Encoding H.264 video using QuickTime Pro

You can export H.264 vide from QuickTime Pro in a number of ways. The simplest way is to use the iPod preset. This is perfect for creating iPod compatible files, but it gives you no control over any of the settings. You may want to tweak the settings a bit to suit your podcast, in which case you'll have to create your own encoding setting.

Using the iPod preset
Using the iPod preset is simple:

1. Open QuickTime Pro, and open the video to be encoded.

2. Choose Export from the File menu. This opens the Export window, shown in Figure 1


Figure 1: Export an iPod compatible video from QuickTime Pro using this preset.

3. From the drop-down menu, choose Movie to iPod (320×240).

4. Click Save. QuickTime Pro exports an iPod compatible H.264 video.

The only problem with using this preset is that it doesn't give you any control over any of the encoding options. You can't select a bit rate, a resolution, or anything else. Of course, it's guaranteed to work on an iPod, which is pretty handy. But the default bit rate is rather high, clocking in at over 800 kbps. This is fine for a short podcast, but if your podcast is longer than, say, 5 minutes, you're looking at a pretty serious download. You may want to dial the bit rate down to reduce the file size. To do this, you have to set your encoding settings by hand.

Encoding using custom H.264 settings
QuickTime also makes it easy to customize the encoding settings. There are a few more steps than using the iPod preset, but you have far more control over the output. Follow these steps:

1. Open QuickTime Pro, and open the video to be encoded.

2. Choose Export from the File menu. Again, this opens the Export window, as shown in Figure 2.


Figure 2: Here's how to get to the MPEG-4 video export settings.

3. Choose Movie to MPEG-4 from the Export drop-down menu.

4. Click the Options button to get to the video export settings. To begin with, this opens the MPEG-4 video settings, as shown in Figure 3.


Figure 3: Configure QuickTime MPEG-4 export video settings with this dialog box.

5. Select MP4 from the File Format drop-down menu.

Note QuickTime Pro defaults to MP4 (ISMA) for MPEG-4 output. ISMA stands for the Internet Streaming Media Alliance. Unfortunately the H.264 codec is not yet considered ISMA compliant (as of Fall 2006). This really doesn't mean anything. The H.264 codec is part of the MPEG-4 standard and will play back in any modern QuickTime player or iPod. For best quality, you should choose the MP4 option, not MP4(ISMA), so you can use the H.264 codec.

6. Choose H.264 from the Video Format drop-down menu.

7. Enter a bit rate for your file. Remember that the total bit rate is the video bit rate plus the audio bit rate.

8. Enter your screen resolution in the Image Size field. If you want iPod compatible files, choose 320×240.

9. Click the Video Options button to access the advanced encoding options. This opens the Advanced Video Settings window, shown in Figure 4.


Figure 4: Be sure to select Multi-pass encoding for the highest-quality results.

10. Choose Best Quality (Multi-pass) encoding mode, and click OK.

Note You may be wondering about the profiles restriction (Main versus Baseline) on this screen. In MPEG-4 encoding profiles define the "tools" that can be used to encode the video. Consequently these profiles also define the tools required to play back the encoded video. In this example, the Main profile provides more encoding tools than the Base profile. Since our goal is the highest quality video, we chose the Main profile.

The MPEG-4 standard is incredibly broad and frankly, not written in a way that a layman can understand. For a fantastic, concise, and fun-to-read explanation of the MPEG-4 standard, we recommend Damian Stolarz' Mastering Internet Video.

11. Now it's time to configure the settings for your audio. Select Audio from the second dropdown menu in the MPEG-4 Export Settings window. This changes the information displayed in the bottom half of the window from video settings to audio settings, as shown in Figure 5.


Figure 5: Configuring QuickTime MPEG-4 export audio settings

12. The first thing to choose is the audio codec you want to use from the Audio Format dropdown menu. In fact, the only codec offered for MPEG-4 encoding is AAC, which is just fine, because it offers great quality.

13. Next, select the desired bit rate from the Data Rate drop-down menu. A rate of 32 kbps should provide good quality.

14. If you're encoding spoken word content or want slightly higher fidelity, choose mono from the Channels drop-down menu.

15. The next available setting is the Output Sample Rate. This determines how much highfrequency information is contained in the final encoding. In general, the default setting works just fine. However, you can experiment with lowering the setting to get increased fidelity.

16. Finally, set your Encoding Quality to Best. This makes the encoding process take a little longer, but hey, your podcast is worth it.

