Sample Rates and Project Presets
The sample rate of a recorded file is crucial when integrating audio from
many sources, as one does when editing video. The DV standard only
supports three sample rates: 32kHz, 44.1kHz, and 48kHz. Many DV
devices, such as Sony DVCAM devices, will only record a particular
type of audio format, at either 32kHz or 48kHz.
Resampling
Audio projects with mixed sample rates are both common and
problematic. For example, the audio track of a clip recorded on a Sony
DCR-VX1000 is digitized to the DV tape at 32kHz, and audio captured
from a CD is at 44.1kHz. When this material is assembled together, all
audio sample rates must be the same, so one clip must be converted, or
“resampled” to match the sample rate of the others.
Resampling not only adds a little extra rendering time, but can degrade
the quality of your finished audio, and can even impact the playback
performance on the computer. As such, it should be avoided if possible.
Radius EditDV will resample all audio as necessary to match the sample
rate of the project preset. In general, choosing the sample rate of your
project preset is based on the following criteria, in order of importance:
1. What sample rates are supported by my audio output device?
If you are using a Sony DVCAM device, it may refuse to record a
project with a sample rate of 44.1kHz. Panasonic DVCPro devices
require 48kHz. If your audio will be sent out to a DAT deck or an
Alesis ADAT, you cannot use 32kHz wthout resampling.
In most cases, though, DV devices will accept any of the three sup-ported
sample rates.
2. What is the sample rate of most of my audio material?
If your audio source material is predominantly 48kHz, you should
use a 48kHz project preset, so that only the odd clips are resampled.
3. What material can survive resampling the best?
If the most common sample rate in your project is on clips where the
audio is noisy, or indistinct, or intermittent, it may prove to be better
to resample those clips, and keep your more sensitive material in its
pristine state.
To avoid unnecessary render time (and to avoid problems that can occur
in project with mixed sample rates), you should resample audio clips
prior to importing them into the project.
EditDV 1.5 includes BIAS Peak LE, which is capable of resampling
audio from an EditDV project. Transferring the clip from an EditDV
project to an audio application and back is described in Application
Note EditDV Application Note #4, "Audio Import and Export".
Resampling is described in the audio application documentation.
Capturing/Resampling using a DV Device
In many cases, it may prove to be much simpler to record your source
audio onto DV tape via the audio dubbing or analog audio input
features of your device. This way, it becomes DV-compatible audio that
can be captured and batch-recaptured, and imported directly intoRadius
EditDV. In addition, the other source files can be easily archived with
the rest of the video media.
Editing with Mixed Sample Rates
If you choose not to resample the audio in an external application, or to
digitize it in the appropriate sample rate, you can still use it in EditDV.
Edit DV will resample appropriately whenever you update or overwrite
the AP track.
However, it is important not to mix audio sample rates in the same
track. If you wish to use, for example, audio captured from a CD at
44.1kHz with your 48kHz project, place the CD audio on one track and
the 48kHz DV audio on a separate track. You must update the AP track
to preview your program, but by resampling the audio at this stage you
will prevent problems when playing back from the timeline.
Audio Import and Export EditDV Application Note #4
Author: Mike Jennings
Applies to Version(s): All
Last Updated: 11/21/98
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