Declip repairs digital and analog clipping artifacts that result when A/D converters are pushed too hard or magnetic tape is over-saturated. Declip can be extremely useful for saving recordings that were made in a single pass, such as live concerts or interviews, and any audio that cannot be re-recorded.
Oct 10, 2008 Don't be misled, the declipper in iZotope RX also produces those pops if the settings are too high. Again, RX is a good tool, but you have to make sensible use it for things to work out fine. Again, as I mentioned above, I hear artifacts in the declipped sample posted above (as in some harshness in the music). DeClip is part of Acon Digital’s Restoration Suite. It’s a very simple plug-in to use and does exactly what it says on the tin. Sadly, DeClip is not sold separately but is included in the Acon bundle of four audio restoration tools that you can buy for a shade under £80, which is pretty good value for money. Apr 22, 2017 RX 6 Advanced 301: The Unofficial Video Manual by Joe Albano Video 4 of 27 for RX 6 Advanced 301: The Unofficial Video Manual iZotope RX is by far the king of audio repairs.
Using the Histogram to set the Clipping Threshold
The histogram meter in the Declip module allows you to set the Clipping Threshold control by finding the audio level where the waveform's peaks are concentrated. This usually indicates at what level clipping is present in the file.
Setting the Clipping Threshold
Select a section of the recording where clipping is prominent, then click the Compute button. This will analyze the levels of the program material. If clipping is present in the selection, it will usually appear as a horizontal line in the histogram that extends all the way across the meter.
To set the module's threshold, move the red line in the histogram, or the Clipping Threshold slider, until the red line in the histogram is just below the line where clipping is concentrated.
Makeup Gain
Start by setting make-up gain at around -6.0 dB. This control accommodates the increased peak levels caused by the declipping process. If you're removing clipping during a short selection of a file, you may want to set this control higher to prevent a noticeable volume drop in the program material during the declipped section.
Choosing a quality mode
There are three quality modes in RX's Declip: Low, Medium, and High. Low quality mode processes very quickly; High quality mode processes slowly but in some cases can achieve better results. In many cases you will find that 'Low' quality mode gives you great results. To save time, always start by previewing the Low quality modes first. You can also use the Compare Settings window to try multiple modes and preview the results.
Read more about Declip controls in the Reference Guide.
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Overview
De-clip repairs digital and analog clipping artifacts that result when A/D converters are pushed too hard or magnetic tape is over-saturated. It can be extremely useful for rescuing recordings that were made in a single pass, such as live concerts or interviews, momentary clipping in “perfect takes”, and any other audio that cannot be re-recorded.
De-clip will process any audio above a given threshold, interpolating the waveform to be more round. Generally, the process is as easy as finding the clipping you want to repair, then setting the threshold just under the level where the signal clips.
Controls
- HISTOGRAM METER: Displays waveform levels for the current selection as a histogram. The histogram meter helps you set the Threshold control by displaying the audio level where the waveform’s peaks are concentrated. This usually indicates at what level clipping is present in the file. The longer the line for the histogram is, the more energy is present at that amplitude.
HISTOGRAM ZOOM CONTROLS: The histogram’s range can be scaled if you need a better view of your signal. Use the (+) and (-) buttons to scale your display and value resolution for the De-clip module. These buttons reduce (+) and/or expand (-) the range of the threshold slider and histogram. You may want to extend the histogram range when the clipping point is lower than what you can see on a histogram or if you don’t see anything on the histogram.
Note on histogram updating in the application vs. the De-clip plug-in
- In the RX Audio Editor, the Histogram meter updates based on selection: Select a section of the recording where clipping is prominent and De-clip will analyze the levels of the program material. If clipping is present in the selection, it will usually appear as a horizontal line in the histogram that extends all the way across the meter.
- In the De-clip Plug-in, the histogram runs as a real-time meter.
What is a histogram?
- A histogram is an analytical tool that displays how many samples are present at a given signal level over a window in time. The longer the line for the histogram is, the more energy is present at that amplitude.
- If a lot of energy tends to collect near the top and bottom edges of a waveform, that waveform is probably clipped and distorted.
- In the RX Audio Editor, the Histogram meter updates based on selection: Select a section of the recording where clipping is prominent and De-clip will analyze the levels of the program material. If clipping is present in the selection, it will usually appear as a horizontal line in the histogram that extends all the way across the meter.
