Peak Limiting - Rane C4 Operator's Manual

Quad compressor / limiter

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Operator's manual (12 pages)

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Figure 2. The C4's De-essing performance remains consistent with

varying input levels

This is all nice and technical, and repeating it word for word

will undoubtedly impress friends and family, but what does it

really mean? Simple: de-essing performance is consistent and

predictable, regardless of how loud or quiet the singer/talker is.

Taming sibilance when the talker is quiet is just as important as

when the talker is at a fevered pitch. Only a true de-esser oﬀers

this performance.

Figure 3 shows what happens when a compressor (not a true

de-esser) is used in conjunction with a side-chain EQ. Sibilance

during loud passages is attenuated, but there is little or no gain

reduction during quiet passages, even though there may still

be a signiﬁcant amount of "sss" in a person's voice. For a given

threshold this often results in an overly-aggressive eﬀect during

the loud choruses, and a completely ineﬀective result during the

hissy, whispered verses. Solution: use the C4's dedicated De-ess

mode instead.

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Figure 3. A compressor with a simple side-chain EQ boost is not a true

de-esser. Gain reduction is directly aﬀected by varying input levels,

not the actual ratio of broadband to sibilant material.

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Peak Limiting

A limiter is just a compressor with a really high ratio, right?

Well...not exactly. Although the two devices use similar termi-

nology (Threshold, Attack, Release, and so on), they serve two

completely diﬀerent purposes and therefore operate in diﬀerent

manners. Fundamentally, a compressor uses an rms detector to

keep the average level of a signal under control, while a limiter

uses a peak detector to act on the instantaneous level of the

signal.

Primary uses of limiters: 1) preventing clipping and distor-

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tion in power ampliﬁers, 2) protection of loudspeakers from

damage resulting from destructive transients [like the proverbial

dropped microphone] 3) preventing overs [clipping] during

digital recording 4) preventing overmodulation of the transmit-

ted signal in broadcast.

Figure 4 shows the eﬀect of limiting a signal. The top line is

the original, full volume input signal we need to limit – perhaps

the unfortunate blast of noise when the vocalist inadvertently

unplugs the phantom-powered mic. The bottom line shows the

limited output. At no point does the output signal ever exceed

the threshold, demonstrating the limiter's brick wall capability.

Contrast this with Figure 5, which shows a compressor set to a

high ratio (∞:1), and a fast attack time. Due to the compressor's

averaging eﬀect, the output easily overshoots the threshold, and

transient peaks are missed altogether. And it's these peaks which

can potentially ruin your speakers or the perfect recording take,

and possibly your reputation.

Input

Limit Threshold

Output

Figure 4 Limiter performance showing brick wall characteristic.

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Input

Limit Threshold

Output

Figure 5 Compressor used as a limiter. Signal peaks can still exceed

threshold, even at high ratio settings.

Overshoot

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Peak Limiting - Rane C4 Operator's Manual

Peak Limiting

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