The 911 incorporates one channel
of encode and one channel of decode circuitry
in the dbx® Type I format. The Type I system
doubles (up to a maximum of 115 dB) the dynamic
range of the storage or transmission medium.
This is achieved through compressing the signal
by a 2:1 ratio during record then expanding
the signal 1:2 with a precisely complementary
deemphasis during playback. The companding is
linear over a 100 dB range. It requires no pilot
tones or special calibration.
Type I provides best results when
used with transmission or storage media exhibiting
flat frequency response (±1 dB 20 Hz
- 20 kHz) - typically open reel recorders running
at 15 or 30 ips, or digital media. The signal's
dynamic range is cut in half, with the hottest
levels considerably reduced and the softest
passages boosted. On decoding, the signal is
precisely expanded back, and the original dynamic
range of the program is retrieved without hiss,
saturation distortion, or degradation of frequency
response.