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CSC 8610 & 5930 Multimedia Technology Lecture 5 Digital Audio Processing.

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Presentation on theme: "CSC 8610 & 5930 Multimedia Technology Lecture 5 Digital Audio Processing."— Presentation transcript:

1 CSC 8610 & 5930 Multimedia Technology Lecture 5 Digital Audio Processing

2 2 Today in class (3/12) 6:15Recap, Reminders 6:20Lecture – Digital Audio Repr. (cont’d) 7:00Digital Audio Processing 7:30Break 7:45Digital Audio Processing (cont’d) 8:15Project 1 proposal discussion, brainstorming 9:00Wrap

3 3 RECORDING

4 4 Ways to Acquire Digital Audio Record Digitize analog medium

5 5 Recording Requirements Hardware Software

6 6 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

7 7 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

8 8 Example Label of a Microphone

9 9 means unidirectional

10 10 If you don't have the specifications of a microphone... General Rule: Place the sound source directly in front of the microphone

11 11 Recording: Software Requirements Digital audio recording program Also lets you edit audio Some common programs: – Adobe Audition – Sony Sound Forge – Audacity (free, open-source)

12 12 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

13 13 Sampling Rate Setting Sampling rate examples: – 44,100 Hz: CD Quality – 22,050 Hz: Sufficient for multimedia projects with voice over and loop musics

14 14 Bit Depth Setting 8-bit – usually sufficient for speech – in general, too low for music 16-bit – for music

15 15 Number of Channels Setting 1: mono 2: stereo

16 16 Preferences Dialog in Audacity

17 17 Digitizing Analog Medium Connect the line-out port of your analog medium playback device to the line-in port on your computer Rehearse the playback of the analog medium to determine the best input level Start recording using digital audio recording program before start playing the analog medium

18 18 EDITING

19 19 Basic Editing One audio component at a time – enhance audio (such as trimming, remove noise) even if it is for use in audio mixing Audio mixing with multiple audio

20 20 One Audio Component 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)

21 21 Audacity Transport controls waveform display

22 22 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

23 23 Audio Mixing: Working with Multiple Audio Audacity: – Add audio track by choosing Project > Import Audio...

24 24 Audacity track 1 track 2

25 25 Audio Mixing vs. Recording Everything All Together Record audio clips separately and mix them later Record everything all together at once

26 26 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.

27 27 Spectral View Another representation of the digital audio in addition to waveform x-axisy-axiscolor waveform viewtimeamplitude-- spectral viewtimefrequency of the audio amplitude

28 28 Spectral View Useful in: analyzing the frequency range of the audio selecting the frequency range of the audio identifying audio distortion due to frequency anomaly

29 29 BASIC DIGITAL AUDIO EDITING

30 30 Parallels between Basic Digital Image and Digital Audio Editing Basic Digital Image EditingBasic Digital Audio Editing Reassemble image content by cutting, copying, and pasting Reassemble audio waveform by cutting, copying, and pasting Adjust tonal valueAdjust volume Clean up dirt, dust, and scratchesNoise reduction Resize the imageResample the audio Reduce the image’s color depthReduce the audio’s bit depth Apply filters for special effectsApply 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

31 31 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)

32 32 Reassembling Waveform Example Original recording of saying: The segment for "2" is selected The segment for "2" is cut and pasted before "1". Now, the audio says:

33 33 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

34 34 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

35 35 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

36 36 Noise Reduction Useful for removing background noises, such as: computer fan noise hissing noise of the microphone

37 37 Noise Reduction of Hissing Hissing noise is often characterized by a certain frequency range Basic idea of hiss reduction: Suppress the amplitude for the hissing frequency range

38 38 Noise Reduction To reduce noise that is constant throughout the audio The noise may contain wide ranges of frequency

39 39 Noise Reduction - How it Works You select a segment that constains 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.

40 40 Noise Reduction in Digital Audio Programs Audacity: Noise Removal

41 41 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.

42 42 File Size Consideration Best 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

43 43 General Steps of Digital Audio-Recording Touch-up 1. Noise reduction 2. Trimming 3. Adjusting volume level

44 44 DELIVERY

45 45 Uses of Digital Audio Video Multimedia authoring Playback on the Web Audio CD Podcast

46 46 Video Export audio and import it into the video editing program Most video editing program support: –.wav –.aif – mp3 Some audio editing program, such as Adobe Audition, let you import video – can synchronize audio with the video

47 47 Multimedia Authoring Export audio and import it into the multimedia authoring program Adobe Flash supports: –.wav –.aif –.au –.mp3 – audio-only QuickTime

48 48 Playback on the Web Best if small file size for less wait time Streaming format Progressive download

49 49 Methods to Play Back on the Web Embedding the audio on the Web page Linking to the audio file – will cause the file to play in an external player window

50 50 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.

51 51 Embedding QuickTime Audio-Only Movies in a Web Page HTML tag Parameters: – controller: visibility of the movie controller bar – loop: whether the movie loops playback – autoplay: whether the movie automatically starts

52 52 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

53 53 Embedding RealAudio in a Web Page HTML tag Parameters: – controls: which player controls will be displayed

54 54 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

55 55 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

56 56 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)

57 57 General Steps to Podcast Audio 1. Create Your Audio Content in MP3 2. Put Your MP3 Files on a Web Server 3. Create Your Podcast Feed File an XML file that lists these information of each episode: – title – internet address – author – description – length and type of the audio – publication date 4. Publish Your Podcast Feed – Post your feed file to a Web server and make a link to the feed file like you would post and link any other content. – Icons used for the link:


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