Multitrack audio and creating MP3 podcast files: Podcasting for E-Learning

Today's post about Podcasting for E-Learning covers editing and rendering multitrack audio using the open-source audio editor Audacity.

Click on the play button on the YouTube video to view the demo at 240x320 size (which will give you an overview of the editing techniques I'm using), or click here to view the demo (1024x768, broadband connection recommended) to see the editing techniques in detail. The demo is about seven minutes in duration, and requires Flash Player version 7 or better.

Typically, a podcast has a number of discrete audio tracks:

• Musical signature tune track
• Narration voice-over (v/o)
• Incidental music and / or wildtrack (ambient sounds such as keyboard taps, phones ringing etc)

To create, edit and render a multitrack audio file (called a 'package'):

1. Open and save a new Audacity project
2. Name it something like 'My_Podcast_Final'
3. Using the File menu, open the first track to be played in the sequence (usually the sig tune)
4. Using the Project >> Import Audio menu add the rest of your clips. Each clip will open on a new track in the Audacity UI
5. Using the Timeline Shift Tool to move the new tracks to their approximate location on the timeline; you'll refine their location later
6. Use the Envelope Tool to set the volume at appropriate levels for cross-fades, fade-ins, fade-outs, and for setting music as a soundbed under the voice-over narrative
7. When you have all the elements of the package aligned to more-or-less where you want them, use the Timeline Shift Tool to refine the timing of the various elements - try to make the clips as "tight" as possible: omit any long silences or caesurae unless they're for dramatic effect.
   If your audience hear a long silence they may well think that they have reached the end of the package and turn off.
8. Once your package is edited satisfactorily, save it.
9. Next go to File >> Export as MP3
10. Enter appropriate metadata in the dialog box and click on Save.
11. An MP3-formatted version of your project file is rendered according to the settings entered in the Preferences tab.
12. You're done!
13. Make a cup of your favorite hot beverage
14. Open the audio package in your software media player. Sit back and listen to your completed magnum opus.
15. Start thinking about a topic for your next podcast, which will be even better than this one!

More...
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Demonstration: Editing an Audio File. Podcasting for E-Learning

Today's post is a demonstration describing how to edit an audio file using the Audacity open-source non-linear sound editor.

Click on the play button on the YouTube video to view the demo at 240x320 size (which will give you an overview of the editing techniques I'm using), or click here to view the demo(1024x768, broadband connection recommended) to see the editing techniques in detail. The demo is about six minutes in duration, and requires Flash Player version 7 or better.

Now, some context: in my previous post in this series about Podcasting for E-Learning, I described the pre-edit stage of post-production.

In that post I discussed audio has been recorded, the master file was saved and imported into your audio editor. Next I described how the sound file was to be “cleaned up” by ensuring the file was:

1. Topped & tailed
2. Normalized
3. NRed
4. EQed
5. Saved as an "_edit" version.

Now, you can actually edit the audio content.

Broadly speaking, this means applying edits to remove “umms,” and “ahhs,” coughs, bad (or repeated) takes, clicks, pops, and bangs – there will be many!

Today’s demonstration is a section of the master file from my E-Learning Curve Podcast episode Flash and Captivate. In this section of the narrative, I'm discussing the Flash format and its uses. In the demo I undertake the follow activities:

1. Open the ‘_edit’ file
2. Play back the narrative to understand what edits need to be made (the clip is about 15 seconds in duration)
3. Make a note of the edits to be made (see bullets below)
4. Use various Audacity controls including the Rewind and Play buttons, Selection, Envelope and Zoom Tools, and the Crossfade Out effect to make edits in the file
5. Play back the complete narrative with edits implemented (about 13 seconds in duration)
6. Save the edited file

The master file includes the following elements to be modified or elided:

• One repeated phrase
• Two audible inhaled breaths
• A series of small audible oral clicks
• One large audible oral click
• Noise at the end of the clip

More...