17. Click OK to return to the Export menu, and then click Save to start the export/encoding process. You'll see the QuickTime Export progress window, shown in Figure 6, which gives you an idea how long the process will take. Depending on the length of your podcast, you may have time to grab a cup of coffee.


Figure 6: The QuickTime export progress window lets you know how long it's going to take.

Exporting MP3 audio from Audacity | Step by Step

Exporting MP3 files from Audacity is simple, if somewhat limited. You have to set your desired bit rate in the Preferences window before you export, because you aren't given an option to adjust settings when you export. Here's how to set your preferred bit rate:

1. Open Audacity, and open your podcast audio file.

2. From the Edit menu, choose Preferences, as shown in Figure 1. This opens the Audacity Preferences window.


Figure 1: Use this dialog box to configure Audacity's MP3 export settings.

3. Click the File Formats tab.

4. Select your desired bit rate from the bit rate drop-down menu in the MP3 Export Setup section.

5. Click OK.

After you set your bit rate in the Preferences window, choose the Export as MP3 option from the File menu. That's all there is to it. Audacity doesn't offer the ability to do mono MP3 encoding or VBR-based encoding. As long as you don't want to do anything fancy, Audacity is a perfectly good encoding option.

Step-by-Step Encoding Examples | Podcast

Now it's time to actually encode some files. This section demonstrates audio and video encoding using stand-alone encoders, editing platforms, and even iTunes. If your editing application isn't demonstrated, don't worry: It probably works much the same way. Let's start with iTunes, which really isn't an encoder, but it can do the job.

Tip You should always archive the high-quality version of your file so that you can re-edit or re-encode it later.

Encoding MP3 audio using iTunes
iTunes automatically encodes all imported audio. When you insert a CD and iTunes offers to import it, the audio bits are pulled straight off the CD and encoded into whatever format has been specified. The default setting is to encode using AAC. However, iTunes will also convert music in MP3 if you prefer, and will convert any file into an MP3 file. All you have to do is import the file into iTunes, and then convert it to MP3.

Setting MP3 encoding defaults
To use iTunes as an MP3 encoder, you have to set the default encoding to MP3. Follow these steps to set iTunes to import using the MP3 codec:

1. Open iTunes, and open the Preferences window by choosing Preferences from the iTunes menu (the Edit menu on a PC). You also can open this window using the keyboard shortcut Command+, (Ctrl+, on a PC).

2. Click the Advanced icon/tab, and select the Importing tab.

3. Select MP3 encoder from the Import Using drop-down menu.

4. Select your bit rate from the Setting menu. By default, the lowest setting offered is 128 kbps stereo. For most podcasts, this is a perfectly fine setting. If, however, you want to economize on your bit rate, you can adjust the settings by selecting Custom from the Setting drop-down menu.

5. Select a bit rate from the Stereo Bit Rate drop-down menu.

6. You can select a sample rate or leave this set to Auto. If your podcast ends up sounding a little crunchy or distorted, you can try lowering the sample rate to get better fidelity.

7. If you want a mono podcast, select Mono from the Channels drop-down menu.

Note If you select Mono encoding, the bit rate will be half of what you specified in the Stereo Bit Rate drop-down menu.

8. Click OK to close the Custom Settings menu, and then click OK to close the Preferences window. iTunes will now import files using the MP3 settings specified.

Importing and Encoding
To encode using iTunes, you must first import the file, and then convert the imported file. Importing couldn't be simpler:

1. From the File menu, choose Import.

2. Browse to find the file you want to encode, and click Choose (Open on PCs). The file is imported and is listed in your music library.

3. Find the file in your music library. Click it to select it, and then from the Advanced menu, choose Convert to MP3.

That's all there is to it! iTunes encodes it using the settings specified on the Importing tab of the Advanced menu. The iTunes music folder is easy enough to find, but if you want to encode to a specific location, you can change this setting in the General tab of the Advanced settings window.

Caution Be careful when you change your iTunes music folder; otherwise, you'll end up with your music library in two different folders. It's probably a good idea to change the music folder back to the default after you've finished your encoding.

FireWire & setting it

By far the easiest method of capturing video is via FireWire. FireWire (officially known as IEEE 1394, and also known as iLink) is a standard by which data can be exchanged at very high speeds using a special cable and a FireWire port. Most digital video (DV) format cameras include a FireWire port. In addition to data transfer, the FireWire standard includes the ability to control remote devices (such as a camera). This makes capturing video from your DV camera a snap.

