Operator`s manual

Model VR240 Audio Logging Recorder
3-4
January 2000
a. After pressing the
Config
and
System
soft keys, press the
Sampling
soft key.
b. Press the
Change
soft key to cycle through the available sampling rates.
16 KBPS
(kilobits/second) is the slowest sampling rate available, and gives the full
recording time available from a DDS media or magneto-optical disk. Normal voice
signals are perfectly intelligible at this rate, but the signal sounds somewhat more harsh
and noisy than the faster rates. This should be used when the media is to be played
back only for human listeners.
32 KBPS
is an intermediate rate that is generally satisfactory for recording all but
facsimile and the highest speed modem transmissions.
64 KBPS
should be used only for recording high-speed modem or facsimile
transmissions. There is little or no audible difference between the 32 and 64 KBPS
rates, and for broadcast logging, 64 KBPS simply uses media faster with no real benefit.
64K is not available in VR240s with more than 16 channels.
c. Press the
Done
soft key to save your setting and return to the system configuration
menu.
A technical note: Normally one would expect sampling rate to change frequency response. The
VR240 has a fixed frequency response of slightly over 3 kHz. This would normally imply a
sampling rate of about 8kHz and, in an 8-bit system like this one, a 64K (8 times 8) bit per
second sampling rate would be required. Since that is the highest sampling rate used, you can
see that something is being done to lower it. The DSP algorithms used at 32K and 16K, in
effect, discard redundant information, and enable the full bandwidth to be reproduced with fewer
bits per sample than would otherwise be required. The DSP algorithm is almost “lossless” at 32
KBPS, but does cause some degradation at 16 KBPS.
SYSTEM CONFIGURATION:
<
Sampling
Security MediaUsage Quit >
TRANSCODING RATE: 32 kbps
Change
Done