Back to overview Documentation version 8.50


Natural Dynamics section

Increases the dynamics for music that lacks dynamics.



Beside clipping (see Declipper), moderm music also often lacks dynamics. For an audio processor, it's much easier to work with dynamic music that has never been comprssed than to work with already compressed music - it is much harder to make such music sound good.

Natural Dynamics boosts punchy sounds in music, while attempting to avoid boosting other sounds or to boost punch in already very dynamic music.

Main panel

The main Natural Dynamics settings.

  • Natural Dynamics
    Enables Natural Dynamics.

  • Hear

  • Effect strength
    Increases or decreases the effect of Natural Dynamics.

    The Effect strength sliders of all the Natural Dynamics bands are multiplied by this value.

Bands panel

Controls the number of multiband compressor bands.

  • Bands
    Controls the content of each band.

Band coupling panel

Controls coupling between adjacent multiband bands.

To avoid very extreme effects from the multiband compressor if certain frequency ranges are nearly absent or very loud in the incoming signal, the bands can be tied together to stop a single band to move very far away from the adjacent bands.

  • Band coupling
    Coupling between all bands.

    This number defines how strongly bands are coupled if they are exactly one octave apart (Frequency doubles between bands). Bands are coupled stronger if they are closer together and weaker if the distance between them is bigger.

  • Low Freedom
    Ignore coupling for the lowest band.

    The lowest band is somewhat special: If you don't allow it to move freely, absense of bass or presence of very strong bass cannot be handled properly. On the other hand, if you want the output to stay true to the original, that's actually a good thing.

    With this slider you can determine how much of band coupling is ignored for the lowest band. Note that since bands are still coupled in both directions, the changed value of this lowest band will also have some effect on adjacent bands.

  • High Freedom
    Ignore coupling for the highest band.

    The highest band is somewhat special: If you don't allow it to move freely, absense of highs or presence of very strong highs cannot be handled properly. On the other hand, if you want the output to stay true to the original, that's actually a good thing.

    With this slider you can determine how much of band coupling is ignored for the highest band. Note that since bands are still coupled in both directions, the changed value of this lowest band will also have some effect on adjacent bands.

Flat frequency response panel

This slider helps to keep the frequency response of both sweeps and pink noise flat.

If you play a sweep through a multiband compressor, it happens frequently that the output is louder in some places than in other. Usually, it is louder around the crossover frequency between bands, although this also depends on the amount of compression.

A good value for Flat Frequency Response can only be found by trial and error, the value that gives the flattest response on sweeps should be used. It is generally also a good idea to test the response for pink noise; this slider has very little effect on pink noise but it should be flat as well, except for intentional non-flatness.

Update: With properly setup band frequencies, this slider is not needed. The default frequencies in Stereo Tool have not yet been adjusted for this. But they will be in the future, making this slider useless for most users.

  • Flat band tops
    Changes the shape of multiband processing bands.

    This enables a different band splitting mode with flatter top areas of the different bands, and a different mechanism to keep the frequency response flat.

    The advantage of this is that bands have less impact on each other, which can be used to generate a more stable sound image.

    See also Flat tops.

  • Flat frequency response
    The flatness value.

    0 does nothing, 100% moves the measurement strength at crossover frequencies from -6 dB to 0 dB. See the thin lines in the Bands display.

  • Monitor
    Plays only the output of this band.


  • Strength section

    Controls how strongly Natural Dynamics works.

    Strength panel

    Controls how strongly Natural Dynamics works for each band.

    • Effect strength
      How strongly does the filter work.

    • Dynamics Detection
      Reduces the dynamics boost for already dynamic sound.

      The effect is reduced if the signal is already very dynamic. This slider offsets the detection of how dynamic the sound already is. Result is displayed in the bars on the right (gray dotted part that comes in from the right: The bigger this is, the more dynamic ND thinks the sound is, and the effect of the filter is reduced as indicated by this gray dotted area).


    Initial boost section

    The settings for the initial required volume boost estimation.

    All the sounds that are above a certain level are increased in level. Punch filter is used afterwards to remove unwanted boosts.

    Initial detection - Boosts sounds above average level panel

    The Initial Boost settings.

    • Follow speed
      Determines how fast the average audio level is adjusted.

      Only sounds above the average level (plus a theshold) can be boosted.

    • Multiply
      Calculated level above the long-term level is multiplied by this.

      Stereo Tool calculates how loud the current sound is compared to the 'average' level. 0 = equally loud, 1 = twice as loud etc. This calculated level is multiplied by Multiply above. Basically, bigger value means more effect.

    • Subtract
      This is subtracted from the result of Multiply.

      Bigger subtract value means that the level where the filter becomes active shifts upwards (sounds must be louder for the filter to do anything).

    • Maximum boost
      Volume boost may never be more than this.