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Podcasting for E-Learning: Recording with Audacity

Having given you the ha'penny (or dime) tour of Audacity, it's time to talk about recording audio with a digital editor. Figure 1 describes the end-to-end audio production process. Today, I will look at steps 1 through 5:

Figure 1. Audio Production Process
[Click to enlarge]

And these are the steps in detail:

Activity	Requirement
Audio source	A Narrator
Capture	A Microphone
Encoding	Audio editing software Audacity Sound Forge WaveLab GarageBand

Once you have your narration script, your mic, and your audio-enabled computer you may begin recording.

You Try:

1. Launch Audacity
   
   
2. In default configuration, a new, empty project will open. Save this project to a location of your choice. Call it MyPodcast (or whatever name you choose). This saved project becomes the "holder" for all of your recorded and imported sound clips.
   
   
   Remember, that if you don't save your project before you start recording, all recordings, edits and other files will be written to the default directory set on the Directories tab of the Preferences dialog box.
   
   
3. Check the Preferences
   
   Confirm that your desired playback and recording device are set. If you're going to record a mono signal, set the number of recording channels to 1 (Mono) on the Audio I/O preferences dialog box.
   
   When picking a device to record from, make sure you've set up all the connections correctly, including plugging a microphone in to the computer microphone input. Since most soundcards mix the inputs back in to the outputs, the easiest way to test your microphone is to speak in to it while playing with your sound card mixer. The sound card mixer is a piece of software either provided by the sound card maker, or by the operating system you're using.
   
   The Windows mixer is quite straight-forward, though some soundcards use their own custom mixing panel. The Mac's mixer is controlled via the Sound Control Panel, and Linux users can choose from a variety of mixer applications. Set the signal input to the desired level. I recommend setting the volume to about 80 per cent of maximum. This ensures you have enough ‘headroom’ to capture variations in tone and amplitude without distorting the signal from the microphone.
   
   
4. Begin recording
   
   - The red Record button initiates recording.

   - The blue Pause button pauses the recording. Click on the button again to continue recording.

   - The yellow Stop button finishes the recording process for the clip you're capturing.
   
   Well done: you have made your first audio recording in Audacity! You can now manipulate your recording and explore the editing capabilities of Audacity.
   
   More…
   
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Podcasting for E-Learning: Setting Audacity Preferences

Setting Audacity Preferences on Your Computer

Before beginning a recording project in Audacity, it's necessary to configure your version of Audacity’s preferences in the Edit Preferences dialog box. This ensures that the sound source and playback options are set correctly as well as bit-rate, quality indicators and so on. Follow this step-by-step procedure to configure Audacity for your computer and operating system.

Configuring Audacity

You Try

1. Launch Audacity
2. Check the Preferences.
   Checking the Audacity preferences is very important step and should be done before you begin editing any audio. You can locate the Preferences Dialog box by going to Edit Preferences, or the shortcut key combination CTRL+P.
   
3. Set Audio Input & Outputs.
   Select the Audio I/O tab from the choices across the top of the Preferences Dialog box. I/O is short for Input Output and is where you’ll tell it to record your sound from and where to play it back.
   
4. Set Playback Output.
   
   
   From the Playback Device: drop-down menu, select the output device that you would like to route the sound through. In this case, I’m sending the signal via my internal PC sound card.
   
5. Set Recording Input.
   
   
   From the Recording Device drop-down list, select the sound source you want to record from. In this case, I’m selecting the SigmaTel sound card, which takes input from the microphone that I’m going to use to record some voiceover narration.
   
   
   If you’re recording music, select the Record in Stereo check box. If you’re just recording voice-over narration, leave it unchecked. Similarly, uncheck the "Play other tracks while recording new one” option (unless you’re Les Paul or Mary Ford).
   
6. Sound Quality Tab.
   
   
   The Quality tab is where you’ll set the quality of your audio. The higher the sample rate, the better quality your audio, but the larger the file size will be. For CD quality sound, record at 44,100 Hz. You’ll typically leave the other settings at their factory defaults.

