Export audio and import it into the video editing or
multimedia authoring program
• Most video editing program support:
– .wav
– .aif
– mp3
• Adobe Flash supports:
–
–
–
–
–
.wav
.aif
.au
.mp3
audio-only QuickTime
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Playback on the Web
• Best if small file size for less wait time
• HTML5 audio
• Streaming format
• Progressive download
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Methods to Play Back on the Web
• Embedding the audio on the Web page
– HTML5 audio
Played using the browser's built-in player
– Non-HTML5 audio
Played using plug-in or external player
• Linking to the audio file
– will cause the file to play in an external player
window
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HTML5 Audio
• Supported formats: MP3, ACC (MP4), OGG
Vorbis, and WAV
• HTML5 <audio> tag:
Example usage:
<audio src="demo.oga" controls>
• An introduction of HTML5 video and audio is
covered in Chapter 15
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QuickTime Audio-Only Movies
• Can be exported using video-editing programs
(Adobe Premiere Pro, Apple Final Cut Pro)
• Fast-start movies:
Allow progressive download—the audio will
start to play as soon as enough data have
been downloaded.
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RealAudio
• Can be streamed
– require a Real Server—a streaming server
• Can also be used on the Web without
streaming
• .ra or .rm file
– converted from a .wav using RealProducer Basic
(free) or RealProducer Plus
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Audio CD
• Must use:
– sampling rate: 44,100 Hz
– bit depth: 16
– stereo
• Audio editing programs (such as Adobe Audition)
also let you create audio CD projects:
–
–
–
–
title and artist for each track
length of pauses between tracks
enable/disable copy protection
ISRC number
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Podcast
• Podcast:
– a collection of files available on a Web server
– usually audio files
– can be any types of files: Web pages, text, PDF, images, ...
• Episode:
– Each file in the podcast
• Feed:
– The text file that lists the internet addresses of the files in
a podcast.
– Posted on a Web server
– People subscribe to the feed
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How Podcast Works
• Whenever a new episode is available, it will be
automatically downloaded to the subscriber's
computer or device (e.g. iPod)
• The software program that periodically checks
and download the new items is called
aggregator (e.g. iTune)
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