Signal Properties Filter Block

General description

This block provides a set of general settings to be used to modify incoming signal. DC offset and gain can be set to certain level. The automatic gain control can be activated. DC offset can be automatically detected and removed. The saturation for D/A converters can be set active. The noise squelch can be activated.

 

 

Parameters

DC offset

This is the DC offset (average) by the user. The scale in the 8 bit mode is –128…127 and in the 16 bit mode –32768…32767.

 

Automatic DC removal

The properties filter can remove the DC offset automatically. This ensures that the average of signal is zero.

 

Gain

The signal power can be changed to give some gain into the Gain field. The gain can be positive or negative. The negative gain means attenuation. Gain values are given as decibels i.e. 6 dB gain doubles the amplitude of output signal.

 

Automatic gain control

The switch activates the AGC. The maximum amplitude in the output is given by the optimum level parameter. So, for example, if the optimum level value is –3 dB the maximum output values are 3 dB below the maximum amplitude, which can be presented in 8 or 16 bits.

 

Optimum level

This is the optimum level value for the AGC. The optimal level shows how many decibels the output power is below the maximum power of the output device. The maximum output power depends on the output device format i.e. 8 or 16 bits per sample.

 

Average time

This is the time used to estimate the signal levels for the AGC. If this time is too short, the output level might change too rapidly. If the time is too long, it may cause signal overflows.

 

Saturation mode

The switch to activate the saturation mode. The saturation prevents big signal changes in sound card’s D/A converters. If saturation mode is active all signal samples, which are over MAX_VAL are set to MAX_VAL or less than MIN_VAL are set to MIN_VAL. In 8-bit mode MAX_VAL is 127 and MIN_VAL –128. In 16-bit mode MAX_VAL is 32768 and MIN_VAL is –32767.

 

Squelch

The switch activates the noise squelch. If the noise squelch is activated and the pure white noise is detected, the set output is set to quite state. When some signal (not just noise) is again detected the squelch will connect the signal again to the output.