Limiter with "Zero" attach time?

Dear Sir,

Any suggestion?

Thank you

Moving discussion to the SigmaDSP forum for follow-up.

-Joe

Hello,

One way to achieve a fast limiter is through a feed-forward approach. This works by measuring the incoming peaks to instantly calculate (instead of settling upon via feedback) the required gain reduction. An example is shown below:

The absolute value and AB blocks select the higher peak level of the two channels to insure that neither goes over the limit. The clipper forces a normal gain of 1 when below threshold. Then the peak envelope block measures this peak level. Feedback around the external-decay version of this block provides an exponential (constant dB rate) decay -- this technique is described at Workaround: Creating constant-dB envelope decay using an existing linear decay algorithm

The reciprocal of the resulting level value is applied to slew volume controls to limit the audio level. A short look-ahead delay is shown, but it may not be needed.

With a rising musical input, we see the gain (top graph) dive below 1.0 as needed to keep the level (bottom graph) below 1.0 peak at all times. Unlike limiters that close a feedback loop around the output volume, this one doesn't overshoot its correction. Thus it doesn't sound as bad on music as most others. I tried two other designs that bombed terribly before this one -- it wasn't easy.

Best regards,

Bob

Hi @KJBob,

I have the exactly the same problem but on the 1452. I have tried this algorithm, but have difficulty on the holding time tuning as I have used the same values as the one above. Can you give a working sample for the 1452 version?

Thanks is advance!

Dan

Hello Daniel,

Try the attached project, making adjustments as needed for your application:

Limiter Recovery Rate -- the rate at which gain returns to normal after a loud sound is gone

Control Attack-Decay at the Slew Volume -- set it very fast to get the desired "zero attack time" --

for setting time constants, see https://ez.analog.com/message/165526#165526

Look-Ahead -- Increase to eliminate any overshoot on sudden inputs. SigmaStudio seems to have trouble saving this setting with the project.

Headphone Volume -- This is just to reduce headphone level for my tests.

Limiter Level Adj -- Increasing this gain beyond unity reduces the level at which the limiter cuts in.

Best regards,

Bob

Dear Bob,

A million thanks to you!

Dan