THRESHOLD [dB]: Defines the level used for detection of clipped intervals. Generally, this should be set just below the actual level of clipping. To set the threshold, move the Threshold slider until it lines up with the place in the histogram just below where clipping is concentrated.
Understanding the Clipping Threshold overlays
- Adjusting the Clipping Threshold will display a blue line within the histogram and a gray line on the waveform itself (when the De-clip Threshold effect overlay). These lines indicate the audio information that will be considered as “clipping” by the de-clip algorithm.
Using the De-clip Threshold Effect overlay in the Spectrogram/waveform view
- By default, De-clip Threshold is enabled in the View > Effect Overlay menu.
- When enabled and the De-clip module is open, the De-clip threshold overly will be displayed in the spectrogram/waveform display.
- You can adjust the Threshold controls in the De-clip module by adjusting the Threshold overlay lines in the spectrogram display.
- You can use the mousewheel on the waveform amplitude ruler to adjust the threshold control values.
- Adjusting the Clipping Threshold will display a blue line within the histogram and a gray line on the waveform itself (when the De-clip Threshold effect overlay). These lines indicate the audio information that will be considered as “clipping” by the de-clip algorithm.
THRESHOLD LINK: Toggles the ability to adjust positive and negative clipping thresholds independently.
- When this option is enabled, you can adjust the positive and negative clipping Threshold controls independently. This is useful in cases where more clipping is occurring on one side of your waveform.
- You can also set asymmetric de-clipping thresholds directly from the waveform by toggling the lock box between the threshold controls on the waveform display.
- When this option is enabled, you can adjust the positive and negative clipping Threshold controls independently. This is useful in cases where more clipping is occurring on one side of your waveform.
SUGGEST: Calculates suggested threshold values based on the levels in your current selection.
QUALITY: Controls the interpolation processing quality. There are three quality modes in the De-clip module: Low, Medium, and High.
De-clip Quality mode notes
- Low quality mode processes very quickly.
- High quality mode processes slowly but is capable of achieving better results.
- In many cases you will find that Low quality mode gives you great results. To save time, always start by previewing the Low quality modes first. You can also use the Compare feature to try multiple modes and preview the results.
- Low quality mode processes very quickly.
MAKEUP GAIN [dB]: Selects the gain to be applied to the selection after De-clip.
When to use the make-up gain control
- The De-clip process causes an increase in peak levels. The Makeup gain control can be used to prevent the signal from clipping after processing. It is also useful for matching the level after processing to unprocessed audio outside of the selection.
- The De-clip process causes an increase in peak levels. The Makeup gain control can be used to prevent the signal from clipping after processing. It is also useful for matching the level after processing to unprocessed audio outside of the selection.
POST-LIMITER: Applies a true peak limiter after processing to prevent the processed signal from exceeding 0 dBFS.
- De-clip usually increases signal levels by interpolating signal segments “above” the clipping point, which can make the signal clip again if the waveform format offers no headroom above 0 dBFS.
- If the post-limiter is disabled, the restored intervals above 0 dBFS can be safely stored even without makeup gain as long as the file is saved as 32-bit float. Intervals above 0 dBFS will clip when played back through a digital-analog converter.
- De-clip usually increases signal levels by interpolating signal segments “above” the clipping point, which can make the signal clip again if the waveform format offers no headroom above 0 dBFS.
More Information
Suggestions for severe distortion
Izotope Rx Declip Brickwall 1
- For certain situations, using the Deconstruct module to extract the noise components of the distortion can help remove additional artifacts beyond the clipped peaks in a waveform.
- In cases where severe distortion is visible on the spectrogram, the Spectral Repair tool can be used to select those problem areas, and attenuate or replace them with undistorted audio.
Visual Examples
BEFORE & AFTER CLIP REPAIR
A waveform before and after clip repair. The after example (bottom) shows the original repaired waveform (faded) and the post-limiting waveform (bright).
Izotope Rx De Clip Brickwall
UNLINKING THRESHOLD CONTROLS TO CURB ASYMMETRIC CLIPPING
Izotope Rx Declip Brickwall For Sale
This problematic waveform (grey) shears off around −13 dB on only the positive side of the waveform (the histogram on the right shows the extra positive energy of clipped audio). Extra processing of the negative side would be unnecessary, so the Threshold controls can be unlinked to process above −13 dBFS on the positive side only. The resulting waveform is drawn in blue above the grey sheared peak.