GPU DeClicker : Remove "clicks" from audio files

GPU DeClicker is a free program for Microsoft Windows systems to remove "clicks", "pops", "bit rots" and other types of noise from audio files.

Designed primarily for audio files recorded from vinyl disks, GPU DeClicker removes noise from any supported audio file you throw at it.

The current version of the program is listed as beta. While it works fine as it is, it comes without graphical user interface as this is still on the developer's to-do list.

Note: The application supports a GPU-mode which requires a CUDA compatible graphics card and driver. It falls back to CPU processing if a compatible video card is not detected.

GPU DeClicker review

GPU DeClicker is a command line program. Audio support is powered by libsndfile and limited to formats such as WAV, AIFC, PAF, FLAC or VOC but not common formats such as MP3 or AAC.

This means that you need to convert files that you have to a supported format to have them processed by GPU DeClicker.

Use of the program is straightforward. Use the command declicker.exe PathToAudioFile to process the selected audio file.

GPU DeClicker supports parameters that you may use to target specific noise types:

• -h K -- Defines the length of samples the program uses to calculate the prediction error rating for the current sample. A larger sample length improves error detection and increases the processing time.
• -I N -- Prevents the replacement of sequences that are longer than N samples. Developer suggests to use N=8.
• -t M -- Sets the threshold for detecting bitrots and other noise types. Default is 3.
• -n -- Turns of GPU use if supported by the PC.
• -c O -- Sets the number of coefficients for noise detection. Default is 4. Quality increases with the number of coefficients but processing time increases as well.
• -r P -- Sets the number of coefficients for noise restoration. Default is 16.

You may use one or multiple parameters or none at all if you want the audio file to be processed using the default parameters.

Closing Words

GPU DeClicker is a specialized program. It is held back by the lack of support for popular audio formats and a missing graphical user interface. The latter is on the author's to-do list and things should improve once it is added to the program.

The program needs batch processing support for files. While you can create a batch script to process all audio files of a directory, using a GUI for that is a lot easier.

If you have audio files, e.g. vinyl disk recordings, you may want to try GPU DeClicker to correct recordings with "click" noises and other types of noise.

The DeClicker module is effective in dealing with clicks and fallouts of sounds. It works in real time mode (the result of the program's operation is heard immediately when playing an audio file).

It can be used not only to restore old records (for example, on vinyl records), but also to eliminate such sharp sounds as a guitar rattle, unexpected interference from bad contact of connectors, and also snapping when synchronizing multiple audio devices. In addition, it is able to eliminate sound loss (typical for tape records) lasting up to 60 samples.

It should be noted that DeClicker is not designed to deal with long series of short clicks. In order to eliminate this kind of constant noise, DeClicker should be used in conjunction with a squelch.

The principle of the device is a special algorithmic analysis of the audio signal, as a result of which clicks are detected. The nature and location of all clicks found are listed.

The sensitivity of the analysis is controlled by the parameters Mode and Threshold.

Then, the click suppression algorithm is applied to the generated list. This process can be visually observed on the DSP-Performance display screen in the DeClicker module window, which helps to fine-tune the parameters. A sound not specified by the algorithm as a click will not be subjected to any processing.

In most cases, a useful signal located in the click zone will be irretrievably lost when the click is removed. This will cause a loss of sound. DeClicker is able to automatically restore part of the wave. It is this ability that can be used to restore sound in tape recordings. The duration of such failures, which are still amenable to processing, can reach 60 samples (about one millisecond at a sampling frequency of 44.1 kHz).

Before applying the DeClicker module, you should not process the signal with high-pass filters, since in this case, clicks will become more difficult to detect.

To work in real time, WaveLab requires a Pentium 133 MHz or higher and 16 MB of RAM (better than 32 MB).

Consider the purpose of the controls located in the module window.

When the Audition button is pressed, only the signal to be deleted is sent to the module output, that is, directly clicking, and if the Deplop control is output from the leftmost position (i.e. turned on), the output of the low-frequency signal range. This mode is used to diagnose the quality of the processing performed.

The four modes that can be selected in the Quantity - Quality section are for adjusting the degree of signal processing. The higher the number of the mode, the higher the quality of removing the clicks and restoring the sound. And, of course, the more CPU resources are required.

The Threshold knob adjusts the amplitude of the clicks from which they will be noticed by the program. In most cases, DeClicker finds more clicks than you perceive by ear. Therefore, first set a high threshold value, and then listen to the threshold should be gradually reduced to the required value, in order to remove exactly what you need.

In addition, a special low-pass filter Deplop (Elimination of spoilers) that works with signals below 150 Hz is configured. It helps to get rid of such a sound interference, like spitting, which sometimes appears after removing clicks.

The buttons of the Mode section are intended for tuning for different kinds of sound material. Old is used to restore "antiques", old records with a limited content of high-frequency components. Standard - for a wide range of audio data (this mode should be tried first). Modern - for current recordings with a wide frequency range.

The DSP-Performance display is used when setting the Threshold and Quantity-Quality parameters. If the curve gets to the top of the window, it means that the maximum of the parameter is reached and the algorithm can not cope with all clicks available in the record. Then you should reduce the value of Quantity - Quality. Note that not every peak of the wave visible in the display is a click.

The DeClick-Performance display shows two curves: red shows the original raw material, and green indicates the signal after processing. This display determines the quality of the processing. If it is not executed (for example, there are no clicks in the record), the green curve is superimposed on the red one and completely closes it. When the click is removed, the red curve appears. In this case, the difference between the input and output signals is clearly visible (for illustration purposes, it is somewhat exaggerated in the display).

In the right part of the window there is a virtual indicator of the output signal level. The firm releases DeClicker in both mono and stereo versions (in our picture, a monovariant is depicted). By the way, processing each channel separately can give the best effect, because the settings will be performed separately.

The method of working with DeClicker is as follows.

First, select the Recognition Recognition mode. In most cases, it is necessary to start the work, as already mentioned, from the Standard mode. Set the Quantity - Quality parameter to the higher value (4). Threshold set to 50%. If such settings do not give an acceptable result, experiment with the options, comparing them with the original when the Audition button is on and off.

When combining the Old mode and the extreme positions Threshold and Quantity - Quality, you can achieve an interesting effect of mitigating the attack of percussion and wind instruments.

During the operation of the module, the signal delay inevitably arises, so that if there is no phase shift in the stereo signal, you must put each module in modulo if the program is used in the mono version.
In addition to its direct function, the module can be used to process recordings with noticeable distortions (with truncated signal peaks). It can somewhat flatten the truncated peaks by interpolating the signal.