Sound Forge Click/Crackle tool amplifies audio

2008-07-14 23:55:33

I hope someone can help me with this because I’m baffled. I simply cannot find an explanation for why it’s happening.

I am using the Sound Forge Click & Crackle Removal plugin to remove clicks from a vinyl recording. The problem is that it amplifies the audio during the process.  The original capture was already quite strong, peaking at about -0.5dB at the strongest point, but after the click removal the meters hit about +3dB.

Neither the help file nor anything I have read online suggests that an amplification/normalisation is part of this process. Is it to be expected and if so why? If it is normal, it seems surprising that the signal level should have been allowed to go above 0dB without warning. Is this a true clipping (I mean since it is calculated rather than a saturated input signal), and should I be able to recover the audio simply by re-normalising the recording?

Thanks very much for your help.

Sound Forge Click/Crackle tool amplifies audio

Reply #1 – 2008-07-15 00:12:41

You may be doing highpass filtering if the checkbox "Remove low frequency rumble" is activated. During this process the peak amplitude will change.

Only floating point sample formats allow overflow above 0 dB(Full Scale). Since you're seeing +3 peak, I assume your version of SF is working using float temp files. If this is so, 'clipped' peaks are recoverable. Whether this applies to DirectX plugins, I don't know – just try a negative gain and see for yourself.

I have used Sonic Foundry Sound Forge 6.0 together with NR v2.0h extensively and have not noticed abnormal attenuation or boost of the signal.

Sound Forge Click/Crackle tool amplifies audio

Reply #2 – 2008-07-15 21:53:52

Thanks for your response. You're right, I was removing low frequency rumble. I will try a negative gain adjustment to try to recover the true waveform. I guess I need to do this before saving as a 16bit wav, when the data will be lost.

Sound Forge Click/Crackle tool amplifies audio

Reply #3 – 2008-07-15 22:00:42

I feel it's much safer to give yourself at least 3 dB headroom – before you do any processing. I'm not sure about your version of Sonic Foundry NR, but older DirectX plugins have 24-bit I/O and may produce clipping in output.

In case you don't want to perform automatic declicking upon the entire file, highpass filtering can also be done separately using the Paragraphic Equalizer (there's even a preset for that).