More…

Podcasting for E-Learning – Tour of Audacity’s User Interface

In my previous post, I discussed interface metaphors, and showed a video example of the process behind the analog tape-editing metaphor used by most media editing tools - including Audacity. Today, I will describe how this approach to editing is replicated virtually, via your computer's user interface. Figure 1 shows the primary menu options and functions of Audacity.

Figure 1 The Audacity UI
[Click to Enlarge]

The menu bar contains all of the functions for Audacity.

Figure 2 The Audacity Menu bar
[Click to Enlarge]

You’ll see some familiar features – Open, Import, Copy, Cut, Paste, and so on. There are also a range of audio-specific functions including the facility to analyze the audio signal, generate white noise, a pure note tone, or a click track, as well as a range of audio effects including:

• Noise reduction (NR) to remove background noise
• Normalization (increasing or decreasing the amplitude of an entire audio signal so that the peak amplitude matches a desired target. Typically, normalization increases the amplitude of the audio waveform to the maximum level that does not introduce any new distortion – this “makes the audio louder”
• Equalization (EQ) - changing the characteristics of the audio – i.e. add bass or treble, cut or enhance certain frequencies

The features of the Audacity timeline (see Figure 3) are common across all audio editors.

Figure 3 The Audacity Timeline
[Click to enlarge]

1. The label track enables you to insert information about events on the timeline. Here, I have indicated the point where the intro music begins, and the point where the first voice-over should start.
2. Most important is the audio waveform itself. The waveform is a graph showing the amplitude (loudness) of the audio signal over time.
3. The track controls allow you to control the characteristics of an individual track on the timeline.

There are two types of audio file in Figure 3: a stereo file which is typically used for music, and a mono file, which we use for narration. There is little point recording voice-overs in stereo – you only have one voice (or audio source), after all. If you record a voice-over in stereo, you only double the file size, for no gain in quality.

Using Audacity

These are the Rules of Audacity (according to SourceForge.net)

• One audio clip per track.
  An audio clip is simply a piece of audio material, imported, recorded, split or duplicated from another track, one track can only carry one piece of audio at a time. You can extend it by pasting material or inserting silence in to it, or cut a piece away, but it will always be one continuous piece of audio.
• Audacity always records to a new track.
  This new track is opened at the lowest free track. You'll can zoom out and then resize the track view of the lowermost-most track to see what is recorded. You can actually use the window sliders at the bottom and right to do this after starting to record, but this way no performance will be lost to the windowing system.
  Pressing CTRL+F displays all the tracks in your entire project. Note: this function only affects the horizontal zoom (left-right zoom); you must use the mouse and the magnifying glass icon to zoom out .
• Edit/Duplicate will not create a new audio file.
  This may not seem important, but it is useful to know this if you're editing a large recording. Audacity is a non-destructive editor (unlike the analog editing process): it works by referencing the original (or master) audio material: edits and other change you make affect the referenced file, not your master file.
  
  One of the positive consequences of non-destructive editing is that you can undo/redo edits as many times as you need to even after you have saved your project, which is pretty cool.

Next Time: Setting Audacity Preferences

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Podcasting for E-Learning: Audio Editing + Audacity

Previously in this series of E-Learning Curve Blog posts about Podcasting for E-Learning, I discussed downloading and installing the open source audio editor called Audacity. I chose Audacity because it’s free (as in speech), it’s available for Linux/Unix, Mac OS and various Windows operating systems, and most importantly, it’s a very impressive media editing tool.

If you’ve taken the time to install and run the app you should see something similar to Figure 1: this is the Audacity audio editor user interface (UI) in Windows XP.

Figure 1. The Audacity User Interface
[Click to enlarge]

If you’re not familiar with digital media production, this type of UI can seem quite daunting, and even alien. Today, I’m going to begin normalizing this new environment for you.

Now read on…

I’ll begin by taking a step back for a moment: let’s discuss interface metaphors.

