Tips for Recording Good Audio
Recording high-quality audio for the Web is generally no different than recording high-quality audio for film, TV, radio, music CDs, or any other format. But there are a few tips to keep in mind when recording audio exclusively for the Web.
Select the Highest Sample Rate Possible
Even consumer-level digital video cameras can record audio at CD-quality levels. Some cameras allow you to select the number of times per second the voltage in the microphone signal is sampled, known as the sample rate. The higher the sample rate of a sound file, the smoother that sound's playback quality. These cameras also allow you to select the sample depth, which dictates how many bits the computer will use to describe each sample it takes. Be sure to record at the highest sample rate and sample depth possible. The bigger and the more frequent the samples you feed to the compression software, the better your Web movies will sound.
If you're recording to an analog video camera or to an analog tape deck, you'll have to rely on the hardware capture card that you'll be using to digitize your audio track (more on this in Chapter 4, "Capturing Capably"). While you'll end up with a digital audio file to edit this way, you'll get better Web audio files if you record digitally from the start (either with a camcorder or with a digital audio recorder), because digital audio files have better dynamic range and less noise.
Keep the Sound Simple
While computers are capable of CD-quality audio, people still sometimes attach cheap loudspeakers to their computers, and their computers are often located in noisy rooms. If your Web movie has an elaborate, multilayered sound track (with several layers of dialogue, music, and narration), people may well miss most of it.
Unless it's isolated on a very specific frequency, it's difficult to remove noise from a sound track that has dialogue. That's why it's a good idea to record the cleanest audio possible while you're shooting.
Getting Audio Without a Microphone
As with video footage, there is a way is to get audio from somebody else instead of creating it yourself. Stock music and sound effects libraries offer sound tracks that you can use.
So that you have some files to work with, I have included stock music and stock sound effects on the CD-ROM that comes with this book.
Get That Microphone Closer!
Get the microphone as close as possible to the person or thing you're recording. Ideally, you would have an experienced boom operator who would hold a shotgun microphone at the sound source, just above or just below the edge of the camera frame. The second choice would be a good-quality, body-mounted lavaliere microphone with a short pickup radius (which would reject unwanted sounds off in the distance). Unfortunately, lavaliere microphones usually pick up more noise than directional microphones.
Keep It Quiet
Your goal when recording audio is to reduce noise, both ambient noise and electronic noise. Ambient noise is all the unwanted sound that occurs on the location or set where you're shooting. Electronic noise is generated either in your recording device or in any equipment connected to it through a cable.
Audio compression software doesn't know the difference between unwanted noise and the sounds you actually want to include in your Web movie. If you give the compression software a noisy signal, it will waste precious bits of the data rate on the noise. Here's a better idea: Record the cleanest (noise-free) audio possible.
When working in an uncontrolled location with a lot of ambient noise, you can do things to minimize the noise:
Put sound blankets (furniture pads or any sound-absorbing material) on walls and floors to deaden echoes.
Put sound blankets on windows to minimize traffic noise from the street.
Turn off the air conditioner or any other noisy appliance.
Avoid rooms with reflective, noisy surfaces (like stone tile floors). Find a room with wall-to-wall carpeting instead.
Wait for that plane or bus to pass by before rolling.
If you're shooting outside, make sure to use a wind screena foam sock that you pull over the microphone so that it doesn't record wind noise.
If at all possible, record voice-over narration (narration that's not on camera) in a studio, after the shoot is over. This gives you much more control over the sound environment.
Turn off the automatic volume control on your camera. Most cameras have a fully automatic mode (designated with the capital letter A) and a manual mode (designated with the capital letter M). Manually adjust the levels while listening to your sound source with headphones. Good headphones will seal your ears so you hear only what is actually being recorded. Good video cameras will have volume unit (VU) meters that indicate the volume level of the signal (either with a needle or an LED readout) while it is being recorded to tape. This gives you some visual feedback while you're adjusting the volume level as the sound source loudness is changing. Put simply, you want to adjust the volume level so that there is activity in the middle of the meter, with only infrequent movement into "the red"or the upperportion of the meter. Too little movement in the meter will result in a low, noisy recording; too much movement into the red will result in distorted sound and, in the case of digital cameras and recorders, digital noise. If you are not sure about the meter levels, then just use your headphones as your guide.
Reduce Electronic Hum and Noise
The low-voltage signal in an unbalanced microphone cable can easily pick up noise and hum from nearby electronic devices. Keep audio cables away from power cables, or at least cross them at right angles. This minimizes the amount of contact between the cables. You also might get a hum if your camera is plugged into the same power circuit as other audio and video equipment. If this is the case, try a different outlet or use batteries. If the camera is connected electronically to anything plugged into an electrical outlet, disconnect it.
Using Separate Microphones for Separate Tracks
High-end cameras (the ones costing over $4000) have more than one audio input and will record audio separately, on different tracks on the tape. This means that you can plant multiple microphones in different parts of the shot (for example, one microphone per person, in a panel discussion). Then you can mix (adjust the relative levels) of various tracks later when you're editing. On professional shoots, use at least two microphones if possible: one lavaliere and one handheld directional microphone. This allows for more options later in editing to mix in just the right amount of room tone.
Before you leave a particular location or camera setup, it's always a good idea to record the sound of the room. This will often be useful later in editing, to smooth over transitions and scene changes in your program. Ask the crew or anyone else present to just be quiet for a moment while you record the sound of the seemingly "silent" space.
Sidebar: What Sound Looks Like
You will often hear the words "frequency" and "pitch" used interchangeably. For the purposes of this book, we will make the following distinction: "frequency" is the physical measurement; "pitch" is how high or low the vibration sounds to our ears. Besides the speed (frequency) of the vibration, the other defining feature of a sound is how strong the vibration is. The stronger the vibration, the louder it sounds to us. Physicists and sound geeks use the term "amplitude" to describe this. So, just for the record, amplitude is the physical measurement of the strength of the vibration. (And "loudness" or "volume" is how the strength of the vibration is perceived by us humans.) Over time, waveforms create complex patterns. You will see these complex shapes when you edit sound tracks in Premiere. Figure 3.13, for example, from Premiere, shows a recording of a human voice. If you look closely, you can also see individual waves.
Figure 3.13 This snapshot from Premiere shows a recording of human voice as it looks in waveform.