Simply connect the camera to your FireWire port, and open your video-editing platform. Most video-editing platforms include some sort of built-in "import" or "capture" functionality. You can generally control the camera from within the application and specify what part of the tape you want to capture. If you want to capture the whole tape, just rewind and hit the capture button.

If your computer doesn't have a FireWire port built in, you can buy a FireWire card for less than $50. If your camera doesn't have FireWire built in, you can buy a digital video converter. Digital video converters take analog audio and video inputs, for example from your camera, and create a DV signal that is available on the FireWire port. An added benefit of digital video converters is that they work both ways, meaning you can send the output of your video editor to the FireWire port, and the digital video converter converts it back to an analog signal that can be displayed on a monitor for quality-assurance purposes.

FireWire settings
One of the advantages (some might say disadvantages) of digitizing via FireWire is that there really are no settings for you to adjust. The DV standard is hard-coded into the entire process. You'll always be capturing full screen, full frame rate, using the DV codec.

The DV codec is another advantage to capturing via FireWire. Digital Video (DV) is compressed as it is recorded, making DV files about 1/5 the size of uncompressed video files. This makes them easier to store and move around. The compression affects image quality, however, and is one of the reasons that DV isn't considered true broadcast quality. However, the ease of use and the price points of DV cameras are virtually impossible to argue with.

Capturing via FireWire isn't really capturing in the truest sense; it's really just transferring the file from your camera (or tape deck) to your computer, just like you'd transfer a file from one computer to another. Because it's just a file transfer process, the video on your computer is an exact copy of the information on your camera.

Transferring files via FireWire using iMovie: A step-by-step example
Like so many things in the MacOS world, transferring DV from your camera to your Mac is a snap. Follow these steps:

1. First, connect your camera to your Mac's FireWire port, and turn your camera on to the playback or VCR position.

2. Open iMovie.

3. iMovie automatically detects that you have a camera connected and opens in "camera mode" (see Figure 1).


Figure 1: iMovie automatically detects a camera connected to your Mac and opens in camera mode.

Tip In camera mode, the stop, play, fast forward, and rewind buttons control your camera. You can use these controls to find the portion of your tape that you want to import.

4. To begin the import process, click the Import button (or hit the spacebar). If the tape is already playing, iMovie starts importing video from that point. If the tape is stopped, iMovie starts tape playback and begins importing.

5. iMovie automatically breaks up the imported video into clips each time it senses a new scene. This can be very handy, but it also can be a problem if you're trying to import a pre-edited piece of video with multiple scenes. You can disable this feature. From the iMovie menu, select Preferences (or just hold down the Apple button and push the comma key). Select the Import tab, and then deselect the "Start a new clip at each scene break" option.

That's it! You can now drag your clips to your iMovie timeline and edit away.

White balancing: A step-by-step example

White balancing: A step-by-step example
You need a decent-sized piece of white cardboard to perform white balancing. Follow these steps:

1. Have your talent hold the white cardboard directly in front of her, where all the lights are focused. If it's a tight shot, she may have to hold it in front of her face.

2. Zoom in until the white card fills the entire shot.

3. Find your camera's white balance control, set it to manual, and then set the white balance. Most cameras have a button to push or a menu option to select.

4. Zoom back out, and behold your wonderfully balanced picture.

When your lighting situation changes, you should rebalance the camera. This is particularly important if you're combining footage shot outdoors with footage shot indoors. If your white balance is off, people's flesh tones shift slightly, as do the colors of their clothing (if they're wearing the same color). If you're unsure whether you should white balance, do it just to be sure.

White-balancing tricks
You can use non-white cards when white balancing your camera for a special effect. Non-white balancing cards come in two flavors: warm cards and cool cards. The process is exactly the same as detailed previously, but by using a non-white card to white balance, you can trick the camera into thinking white is something different, and the result is slightly skewed colors in your video.

Why would you want to do this? Well, warm cards have a slightly blue tint, and when the camera compensates for this, the result is a slightly warmer image. This may be appropriate for a very intimate podcast shot indoors, if you want to make the viewer feel cozy. Cool cards have a slightly orange tint, so the resulting image is slightly blue. You've seen the effect in car commercials or computer commercials, where you get a very cool, impersonal look. This may be appropriate for a technology video podcast.

