Marc Marc

Dynamic Noise Limiter
Custom designed for Sluik/Kurperhoek

Features - In general - DNL function - GATE function - Alternating setup

photo front panel


Block Diagram

____ DNL features:

  • 2 Channel DNL & Gate
    • Used as 2 mono or 1 stereo channel
    • Noise limit Cutoff frequency control
    • Noise limit depth controls (ENV)
    • Noise limit Time Response controls (ENV)
    • Function select DNL / GATE (ENV)
    • Function select N / Join (ENV)
    • LED indication (ENV)
  • Power Supply



In general

This DNL device can be used very well to suppress Noise in the silent or low volume parts of Music or Voice. Any LINE input signal can be applied to be treated - to lower down the Noise in the critical low volume parts of a signal. From Psycho-Acoustic research it is know that the higher frequency spectrum may de damped in the low volume parts without harming the impression of the listener. Because most of the annoying background Noise lays in this higher frequency spectrum and becomes significant in the low volume parts or the 'silent' parts, it is very effective to have the higher frequency spectrum suppresses at these moments.

When this DNL is used as a GATE, then the dynamically suppression concerns the whole frequency spectrum and thus acts as a automatic volume control which responds to the input level. This is very useful for VOICE and after a signal has passed a Hard Distortioner (guitar). It shuts down or lower downs the volume at the silent parts and lets you regulate the characteristics for this. At a certain Gain setting, it also will act as a kind of expander (low parts become lower and loud parts become louder).

This Dynamic Noise Limiter & Gate is build around a so called LDR & LED combination. An 'obsolete' technology to create a Voltage Controlled variable resistant to function in a High Cut filter configuration. You find this technology in early Synthesizer design (in the VCA's) and the electronic Organs (volume pedal).
You may wonder why this technology was used to design the DNL device. Well, there is a great advantage with this technology. In contrast to later technology, the LINE input signal does not have to decreased to go through the electronic circuit and thus also does not need to be amplified again to bring it back on LINE level at the output. Secondly the harmonic distortion at high input levels increase naturally. This in contrast to the more absolute limits of newer technology which starts to distort the signal more suddenly when the limit is exceeded. Thus the signal input headroom is with this 'obsolete' technology larger.
Because the input Signal is not weakened and later amplified again the Signal to Noise ratio (S/N) of this DNL device does not degrade.
This DNL system is strictly taken slower (response) than its modern counterparts. But, in practice it is sufficient and turn out to respond very naturally due to the characteristics of the combination LDR (Light Depending Resistor) & LED (Light Emitting Diode) in the designed configuration.
Conclusion: Although this DNL is designed with 'obsolete' technology, the results and specifications still can compete with modern technology and has its own valuable characteristically response.


DNL function

It works very simple: When there is no signal detected then the Noise suppression is at maximum and all the background Noise is suppressed (depending on the CUT controller). The higher the volume level of the signal, the less suppression of the High Frequencies (less High CUT). The response characteristics can be adjusted with the Gain and Time control. A high Gain lets the DNL faster fade into a non-suppression mode and thus only at the completely silent parts the noise will be suppressed. A low Gain will do the opposite. It then will let the DNL faster fade into Noise suppression when the volume goes down. With the Gain control you can set the response anywhere between these two extremes.

To prevent that the DNL is following the input volume dynamics so fast that the suppression becomes a clearly to be heard effect and thus unwanted, you can set with the TIME control the response speed. This lets you respond the suppression to a more or less all-over characteristic. For Spoken Voice for example, you would set the TIME control at fast and for a total piece of music with many volume dynamics mixed on background instrumentals, you would tune the TIME to be respond slower.

With the N/JOIN switch you can have both channels either responds completely independently (N = Normal) or combine the two detection control signals into a Joined mode to have the same effect on both channels. This means that both channels in a stereo signal setup respond more natural.


Gate function

When the DNL/GATE switch is set to GATE, you will let the DNL suppress the whole frequency spectrum. It is a slight modification of the electronic circuit of the DNL but, it might have rigorous effect. When used slightly, it works as a smooth expander with the result that full silently parts drop to fully to zero and thus not any Noise or whatever background signal errors come trough. Depending on the setting of the GAIN, TIME and CUT controls the output volume curve follows the input volume curve with certain characteristics.
The GATE function works perfect for input signals which include irritating background Noise and/or sounds in the 'meant to be silent' moments. For example: Spoken VOICE in a situation with far distance background sounds or for example a guitar connected to a Hard Rock Distortioner which even when you do not touch a string already give a strong background sound due to the extreme amplification of the Distortioner. You also may have noticed whenever you have used a Hard Distortion device that at the end of a long sounding string or chord, the Distortioner cuts off the sound and then let it return again. This happens several times due to the way that a guitar string fades away its vibration curve. The GATE function of the DNL lets you set with the GAIN and the CUT control a response that shuts down the guitar string sound after its first drop out and thus the couple of after volume sweeps do not come through anymore).

In particular with Staccato played sounds (or instruments as Drums) the GATE function with its possible controls let you introduce certain effects related to your way of playing at the instrument.


Alternating Setup


You very well may patch both channel in a cascading setup (2 stages in series). Thus The output of the first stage is connected to the input of the second stage and the output of this second stage is the final output. This doubles the effect and/or combines the differently set effects of each stage.
You could, for example, have both stages set to a slow responding Noise suppression. The result could be (depending on the GAIN and CUT settings) that the Noise suppression curve becomes logarithmically. It also can be set to act on two different cutoff frequencies. The first stage only suppresses smoothly and the second stage only cuts the full silent parts to get rid of the background noise.


You also could feed both channels with the same input signal and connect both outputs to your mixer to have both signal joined again. By setting a different Noise suppression or GATE curve, you can mix both these effect to be combined in a single more complex suppression / gate effect.

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