Chapter 5Capturing and Editing Digital Audio

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Ways to Acquire Digital AudioRecordDigitize analog medium

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Recording:Hardware RequirementsComputer 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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MicrophonesUnidirectional

◦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 RequirementsDigital audio recording programAlso lets you edit audioSome common programs:

◦Adobe Audition◦Sony Sound Forge◦Audacity (free, open-source)

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General Steps For Recording With a Digital Audio ProgramStart a new fileSpecify 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-throughHit the record button to start recording,

stop button to stop

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SettingsSampling Rate

◦ 44,100 Hz: CD Quality◦ 22,050 Hz: Sufficient for multimedia projects

with voice over and loop musicsBit 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 inAudacity

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Audio Level Meter inAudacity

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Input level meterInput volume slider

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 RecordingVoice 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 EditingOne 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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Audacity

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Transport controls

waveform display

Audio Mixing:Working with Multiple AudioExample 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

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track 1

track 2

Audio Mixing vs. Recording Everything All Together

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Record audio clips separately and mix them later

Record everything all together at once

Advantage of Audio MixingAllow 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 EditingBasic 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 21

Reassembling WaveformTo 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 WaveformExample

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Original recording of saying: 1 2 3 4

The segment for "2" is selected

The segment for "2" is cut and pasted before "1". Now, the audio says: 2 1 3 4

1 2 3 4

2 1 3 4

Changing VolumeWhen 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 forChanging VolumeAmplify:

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 forChanging VolumeFade 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 ReductionUseful for removing background

noises, such as:computer fan noisehissing noise of the microphoneTo reduce noise that is constant

throughout the audioHiss Reduction: If the audio amplitude

within a certain frequency range falls below the threshold, the audio of that range will be greatly reduced.

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Noise ReductionHow it WorksYou 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 Reduction Profile.

Audacity: Noise Removal28

Special EffectsChange of pitch

◦Chipmunk voice (higher pitch)◦Darth Vader voice (lower pitch)

Change of speed◦Helium voice (faster speed)◦Slow-motion voice (slow speed)

ReverbCreate the feel from being in a large empty auditorium to a small bathroom.

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File Size ConsiderationBest to record and work with audio

at CD-quality 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 CreationMIDI:

◦ 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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MIDINot sampled audioLike sheet musicContains instructions for recreating

the musicCreated by editing music notations

and instrument assignmentsCan also be created by recording

your performance on a MIDI keyboard connected to a computer

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MIDI Producing with Logic Pro X

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MIDI Producing with Cubase

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MIDI PlaybackRequires 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: device dependent.

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Loop MusicMusic 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 MusicPrograms support multi-trackImport an audio clip to place on a

trackCreate 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 AudioVideoMultimedia authoringPlayback on the WebAudio CDPodcast

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Video and Multimedia AuthoringExport audio and import it into the video

editing or multimedia authoring programMost video editing program support:

◦ .wav◦ .aif◦ mp3

Adobe Flash supports:◦ .wav◦ .aif◦ .au◦ .mp3◦ audio-only QuickTime

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Playback on the WebBest if small file size for less wait

time

HTML5 audio

Streaming format

Progressive download

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Methods to Play Back on the WebEmbedding the audio on the Web

page◦HTML5 audio (simple audio tag included)

Played using the browser's built-in player

◦Non-HTML5 audioPlayed 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 AudioSupported 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 MoviesCan 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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RealAudioCan 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 CDMust use:

◦ sampling rate: 44,100 Hz◦ bit depth: 16-bit◦ 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 (International Standard Recording Code)

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PodcastPodcast:

◦ 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 podcastFeed:

◦ 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 WorksWhenever 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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