The best way to find out what warm and cool cards do is to play around with them. If you don't want to shell out the money for the professional versions, you can try white balancing with different shades of cardboard purchased at a local art supply store. But be careful; if you want a subtle effect, you want cards that are every so slightly off-white.

Exposure
After you set the white balance, you have to set the exposure. Many cameras have automatic exposure circuitry. However, much like the auto-focus mechanisms discussed in the preceding section, this feature often can be more trouble than it's worth.

Automatic exposure, sometimes called auto-iris, determines the exposure by the amount of light coming into the lens. The problem is that the amount of light, particularly outdoors, is continually changing. While it may seem like a good idea to adjust the exposure, it's distracting when the exposure changes in the middle of a scene.

Going back to the sailboat example in the preceding section, a sailboat with a big white sail coming into a scene dramatically changes the amount of light coming into the lens. To compensate, the camera changes the exposure by closing the iris slightly, and the exposure on your subject is compromised. It looks like a cloud has passed in front of the sun, when all that has happened is that the camera has changed the exposure.

Manual exposure is always a better choice if your camera offers it. Setting exposure properly should be done with an exposure meter. Setting exposure can be highly subjective, as videographers regularly overexpose or underexpose for dramatic effect. The procedure for setting exposure manually depends on your camera, the shutter speed, whether you're using filters or not, and a number of other things. You should, however, be able to set your exposure manually by "feel."

Look at your subject, particularly flesh tones if you're filming a person. Do they look right? Try opening your iris to increase your exposure, or closing it a bit to reduce the exposure. Look critically, and make sure you have what you need. If you're unsure, it's better to underexpose than overexpose. You can always add a bit of brightness during editing.

Easy on the pans, tilts, and zooming
Similarly, you should try to avoid panning (moving the camera from side to side), tilting (tilting the camera up or down), and zooming in on or out from your subject. First, these camera techniques are used sparingly by the pros, so if you use them too often or inappropriately, they're a dead giveaway that an amateur is behind the camera. Second, they place lots of motion in the video frame and consequently degrade the quality of your final product.

Compression: A step-by-step example

Now that you know a little bit about how compression works, it's time to play around with it to see how it affects the sound of your podcast. For this example, we'll be using the compressor that comes with Audacity.

1. Open Audacity, and open your podcast file.

2. Select the entire file by pressing Ctrl-A (Opt-A on a Mac). Remember that Audacity doesn't expose the effects until you highlight a section of your audio.

3. Select Compressor from the Effect menu. This brings up the Dynamic Range Compressor window, as shown in Figure 1.


Figure 1: The Dynamic Range Compressor in Audacity

4. You can see in Figure 1 that the default settings for the Audacity Compressor is a 2:1 compression ratio, a -12dB threshold, and a .2 second attack time. (This plug-in doesn't have a release time setting.) In fact, this is a nice moderate setting that may work just fine for your content. However, you may want to experiment with the settings to see what changing the threshold, ratio, and attack times do to the sound of your file.

Audacity's Dynamic Range Compressor settings are adjustable in increments. For example, the ratios are variable in .5 increments (1.5:1, 2:1, 2.5:1, and so forth), and the attack times in tenths of seconds. Try changing the compression settings to a 4:1 ratio and a .1 second attack time. Preview the audio. Hear a difference?

In fact, 100 milliseconds is really too slow of an attack time. To hear why, try changing the threshold to something really low, say -30dB. Preview the audio. Hear that? The audio starts off loud, and 100 milliseconds later the compressor kicks in. The compression effect is audible, because the attack time is too slow. However, if you raise the threshold up to say -15dB, the effect may not be as audible. You should be able to find a threshold that works in conjunction with the sluggish attack time.

EQ: A step-by-step example

This section steps you through the EQ process, with both graphic and parametric EQ. We'll assume that this is a male voice track that needs a little bit of sparkle. We're trying to do the following:

- Add a bit of warmth to the bottom end.

- Add a little clarity to the midrange.

- Give the vocal a bit of air, a little extra shimmer.

We're going to assume that you're using a software equalizer, though there's no reason that this couldn't be done using a hardware EQ. Also, the frequencies we're choosing in this example may not be the best frequencies for your audio, although they're probably a good place to start. Remember: Use your ears:

1. First, roll off the extreme low end. Chances are good (unless you have an extremely deep voice) that there is no information down here, except for possibly some room noise. Let's roll off everything below 60Hz.

