Lectrosonics UR190 Manual do Utilizador descarregar pdf (Página 4)

The Dual Band Compandor is driven by a multiple pole active low-pass filter. The filter ensures that

supersonic noise will not cause the compandor to increase gain incorrectly. This filter also drives the

-20dB and 0dB modulation LEDs.

Traditionally, compandors have been a source of distortion in wireless microphone systems. The basic

problem with conventional systems is that the attack and decay times are always a compromise. If the

time constants are fast, high frequency transients will not be distorted, but this will cause low frequency

distortion. If the time constants are slower, low frequency audio distortion will be low, but high

frequency transients will then be distorted. The 190 system introduces an entirely new approach to

solving this basic problem, called "dual-band companding."

There are actually two separate compandors in the 195 system, one for high frequencies and one for

low frequencies. A crossover network separates the frequency bands at 1kHz with a 6dB per octave

slope, followed by separate high and low frequency compandors. The attack and release times in the

high frequency compandor are fast enough to keep high frequency transient distortion at a low level,

and the low frequency compandor uses slower time constants, reducing low frequency distortion to well

below that of a conventional compandor.

The compandor senses the signal level, and dynamically increases the gain for loud signals or

decreases the gain for soft signals. In this way, the original dynamic range of the transmitted signal is

restored, while preserving a high signal-to-noise ratio. The expansion ratio is 2:1, which produces a

2dB change in output signal level for a 1dB change in input level.

The balanced microphone level output circuit generates a truly balanced signal at the XLR output

connector. The volume control is a balanced attenuator, and gives a gain range from -20dBV (at full

modulation) in the fully clockwise position to -50dBV in the fully counter-clockwise position. In addition,

the headphone circuit is driven from the microphone circuit. This means that the headphone output

level is dependent not only on the headphone volume control, but also the microphone level control.

1 2 3 4 5 6 7 8 9 ... 12 13

Sem comentários

Lectrosonics UR190 Manual do Utilizador Página 4