An interface metaphor is a set of unifying concepts used by a computer graphical user interface to help users more easily interact with the computer. The interface metaphor treats the monitor of a computer as if it is the user's desktop, upon which objects such as documents and folders of documents can be placed. A document can be opened into a window, which represents a paper copy of the document placed on the desktop. Since it was first developed at Xerox PARC in 1970, the desktop metaphor has been extended and stretched, so that items not found on a 'real' desktop (like a trash can) are now displayed onscreen.

In this context, we can say that pretty much all digital editors have an interface metaphor based on analog tape editing procedures: the waveform (see Figure 2) represents the magnetic tape, and the transport bar (Play, Pause, Stop buttons, and so on) represents an analog tape recorder's transport controls, for example. Similarly, there are Cut, Splice and digital sound effect features and functionality that replicate these processes in the analog world.

Figure 2. Some Audacity features and functions
[Click to enlarge]

In my view, the most effective way to demonstrate these concepts is through an example. In this YouTube video, Rod Summers demonstrates how to edit a piece of analog magnetic tape.

The Scenario:

The source audio is a short piece of recorded voice-over of the presenter counting from one through ten. He has transposed "six" and "five" in his narration. This demonstration outlines the process for correcting the error.

Here are the steps in the process:

1. The editor cues up the tape by using a technique called "scrubbing"
2. He marks the In- and Out points for the edit...
3. And he marks the insertion point for the edit
4. Next, he makes the edit by physically cutting the tape and splicing the join...
5. Before inserting the cut piece of tape into it's new position
6. Finally, the edited tape is played back to test the verify the edit
   
   

Next time: I will look at editing in a digital environment ...and don't worry, this is a much easier undertaking when using a tool like Audacity!

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Podcasting for E-Learning: Editing and Producing Podcasts

So far in this series of posts about Podcasting for E-Learning from the E-Learning Curve Blog, I've covered a lot of material, including:

• A Brief History of Audio in Education
• The Four 'P's' of narration
• Introduction to Audio Production
• Digital Audio Basics

Now, it's time to look in some depth at editing and producing podcast content.

As I discussed last time, non-linear editing applications are media editing tools which can randomly access the source material - and that’s it. You don’t have to edit audio in a beginning-middle-end sequence. You can also drop in new files, split audio, modify the volume (or amplitude), “top and tail” the recording, and add effects, before generating a rendered file which contains all of the modifications you made to your audio.

Non-linear editing enables the editor to access any frame in an audio clip. It can be viewed as the audio equivalent of word processing, which is why the process is often called desktop editing. Typically, audio is either recorded directly to a PC hard drive, or is imported from another source, in the same way as that text is either authored within the a word processor application, or a file is imported from another location.

In non-linear editing, the original source files are not lost or modified during editing. This means that you can easily make changes and cuts, experiment with the audio, and undo previous decisions secure in the knowledge that you are not interfering with the original - or master - files. Loss of quality is also avoided as you don't have to repeatedly re-encode the audio when different effects are applied.

While there are many excellent commercial, free-to-use, and open source audio editing applications applications available, the editor I will talk about during this series is called Audacity.

Audacity is an open source, easy-to-use multi-track audio editor and recorder for Windows, Mac OS X, GNU/Linux and other operating systems. You can use Audacity to:

• Record live audio.
• Convert tapes and records into digital recordings or CDs.
• Edit Ogg Vorbis, MP3, WAV or AIFF sound files.
• Cut, copy, splice or mix sounds together.
• Change the speed or pitch of a recording.

So, let's download and install Audacity.

You Try:

1. Navigate to the Audacity download page and select the download for your operating system.
   
   
   
2. Click on the appropriate link. This will take you to the SourceForge download page - don't "save link as.." or "save target as..".
3. The SourceForge download should start automatically. If it does not, click the links in the black panel marked "direct link" or "mirror". Only these links and the automatic download are authorized versions of Audacity. Disable any automatic download managers if the download is incorrect.