On a graphic EQ, push down the faders below 60Hz. If you have more than one, start off gradually, rolling off about 3dB at 60Hz and then increasing the roll-off with each lower frequency.

On a parametric EQ, choose a high-pass filter at 60Hz and roll it all off. Shelving EQ has gradual roll-off built in.

2. Listen to your audio. You shouldn't hear much of a difference, if any. That's fine. You may hear a slight clearing up of the sound, and if so, that's even better.

3. Next, work on the midrange, because it's the most important. To give a voiceover a slight lift, you can boost the upper mids in the 2 – 4KHz range.

On a graphic EQ, pick a frequency in this range and boost it significantly, say 6-10dB. Preview your audio. Return that frequency to no gain, and try boosting the frequencies on either side, previewing each time. When you find the frequency that sounds best for your content, boost it 3dB and then boost the frequencies on either side 1.5dB, so there's a nice gentle lift. Preview the audio, and make sure it sounds good.

On a parametric EQ, choose a narrow Q and boost a frequency in the 2 – 4KHz range. Preview your audio. Try moving the frequency setting up and down, until you find the right frequency. Preview the audio each time you change the frequency. After you settle on a frequency, widen your Q to approximately 1.5. Boost 3dB, and give your audio one last preview to make sure you're doing the right thing.

4. Now listen to the low mids. The low mids are roughly where the sounds "er" and "uh" live. (If you've ever seen a sound check before a live gig, you'll hear the audio engineer making these sounds in the mics to check the EQ.) These frequencies give our ears information about the size of a room. You can often clear up a mix by cutting here, but be careful: You can make your audio sound too thin if you cut too much.

On a graphic EQ, you can experiment with cutting around 300Hz. You can do the same on a parametric EQ, with the added benefit that you can make the Q very narrow, to avoid thinning out your mix too much. Be sure to preview your audio to make sure you're making it sound better and not too thin.

5. If you're worried about the bottom end of your audio, particularly after cutting a little at 300Hz, you can add some warmth by boosting the bottom end. We rolled off the extreme low end earlier, but those frequencies are generally inaudible on most systems. To add audible bottom end, you need to boost in the 80 – 200Hz region. Where you boost depends on what (or who) you're EQing. The bottom end of male voices is usually around 100Hz; female voices are closer to 200Hz.

On a graphic EQ, you can find and push the frequency you're looking for. You may want to push the frequencies on either side slightly, as well. And the same goes for parametric; find the frequency, choose a fairly wide Q, and boost a bit. Preview your audio.

6. Finally, you need to decide if your audio needs any final sparkle. You can add this by boosting your high frequencies ever so slightly.

On a graphic EQ, start lifting at around 5KHz and boost the frequencies above 3dB. On a parametric EQ, select 5KHz for your shelving frequency and boost 3dB. Preview your audio. If you're happy with the sound, apply it! You may want to save this as a preset if this is a setting you think you'll be able to reuse.

Figures 1a and 1b show the results of all the preceding steps using graphic and parametric EQ. Your results may be slightly different; in fact, they should be, because you're listening to something different!




Figure 1: The results of the step-by-step example, illustrated on a) a graphic EQ and b) a parametric EQ.

Setting up a gain structure: A step-by-step example

It's time to set up your gain structure to produce high quality audio. The procedure is simple, starting with the first piece of audio equipment and working your way through the signal chain until you get to the final destination, your computer.

For the purposes of this example, we'll assume that you're using a microphone and a mixing desk, a USB audio interface, and recording straight to your hard drive. Your audio setup may differ slightly, but you should be able to follow these steps regardless:

1. Connect your microphone to your mixing desk, your mixing desk to your USB interface, and your USB interface to your computer. You should be using balanced cables whenever possible, because they provide a solid connection point and are highly noise-resistant. Turn on your mixing desk. If you're using a condenser microphone, be sure to turn phantom power on (or you won't hear a thing).

Tip : Be sure to turn on phantom power after you've connected all your microphones. Some microphones may be damaged if you plug them in with the phantom power already turned on.

2. Make sure you're monitoring only the microphone channel. Some mixing desks have "Solo" buttons to accomplish this; if your mixing desk doesn't have a solo button, then make sure all the other channels are turned down.

3. First, set the input level of the microphone. Do this by adjusting the input level (or trim) knob at the top of the mixing desk channel your microphone is plugged into, as shown in Figure 1. Speak into your microphone, and adjust the input level. The Mackie Onyx 1220 uses a peak meter, so adjust until it is peaking at -6dB to -3dB. A few peaks over zero are okay.


