Cloud CX335 Посібник з монтажу та експлуатації - Сторінка 10

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CX335: Installation and Operation Manual

What is Hard-knee and Soft-knee?

The actual threshold point where compression takes place is called the 'knee', the reason

being that if a graphical representation of input level verses output level is made, then below

threshold the line will be at 45° (output is the same as input). Above threshold this line will

have a gentler slope equal to the ratio setting. So the line will have a definite 'fold' or 'knee'.

(See diagram below).

With high ratio settings this knee can be very noticeable. To prevent this sudden change

between no compression below threshold and lots of compression above threshold, it is

much gentler on the ear if this knee is 'rounded' or softened. Soft-knee is more musical and

desirable if the actual compression process is not to be too obtrusive. So by default, the

CX335 compressor limiter is a 'soft-knee' device, yet still can be overridden by use of the

hard switch.

Ratio explained.

For a hard-knee compressor, the effect of Ratio can be easily understood by remembering

that ratio is a comparison between input levels and output levels. For instance; a ratio setting

of 3:1 results in only 1dB of change at the output for every rise in input level by 3dB providing

that the input is greater than the threshold setting. A simple rule of reading Ratio settings can

be input:output, or input rise of xdB gives output rise of ydB. For a soft-knee compressor, the

Ratio control becomes a little less well defined

Soft-knee gradually changes the ratio as the signal rises above the threshold setting. On the

CX335 this change takes place for as much as 10dBs, so the selected ratio is only reached

once the signal is 10dB above the threshold setting. This changing ratio is far more musical

and disguises the fact that any manipulation of the dynamic range is taking place.

What about Attack and Release controls?

The rate at which the compressor takes effect (once the threshold is exceeded) is called

Attack, similarly the rate at which the compressor subsides (after the input signal falls below

threshold) is called Release. The wrong attack time for a compressor will have different poor

results for differing input frequencies. For instance too fast an attack time with low

frequencies will cause distortion as the gain reduction changes during one cycle. On the

contrary, too slow an attack time on high frequencies will not process the signal peaks quick

enough, resulting in the possibility of system clipping and lack of speaker protection.

The conclusion is that for broadband music programme a fixed attack time is virtually

useless. Similarly a release control that doesn't track the input programme envelope will

result in audible 'pumping' or breathing as the gain reduction changes. The CX335 gets over

this problem by constantly adjusting these two crucial 'parameters' internally depending on

15-07-02 V3

Graphical Representation of Compression and Limiting

INPUT

GRAPH OF INPUT LEVEL

IN dBs

VERSES OUTPUT LEVEL

+10

0dB

-5

-10

THRESHOLD

-15

-20

-25

-30

-25

-20

RATIO 10:1 OR LESS

-5

+10

-15

-10

0dB

NO COMPESSION

HARD KNEE

SOFT KNEE

LIMITING

RATIO 20:1 OR GREATER

OUTPUT IN dBs

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