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Question about clipping


zonka
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Sorry for a silly question. If a flac track clips does that mean the literal file is cut off at the top or does that point in the file extend above the threshold (whatever that is)? In other words, if I lower the gain will I get the "whole" track now without clipping or are those peaks cut off for good?

 

I don't even know if I'm phrasing this correctly - I apologize if it is hard to understand.

 

Thanks for any light someone can shed.

Drew

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Sorry for a silly question. If a flac track clips does that mean the literal file is cut off at the top or does that point in the file extend above the threshold (whatever that is)? In other words, if I lower the gain will I get the "whole" track now without clipping or are those peaks cut off for good?

 

I don't even know if I'm phrasing this correctly - I apologize if it is hard to understand.

 

Thanks for any light someone can shed.

Drew

 

The problem exists with any lossless PCM file, whether it is FLAC, WAV, AIFF, or some other format. Unfortunately, there is no clear cut answer to your question with the information you provided. If the original analog signal had clipped the A/D converter then the distortion would have been encoded into the original digital recording. Whether this amounted to serious (audible) distortion will depend on the amount of clipping and the type of music. The amount of clipping refers to the signal amplitude that would have been represented if there had been no digital clipping. This information is not available to you at this point. However, if there is significant clipping then there will be several consecutive samples that are at the maximum. This is usually a good indication that there was serious amounts of clipping.

 

It is possible for a recording to have many samples that are exactly at the peak amplitude. This will happen, for example, if a master file is normalized. In this case there would be no distortion in the recording. However, even if the recording has no distortion on it, your system playback may still end up distorted. This can happen in your computer, especially if the computer does any signal processing (e.g. EQ for room correction) or if your DAC upsamples (most do) and has its gain set to maximize measured signal to noise ratio, allowing "intersample peaks" to become distorted. In addition, the DAC will have op-amps and these may have distortion at high levels. You can isolate the cause of the distortion by reducing the gain digitally in the computer. One way is to take an editor and simply reduce the gain in the file by a few dB. (Best to convert to 24 bits first before doing this or you will lose resolution.) In some cases you can use an operating system digital volume control to fix the problem. Some DACs also come with a digital volume control option and this may eliminate DAC overload on problem recordings. Of course, if the problem is with your amplifier (beyond the volume control) you can eliminate this by turning down the volume.

 

If I had a copy of the file I have the software and expertise to analyze the file and tell you whether the problem is with the recording or with your system. It would also be helpful to know what your player software, O/S, and DAC are (and in the case of some DACs how they are set up).

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Great reply - and thank you. This makes sense to me. The foobar DR meter came back with 3 different tracks with a peak of 0.0 with rest of tracks under the ceiling. I don't hear any distortion - I just see very slight clipping, in red, in audacity (very little). I could probably just leave it alone or drop it a few dbs and everything will be fine.

Thanks again for your detailed post.

Drew

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Sorry for a silly question. If a flac track clips does that mean the literal file is cut off at the top or does that point in the file extend above the threshold (whatever that is)? In other words, if I lower the gain will I get the "whole" track now without clipping or are those peaks cut off for good?

 

I don't even know if I'm phrasing this correctly - I apologize if it is hard to understand.

 

Thanks for any light someone can shed.

Drew

Hi, Drew -

 

What's hard to understand is where you're seeing this - during recording? playback? converting FLAC to mp3, etc? You seem to be describing visible clipping in Foobar's output level meter when listening to your files, in which case the files themselves are not being altered. If you talk into a microphone and the PA distorts, it changes what is heard through the PA but it doesn't change your own voice. You could take the time to go back and normalize these tracks with recording software (e.g. Audacity, which has a very easy to use normalizing function), but that seems like a lot of work with no potential benefit if you don't hear any problems. If all your rips are like this, you may have ripped at just a bit too high a level - some USB preamps have a level control on the digital output (e.g. the Parasound ZPhono USB) to optimize this.

 

Foobar has a function called replaygain that will "fix" this for you while playing, and it doesn't alter the source files at all. From an excellent 2012 post by Lord Crow on HeadFi:

 

"Track Gain: increases or decreases the volume of that track to on average 89 dB. All tracks will be at about the same loudness.

Album Gain: increases or decreases the volume of the album to be on average 89 dB. This allows quiet tracks on the album to remain quieter than the loud tracks on the album.

 

Basically if you listen to an entire album at a time, you should use 'Album Gain'. If you listen to shuffled/random tracks, you should use 'Track Gain'.

 

If your albums are arranged by folder then you first want to go to Preferences -> Context Menu -> ReplayGain and select "Scan selection as albums (by folders)". That way if you scan two albums with the same metadata but in different folders they will be treated as from different albums. Look at the top of your library, right click 'All Music', select ReplayGain and then 'Scan selection as albums (by folders)'. Scanning gives both track and album gain. If your music isn't organized by folders you can just scan by tags.

 

Once that is done and you update the tags (the whole process can take awhile with a big music collection) then go to Preferences -> Playback and under ReplayGain select if you want track or album gain and then use 'apply gain' under Processing. You could use 'apply gain and prevent clipping according to peak' to prevent clipping but I use the Advanced Limiter DSP (Preferences -> Playback -> DSP Manager). Don't think there would be a difference either way just that the Advanced Limiter will work on tracks without ReplayGain.

 

All the ReplayGain data is stored in tags and can be removed or just turned off in foobar.

 

Barry Diament provides an excellent discussion HERE in the 6th or 7th post in the linked thread. His conclusion is worth repeating here: "Personally, I'd rather use my volume control."

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