Figure 1: Setting the input level on a Mackie Onyx 1220 mixing desk Courtesy Mackie Designs, Ltd.

4. To set the output level of the mixing desk, take the channel out of solo mode if your desk has a solo button. The meters on the mixing desk will now show the level of all channels combined. Turn your microphone channel up to 0dB (on some desks this is marked "U" for unity gain).

5. Mixing desks allow you to move things from side to side in the mix. This is known as panning, and is controlled by the pan knob on your mixer. Each channel has a separate pan control. Make sure your microphone is in the center of your mix. Check the pan setting to make sure it's right in the middle. Sometimes conversations between two people can sound more intimate if the two speakers are panned slightly to the left and right, but most of the time — and especially when setting up your gain structure — all microphones should be right in the middle of your mix.

Tip When recording an interview between two people, it's tempting to pan one person hard left and the other hard right. That may sound cool at first, but it isn't. It ends up sounding like ping-pong, where the voices are jumping from one speaker to the other. If your listeners are using headphones, you'll drive them absolutely crazy. A little separation is fine, but don't go overboard. And remember that if you're using stereo for separation, you're going to have to encode in stereo, which requires a higher bit rate to sound good.

6. Adjust the final output of your mixing desk by adjusting the master volume. This is generally on the lower left of the mixing desk, below the meters. You should set the output meters to -6dB to -3dB, leaving a bit of headroom for the unexpected.

7. Next it's time to move on to the USB audio interface. Depending on the make and model, you'll have some sort of meters and some sort of input adjustment. On some models, the metering can be fairly rudimentary. Adjust to keep your level consistent with the output level of the mixing desk. If you don't have full meters on your USB interface, you can use your recording software to check your input level. Open your audio editing software. You may need to put it in record mode to get to the level meters. Make sure your level is in the -10dB to -6dB range, and remember that anything over zero will distort!

Note Some USB audio interfaces come with special software to adjust the input level. If so, use this software to set your levels. After you've set the level via the software application, the level is automatically set for your audio editing software.

Congratulations. You've just set up your gain structure. Each piece of equipment is operating in its optimal range, so you should be producing a high-quality, noise-free audio signal. The best part about setting up a gain structure is that after you've set it, you shouldn't have to worry about it anymore. You can make small adjustments if necessary using the channel adjustments or the master volume output of your mixing desk.

Tip If you're connecting a number of different audio sources to your mixing desk, label the channels so you know what is coming in on the channels. Some mixing desks have an area to do this, known as a channel strip. If your desk doesn't have a channel strip, you can always create one by stretching a strip of masking tape below the channel faders (or knobs). Then you can write on the masking tape. Believe me, when you're grabbing for a fader in the middle of a podcast recording, knowing which fader is the right one is critical.

If you have more microphones or more equipment that you want to use during your podcast, you should set the input level for each channel just as we did for the microphone channel in the previous example. You can adjust the relative volume for each channel as needed using the channel level adjustments, so that all your inputs are mixed together at the right levels. Now that your levels have been set, you need to learn a little about digital audio.

Caution Make sure you always plug microphones into mic inputs and line level equipment such as CD players and iPod headphone outputs into line level inputs. Most inputs are clearly labeled as one or the other or have a switch that determines the expected input level. If you plug a microphone into a line level input, you won't get enough gain. Conversely, a line level output distorts a microphone input. Just because a cable fits doesn't mean it's the right input!

Understanding digital audio
At some point, your audio is going to have to be digitized on the way to becoming a podcast. Digitizing is the process of converting an analog audio input into a digital audio file. Whether you're recording directly to your hard drive or you're using a digital recording device, you have to choose which digitization settings to use.

To fully understand what is involved in digitization, understanding how digital audio files are created is important. Figure 6.3 illustrates an audio signal. The audio signal starts off as a continuously changing voltage. This voltage is created by the vibrations of the diaphragm inside a microphone and is what eventually causes the cones inside a speaker to vibrate and reproduce the original sound.


Figure 2: A sound wave and how it is digitized using samples

To store this as a digital audio file, we take measurements of the wave at specific intervals. These measurements are known as samples. In Figure 2, each section of the wave has different numbers of samples under it. The number and accuracy of these samples determine how accurate the digital version of our audio file is and therefore the fidelity of the digital version to the original.