Blaupunkt Understanding the Benefits of HUSHm Noise Reduction in Audio Systems

HUSHm NOISE REDUCTION AND DOWNWARD EXPANSION GATING

High quality compact discs provide very wide range volume levels with low background hiss levels. Unfortunately, the car is a very noisy electrical environment so vehicle noises (pops and alternator whine) often creep into the audio signal somewhere in the installation. Although mid and high level music tends to mask background noises, vehicle noises become quite audible, and annoying, during quiet music passages. This problem has been known for some time in the professional audio field so a device known as a “Noise Gate” has been used to mute the signal path during quiet passages. The problem with this system is the “choppy” sound as the Gate opens and closes with music which is known as “pumping”.

The HUSHTM noise reduction circuits avoid this “pumping” by the use of a downward expander which effectively expands the dynamic range of the signal thus pushing down the background noise in relation to the desired signal. Also, the HUSHTM circuits offer a continuously variable set point that smoothly moves up and down so none of the dramatic “pumping” of the desired signal is experienced as with a noise gate. An added benefit is the ability of the HUSHTM circuit to reject noise on recorded music such as cd’s, cassettes, and even on the AM/FM car radio.

INPUT/OUTPUT ELECTRICAL TRANSFER FUNCTION

- 80 -60 -40 -20 OdB

OUTPUT SIGNAL OUTPUT SIGNAL OUTPUT SIGNAL

SIGNAL TO NOISE CHARACTERISTICS

VERY LOW

MUSIC SIGNAL

LOW LEVEL

MUSIC SIGNAL

MID LEML

MUSIC SIGNAL

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