2/27/2024 0 Comments Audio blocks comboSo for this to function as intended you must compare the absolute value of the two signals and take the greater of the two. If you do not then the AB compare cell will be comparing two signals where one can be a high level negative signal and the other can be a small positive signal so the output would be the small positive signal since it is the greater of the two. Before the signal is compared you must obtain the absolute value of the two signals. The schematic below uses the Input, AB in/out Condition, and Output cells. For that method you would simply sum the left and right using a Signal Merger cell. Other applications may be more lenient and can use the average signal between L and R to drive the detector path. This ensures that any rise in signal from either channel will ensure that the output level is reduced. The external detector path is fed with the larger signal between L and R. The following schematic image shows the PeakRMS Combo algorithm being used on a stereo signal. The graph below was generated with the default time constant settings. Playing with both the RMS and Peak detection time constants on this control can yield different results, but the default settings on the control are recommended as a starting point. However, there still is a natural decrease in signal level from the initial attack, which subjectively sounds better than the harsh peak detection. Note that the first peak is attenuated quickly (not as severe as the Peak) but much more than the RMS. The light-blue output is the Combo compressor. The purple curve is the Peak output, showing the quick attenuation of the peak, but unnatural ripple introduced by the quick attack. The Red curve is the RMS output, showing the first initial peaks still getting through to the output because the of the slower attack time constant. All three compressors have a limiting compressor curve set at -20dB. The clipped brown signal is an input sine tone at a low level, that immediately increases in level. The generated images below show the difference in output signal for RMS, Peak, and Combo compressor. Peak detectors can handle these fast spikes, but then do not have a natural sound response to the increase in signal level. Typically, there are complaints that RMS is too slow to react to fast spikes in signal input. This results in getting the “best of both worlds” with both Peak and RMS compression. Depending on the time constants used for each detection (Peak and RMS) and ADI proprietary code, the algorithm switches between using RMS and Peak detection in order to apply the compressor gain adjustment. The RMS and Peak envelope of the detector input signal are calculated. The PeakRMS Combo algorithm offers a dual-detection path. Each time a point is dragged or edited, the 33 points are re-written to the DSP. In this window, 33 points can be dragged or edited to a precise compression curve. This allows a soft or smooth transition at any threshold point defined in the compressor curve.Ĭlicking on the “Show Graph” button, opens the compressor curve editor. The RMS detector decay time in ( dB/s) is written to the DSP according to this formula: Decay / ( 96 *Fs)Ĭlicking the Soft Knee button on the compressor control, writes the 33 gain table point parameters to the DSP. The RMS detector hold time in ( ms) is written to the DSP according to this formula: Fs *Hold_Time/1000 The RMS detector time constant affecting mainly the RMS attack time in ( dB/s) is written to the DSP according to this formula: 1 - RMS/(10*Fs) The peak detector decay time in ( dB/s) is written to the DSP according to this formula: Decay / ( 96 *Fs) The peak detector hold time in ( ms) is written to the DSP according to this formula: Fs *Hold_Time/1000 Clicking this button will toggle between having soft knee enabled or disabled, and new compressor curve points will be calculated.Ĭlicking on the “Show Graph” button, opens the compressor curve editor. The max value of the decay for the RMS path is limited by the RMS time constant valueĮnables a soft knee calculation for the gain table threshold points. Controls the hold time constant used in the Peak detection pathĬontrols the decay time constant used in the Peak detection pathĬontrols the RMS attack time constant used in the RMS detection pathĬontrols the hold time constant used in the RMS detection pathĬontrols the decay time constant used in the RMS detection path.
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