    Punch filter section

    Only boost punch sounds.

    After Initial boost, all the sounds that are louder than a specific level are boosted. But it's better to boost only sounds that are 'punchy', in other words, if the volume goes up rapidly. This filter removes boosts found in the first step if the sounds are not punchy.

    Punch filter - Removes non-punch boosts from Initial boost panel

    Boost only punch sounds.

    • Filter Punch
      Turn this filter on.

      You should actually never turn this off, except when you're tweaking the settings of the initial detection.

    • Multiply
      At each location the amount of punch is calculated, the result is multplied by this.

      Can be used to shift the response behavior.

    • Subtract
      Subtracts a threshold from the result of Multiply.

      A higher value means that far less audio gets a boost.

    • Rise Time
      Over how much time difference do we measure volume differences.

      Should be bigger for lower frequencies because a waveform takes more time to go up there.

    • Spread Time
      The area in which we allow the volume to go up.

      (see Initial boost) is related to the punch rise time, but may be made a bit bigger.

    • Reduce for jump above
      If the level suddenly increases more than this, reduce the amount of boost.


    Smoothing section

    Settings to avoid artifacts.

    Controls how fast the volume may go up (should be fast!) and down (should not be fast, to avoid bad effects).

    Filter smoothing panel

    The smoothing settings.

    • Rise speed
      How fast the volume may go up.

      Should be slow enough to avoid distortion, but fast enough to keep the punch.

    • Fadeout speed
      How fast the volume may go down.

      If the volume goes down too fast, ugly vibrating sounds can emerge. These times should be long, but fast enough to avoid a noticeable boost of other sounds after a punchy sound.


    Bands section

    Frequencies and slope steepness of all the frequency bands.

    Bands panel


    • Frequency
      The center frequency of each band.

    • Slope to {}
      Steepness of the left slope of the band.

      Less steepness generally gives a more natural, but sometimes harder to control sound.

    • Flat tops
      The level at which the top of this band must be cut off.

      If no compression/limiting occurs, or if all the bands are compressed/limited by the same amount, the end result is guarranteed to be flat in frequency response.

    • Slope from {}
      Slope of the right side of the band.

      Less steepness in general gives a more natural, but harder to control sound.


    Detection section

    Controls the detection of the input level.

    Level detection panel

    The level detection settings.

    • Channel separation
      Process channels separately, combined, or in between.

      At 0%, the two channels will always behave the same. At 100%, they move completely separate of each other.

    • Detection type
      Chooses between RMS or Peak level measurement.

      Peak mode can cause quite large reactions to a single small spike in the sound. RMS mode responds more like human hearing does, but low frequencies seem to be counted a lot stronger than in peak mode, which easily causes pumping.

    • Look-ahead time
      Lets the compresor respond to the sound a bit in the future.

      This means that the initial spike of a loud sound gets reduced better, which can give a more natural sound.

      The attack of the limiter is already protected, and if you don't use very short attack times for the compressor this probably has little effect.


    Non-standard tweaks section

    Settings that control compressor/limiter envelope detection.

    In a compressor we have 2 things: An 'envelope', basically a line that follows the audio level, and the compressor behavior itself. If the level drops a lot, release is faster - and this is based on the envelope. Now, if the envelope just follows sample levels, then there will be a lot of near-0 values (just when a waveform crosses 0) which would cause infinitely fast release behavior. The envelope line needs to be made such that this doesn't happen.

    So, around a peak in the waveform, for the surrounding samples we should not allow the envelope to reach much lower values than the value of that peak.

    That works fine for high frequencies. But if you take a bass, the sample values are dropping slowly and in the valleys the level will still approach 0. Which still causes issues with release behavior. Because of that, there's some code that measures DC offset and increases the Base smoothing to something close to infinity when there's more DC offset present. Base smoothing controls how big the area is that's considered for DC measurement (lower frequency = bigger area). What we are actually measuring here is DC offset in a specific direction divided by total (absolute) power.

    Non-standard tweaks panel


    • RMS block size
      The size of the area around the current sample used to calculate the RMS level.

      Bigger values means less precise timing of attack/release behavior, but also less effect from low frequencies (less pumping). Generally, the RMS block size should be set just high enough to not cause distortion when using the limiters (Threshold level) a lot.

    • Base smoothing
      Controls envelope smoothing around peaks in the waveform.

      Lower values may cause distortion, but too high values reduce the precision of the limiters and (to a much lesser extent) the compressor release behavior.

    • Base detection
      Controls upto which frequency bass should be detected for Smooth Base power.

    • Smooth Base power
      If bass is present (Base detection), increases the Base smoothing temporarily.

      This slider controls how strongly the bass affects the release behavior. Setting it higher means more release slowdown when we see bass.

      If you use this for a single multiband band, then you need less of this because there are less other frequencies that hinder bass detection.