I also recommend that you download these optional files:

• LADSPA plugins 0.4.15 installer (.exe file, 1.5 MB) – nearly 100 audio digital effects plug-ins
• LAME MP3 encoder - Allows Audacity to export MP3 files

System Requirements: Windows-based Systems

The values in the "Recommended RAM/processor speed" column below are for tasks like recording for an hour, or editing three 20 minute tracks simultaneously. The values in the "Minimum RAM/processor speed" column will be fine for smaller/shorter tasks, especially if unused programs are closed.

Windows version	Recommended RAM/processor speed	Minimum RAM/processor speed
Windows 98, ME	128 MB / 500 MHz	64 MB / 300 MHz
Windows 2000, XP	512 MB/1 GHz	128 MB/300 MHz
Windows Vista Home Basic	2 GB / 1 GHz	512 MB / 1 GHz
Windows Vista Home Premium/Business/Ultimate	4 GB / 2 GHz	1 GB / 1 GHz

Audacity works best on computers meeting more than the minimum requirements in the table above. Where Audacity is to be used for lengthy multi-track projects, Audacity's developers recommend using Windows 2000, XP or Vista running on machines of substantially higher specification than the minimum specs outlined above.

Apple Macintosh

Installation instructions (MacOS 9 and OS X):

1. Inside your Applications folder, create a folder called "Audacity"
2. Double-click the downloaded .dmg to mount it
3. Option-drag the whole of the .dmg contents (not the .dmg itself) into the "Audacity" folder you created
4. Double-click Audacity.app inside the Applications folder to launch it

Mac OS X version	Audacity Version	Recommended RAM/processor speed
Mac OS X 10.1	Audacity 1.2	64 MB / 300 MHz
Mac OS 9.0	Audacity 1.0	64 MB / 300 MHz

Linux/Unix

Audacity's developers recommend using the latest version of Linux/Unix from your distribution that is compatible with your hardware specifications. Audacity will run best with at least 64 MB RAM and a 300 MHz processor.

Installation packages for Audacity on GNU/Linux and other Unix-like systems are often provided by individual distributions:

• Alt Linux
• Debian
• Fedora Core
• Fedora Project
• Mandriva i586
• OpenSUSE
• Red Hat
• SuSE and packman (suse)
• Ubuntu: packages.ubuntu and rpm.seek

This list is not comprehensive. If you don't see an up-to-date package for your distribution, search your distribution's web site for the latest information. Alternatively, you can compile Audacity from source code.

More…

New E-Learning Curve’s Other Podcast new episode release:

Transatlantic: The Flying Boats of Foynes. The Complete Podcast Documentary.

It's the 70th anniversary of the first scheduled trans-Atlantic air passenger service, which opened in July 1939. Told against a backdrop of the momentous events of World War II, this podcast documentary tells the story of the town of Foynes on the River Shannon in Ireland, which served as the western European base for the majestic flying boats of Pan Am, Imperial Airways and other airlines in the Golden Age of Aviation.

From their proving flights in the late 1930's through World War II and into the post-war period, Chief of Launch Operations at Foynes recalls his time working for Imperial Airways, and the effect of this glamorous mode of travel on a small Irish port. Even today, airplanes like the Catalina, the Short Empire class, and the majestic Boeing B-314 Clippers speak of a time now long gone.

Click on the link to celebrate the memory of the age, and the life and times of those who lived it.

Click here to listen to the podcast (MP3, 28MB).

Click here to listen to the podcast on iTunes.

Click here to view the transcript of this podcast (PDF, 585K).

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Podcasting for E-Learning: Digital Audio Basics

Really exceptional podcasts transmit a sense of "being there."

