|
|
10 tips for nonlinear sound
More tips
By Loren Alldrin
1. Mind your rates and bits
Most computers give you several sound quality options for
digitizing your audio, specifically in the areas of sample rate and bit depth.
Though you can change an audio file's parameters after digitizing, it's best to
pick one setting and stick with it for a whole project. Also, keep in mind that
better quality audio translates into more disk space used.
Sample rate controls the frequency response of the audio
file, while bit depth controls its "resolution." A sample rate of 32kHz (kiloHertz
or "thousand Hertz") is great for consumer video; rates of 44.1kHz (CD quality)
and 48kHz may be overkill. A 22kHz rate, though borderline, still sounds good
and preserves disk space.
Audio digitized at 16 bits is optimum for video. Using 24
bits per sample is overkill, and 8-bit audio can sound "gritty" and coarse. For
sound effects and other low-fidelity sounds, however, the added edge of 8-bit
audio can be a plus.
2. Digitize strong, but not too
strong
As with any recording medium, nonlinear systems do best with
a strong signal. Digitize your audio at as high a level as possible without
sparking the "clip" indicators (usually red) on your meter. Though you can
normalize a sound after-the-fact to increase its level, getting a strong signal
to begin with is always best.
Some editing systems have over-active peak indicators,
meaning a brief flash of red isn't the end of the world. Zoom in on the waveform
itself to see if the top or bottom of the peak is really clipped (flattened) as
in Figure 1. If you can't see or hear any clipping distortion, you don't need to
adjust what you've already recorded.
3. Normalize
Normalizing an audio file brings its level right up to
maximum. This usually overwrites the original file, making normalization a
"destructive" process (more on this later). If you can't boost an audio file
adequately with a track fader, normalizing may be your only option.
It's important to understand that normalizing doesn't add
any audio data or fidelity; it simply boosts the level of the file. Because it
can actually have a slightly negative effect on fidelity, use normalize only
when necessary.
Some normalize functions will show how far they need to
boost the signal, a feature you can use to tell whether an audio file is
clipped. If normalize says it can't make the file any louder (or returns "0 dB"
as the boost amount), your audio file probably got clipped during digitizing.
4. Don't be destructive
Some processes in the nonlinear realm affect the audio file
only on playback. We call these "non-destructive" processes, because they don't
permanently change the audio file. Destructive processes actually alter and
re-write the audio data on the drive. If your system won't let you undo a
destructive process, be extremely careful before performing it.
It can be tricky to tell the destructive changes from the
non-destructive ones. In general, non-destructive changes are instantaneous.
Destructive changes take time to process the audio data and re-write the file.
If you are performing a destructive process, it's a good
idea to backup, copy or archive the audio file so you can restore it later if
you need to. When the permanent compression/EQ/pitch shift you applied doesn't
sound so good the next day, you'll be glad you can restore the original file to
the way it was before.
5. Crossfade
When splicing two sections of audio together, try a short
crossfade instead of a straight audio "cut." It's usually easiest to do this
with the two sounds on separate audio tracks. Drop the volume of the first track
over a short period (3-10 frames is plenty), and bring up the volume of the
second track over the same period. The result is a seamless transition that
keeps any background sounds or ambience at a constant level.
A sharp edit is often noticeable to the ear, and may cause a
loud "pop" if it occurs mid-sound. An edit that fades to silence and back up is
also hard to hide, as the background sound dies away for a moment.
6. Compress
As you've probably noticed by now, real-world sounds tend to
alternate between being too loud and too soft when recorded. Compression is a
process that reduces the difference between these loud and soft portions of your
soundtrack. Many nonlinear systems will apply compression as an audio "filter"
(an internal audio processor), usually as a destructive process.
Experiment with a threshold setting of around -12 dB,
compression ratio of about 2:1 and fast attack and release times. Lowering the
threshold or increasing the ratio compresses the sound more; moving either in
the opposite direction makes for less compression.
Compression can be tricky to actually hear, but its effects
are wonderful. Set correctly, compression will level out your soundtrack and add
impact.
7. Kill that noise
A nonlinear system allows you to get rid of unwanted noise
by manual or automatic means. A noise gate or "remove silence" filter will
listen for quiet sections and reduce their level even further. If you have
background noise purring along behind dialog, for example, a noise gate will
find those spaces between spoken sections and reduce the volume of any noise
present.
If you don't have a filter to do this automatically, you can
perform a similar operation yourself. Simply look at your audio waveform and
smoothly drop the volume of that track during silent sections. This is easiest
to do with a volume "envelope," which allows you to set volume points that the
computer will fade smoothly between. With some practice, you can seamlessly
remove those pesky noises that fill every quiet section.
8. Don't drive your drives too hard
Though some nonlinear systems will allow you to fill up an
unlimited number of audio tracks, remember that this really taxes your computer.
Your hard drive is trying to read several different audio files at once, as well
as keep a steady stream of video data flowing. Playback may stutter and skip,
especially if you're using a computer with a modest memory.
Submixing your audio tracks lets the computer combine all
the audio tracks into one (or two if stereo). This lessens its workload
considerably, and may insure smooth playback when a video gets complex. If you
do submix, remember to keep the individual audio files in case you need to make
changes later. Also, keep in mind that...
9. Tracks add up
If you combine a stack of nice, fat audio files, their
levels may add up to distortion. If you hear a harsh, buzzy edge (or loud
popping) on playback or after submixing, you need to reduce the level of your
tracks. Dropping every track by the same amount will keep your audio blend
intact--try just 1 dB for starters.
Some non-destructive method is preferred, such as lowering
the track faders or adjusting all volume envelopes. If your editor has a
"master" fader, you may be able to lower it a few dB to eliminate the overload.
If you must, you can drop the level of each sound with an amplify filter and
destructively re-write the audio files.
10. Catch a breath
When editing dialog or narration, breaths are nearly as
important to creating a smooth flow as the words themselves. If you perform an
edit mid-breath, the result is an awkward hiccup in the sound. If, through
editing, you eliminate breath sounds altogether, the result can be very
unnatural.
The best place to edit the speaking. We humans usually
inhale right up to the first word, then there's a brief pause as the breath
reverses and the vocal cords get going. Performing a quick crossfade (or even a
straight cut) in this gap will insure a natural flow of speech. |
|
See other tips:
|
|
|
Ads by Google |
|
|
|
Latest Updates |
|
|
|
You are not logged in.
