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CuteStudio Ltd.

Reversing the Loudness War


Regardless of your playback equipment (iPods, car ICE, Office, kitchen or HiFi) all music is compressed at source and this can in general only be safely compressed further as required.

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The initial decompression is uncontrolled and can involve several stages at various thresholds and severities. The end result is in general something that's very difficult to recover - almost to the level of an art form - but universally tends to reduce gain and hence HF detail at the waveform extremes.

A real case of repairing loudness war compression damage


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The following is a track from the excellent Sarah McLachlan called 'In Your Shoes', a fairly modern album as evidenced by the 'professional' way the original waveform has been carefully converted into a brick shape for consumers.

If we zoom in we can see the original isn't really clipped but contains a flattened zone of data at the format extremes.
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Note the vertical scale starts at +1 to -1 which is represents the format's limits, which indicates that the mastering was done to cram as much volume onto the CD as possible.
This is the usual process but there are exceptions, some tracks from Miranda Lambert and Sia are compressed and clipped: but then put onto a CD only using 40% of the format's magnitude which is very odd indeed and rather a waste of 1 bit: They have effectively been mastered to 15bits.

Decompression: Auto mode

Switching on SeeDeClip4's auto decompression gives us this conservative fix. The fix is mild because too much decompression is easy and sounds awful: best too little than too much!

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Decompression: Manual mode

In studio we have manual mode available, so we can dial in rather more gain so the waveform detail is more or less restored, although there is still a little flattening (LF compression) that perhaps a later version of SeeDeClip4 may address.

Note that the top slider acts only as an on/off in manual mode and the 'Manual mag' is the amount of gain used. In auto mode the slider allows you to moderate the amount of active decompression.

Looking at the graph you can see I am aiming for an equal magnitude of detail at the edge of the waveform as in the middle as I'm assuming here that the HF signals should be 'riding' the bass here, rather than being continually squashed by it.
This HF signal will include Sarah's voice, cymbals, guitar etc.
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Note that we're about 3dB ahead in dynamics at this point. The waveform will look a little less like a 'brick' but not that much as the limiting used by mastering has made a lot of peaks the same level so that information has been lost.

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Decompression + Declipping

Here we've added declipping to the process, which has decided to add another 3dB of dynamic range - this time on a clip-by-clip basis thus restoring some of the original dynamics.
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We're using the broad declipping from DII (histogram detection) here so it's a fairly big change. If we unchecked DII the declipping after decompression would be just the flat tops only, so this would be largely unaltered by additional 'narrow' declipping.

Note that the Studio's 'Preview' graphs adds those purple lines when both decompression and declipping are used so you can tell where one process ended and the other began.

Summary

We now select the 'show before' graph function so we can properly compare old and new waveforms to see the result of our extra processing. You can see the original now looks rather flat and dull, the new one has the appearance of perhaps what we'd imagine the original track was like before ruining by the mastering process.

As for the sound, be aware it's very easy to ruin the sound with decompression but in the right place to the right amount it can bring a whole new level of realism to the sound that simply wasn't there on the compressed original.

This track however sounded very very good in the studio page with the repairs, Sarah in full voice cutting through the music, a more open, unconstrained sound altogether.
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Notes: When using the decompressor always bear in mind to following:

  • Do not think the setting for one track will suit another: for this reason manual decompression is banished to the Studio page only.

  • Always bear in mind for popular music there may be a Mastered by iTunes version or a Japanese JDM copy, a compilation or a film sountrack DVD or CD with a better copy on it. In general the worst quality mastering is reserved for CD remasters for the HiFi community.

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