Well-designed, planned, narrated and produced audio content has the facility to engage the audience and transport the listener, providing the right cognitive environment for learning or entertainment or whatever goal the podcast seeks to achieve. As the old story goes, “there are better pictures on the radio.” Denis Nowlan, Deputy to the Controller for BBC Radio 4 describes this as

the wonder of radio [and sound] …the conjuring of magical sounds, Prospero-like, out of the silently teeming air. And the sense of joining, instantly, with a vast community of listeners.

(2005)

Of course, this cognitively experienced sense of “being there” is a completely artificial construct, none more so when you consider audio podcasting. The journey the podcaster takes us on is based on nothing in nature; that is, a narrative transmitted as binary data: electronically-mediated zeros and ones.

I will discuss this phenomenon in detail next time, but for now, read on…

Digital audio is actually very similar in concept to motion film, where a rapid series of still photographs make up a “motion picture.” Digital recording reproduces audio signals by taking many still “pictures” – or samples - of an audio waveform and then reconstructing the waveform for playback digitally (see Figure 1).

Figure 1. Digital Sampling of Audio Waveform
[Click to Enlarge]

In film, the number of still images (frames) we move through the projector per second improves the smoothness and quality of picture we see. Similarly, the size of the film's light-sensitive crystals in each frame determines the visual resolution of the image - and we all know movies look better in 70mm as opposed to the 35mm or 16mm film.

In digital audio, an analog signal is typically sampled 44,100 times a second. Each sample is created by taking a "snapshot" of the amplitude (or strength) of an analog audio signal at a particular moment in time. and converting that amplitude into a binary number.

The number of samples contained in each second of audio is called the sample rate. The greater the number of samples per second, the greater the resolution of the audio signal.

Let’s return to the film analogy: the faster the film rate through the camera, the better the ability of the film to pick up motion. For example, if you crank a film camera too slowly, then motion past a camera is not smooth since the frame rate does not capture enough frames in a given amount of time to stop the motion from appearing to jump or jerk - too much action happens in front of the camera "between frames" for the motion to appear natural.

Time for an example: The resolution of an audio CD is 16 bits and the sample rate is 44.1KHz. This means that the audio is sampled 44,100 times a second and a series of 16 zeros and ones is used to define the amplitude of the waveform at each of those 44,100 points.

This resolution – commonly called “CD Quality” and should be your baseline for recording a podcast. When recording voice-over narration, capture all of your audio at 16 bit, 44.1KHz, in mono using the WAV format in Windows, Au format for Unix-based systems (like Linux), and AIFF for Apple Mac.

More...

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References:

Nowlan, D. (2005). Radio: where the pictures are better: Denis Nowlan speaks for the medium which leads you by the ear. [Internet] Available from: http://findarticles.com/p/articles/mi_m0KZH/is_1_19/ai_n15928065/ Accessed 12 August 2009.

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Open Environment E-learning 5: Audacity Audio Editor

Having discussed a range of primary design and authoring tools, today's post will look at one of the key content development tools, an open source non-linear audio editor (NLE) called Audacity.

[It] is an easy-to-use audio recorder and editor for Windows, Mac OS X, GNU/Linux, and other operating systems .

(sourceforge.net)

Audacity has the capability to record live sound, convert analogue media sources, and manipulate audio. Its functions include:

• Export to digital recordings like podcasts or CDs
• Edit WAV, MP3, FLAC, and Ogg Vorbis sound files
• Cut, copy, splice, and mix multiple audio files
• Apply a range of digital signal processes including normalization, noise reduction, EQ, and compression

Figure 1 Audacity audio NLE

Audacity enables audio content may be exported in a wide range of formats, making it an exceptionally flexible tool for content developers. With a relatively shallow learning curve, the application can be used by non-experts after a few hours on instruction and use, while retaining the features found in proprietary NLEs like Steinberg WaveLab and Sony Sound Forge for media developers .

This level of functionality enables both SME and specialist content developers to take advantage of the features in the application in an Open Environment for E-Learning.

References:

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Audacity website About Audacity [Internet] Available from: http://audacity.sourceforge.net/about Accessed 1 May 2008

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