When does an mp3 file "lose data"

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TroubleClef
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When does an mp3 file "lose data"

Post by TroubleClef » Sat Nov 24, 2018 10:33 pm

When I read that mp3's are "lossy", what does that really mean? I haven't really seen that described anywhere... Do they degrade slowly over time? Or when accessed/played? Or only when downsampled from a higher res file?

One reason I want to understand is that I'm trying to decide if it's still worth the effort to purchase cd's and rip to flac format, or just purchase mp3s at 300kbps for example. Currently, when I sync to my mobile device I convert from flac to mp3 at 192kbps. If I were to use that process from a 300kbps mp3 to 192kbps mp3, would the original 300kbps mp3 file be degraded?
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Peke
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Re: When does an mp3 file "lose data"

Post by Peke » Sat Nov 24, 2018 11:59 pm

Hi,
Lossy format means that whenever you re encode such format file (Convert included) quality of destination file is always little bit lower than original due the compression.

Eg. Encoding FLAC -> MP3 -> FLAC will not give you same FLAC file but Degraded one. Same applies to MP3 300 -> MP3 300 if you for example apply Volume Leveling which forces re encode.

FLAC -> WAV -> FLAC do not loose any quality as they are lossless formats.
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TroubleClef
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Re: When does an mp3 file "lose data"

Post by TroubleClef » Sun Nov 25, 2018 2:25 am

Thanks for that info. How about in the scenario where I have an mp3 300 in MMW library and sync/convert to mp3 192 in MMA, is the original mp3 300 in the library degraded? Or if I change tags or album art, does that degrade files either in the library or MMA?
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Peke
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Re: When does an mp3 file "lose data"

Post by Peke » Sun Nov 25, 2018 5:03 pm

Hi,
NO, your Source file in MMW will not degrade, also Tagging (Album art included) will not degrade Audio Data, only Convert Format and Files in MMA will be slightly degraded due the lower bitrate, but unless you play them on higher-end headphones/speakers you will not hear the difference and usually when you have high-end headphones/speakers users tend to use FLAC as playback source.

Also difference from FLAC and MP3 192 should be noticeable, at least I hear it.
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TroubleClef
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Re: When does an mp3 file "lose data"

Post by TroubleClef » Sun Nov 25, 2018 6:18 pm

OK, thanks this is helpful. So if I understand right, once you create the mp3, all the losses have already taken place and it is what it is no matter if you play it, tag it, move it, sync it, etc?

I always keep the flac files in my library so I can convert to mp3 for mobile use and not have to worry about going back the other direction... But do you think its worth the effort to rip a cd to flac for my library rather than just buy 320mbps mp3 directly?
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Re: When does an mp3 file "lose data"

Post by rivorson » Sun Nov 25, 2018 7:59 pm

That's correct, all the loss of quality is done when the file is created, though as Peke says it's unlikely you'd hear any difference if encoding above 300kbps. Playing the file and changing the metadata doesn't change the audio contents in any way.

Whether it is worth ripping the CD or buying the mp3 depends on your circumstances.
Pro mp3:
  • Flac is much larger than mp3 so if you have a laptop with limited storage then the mp3 would be good.
  • The difference between flac and a 320kbps mp3 is imperceptible.
  • Doesn't require additional conversion to use on other devices like phones.
  • Most mp3s already have metadata at the point of purchase. Ripping a CD relies on FreeDB having the metadata for the CD and then checking that it is correct.
Pro flac:
  • Keeps the full quality of the source audio.
  • mp3 is 25 years old now. There are better formats available.
  • Can be converted to any other format in the future. For example if you decide that you'd rather use aac audio on your phone next year then you can just change your auto convert settings and have that format.
  • If either format stops being supported in the future, flac can be converted to another lossless format and still retain full quality. Converting mp3 to another lossy format would result in additional loss.
  • If you already own the CD then ripping it can be done with no additional cost.

TroubleClef
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Re: When does an mp3 file "lose data"

Post by TroubleClef » Sun Nov 25, 2018 10:23 pm

That is an excellent breakdown, thanks! The greater compatibility of flac going forward as an archival format seems like one of the most convincing reasons. All the cd's I own are already ripped to flac so I'm thinking of future purchases when considering cd to flac vs mp3. Sometimes the cd's are actually cheaper so its more the question of the time to rip and all...
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Re: When does an mp3 file "lose data"

Post by Peke » Mon Nov 26, 2018 7:05 am

rivorson wrote:
Sun Nov 25, 2018 7:59 pm
[*]The difference between flac and a 320kbps mp3 is imperceptible.
I can argue on that as for example I NOW have Audio Technica ATH-M70x and TASCAM US 2x2. Difference is clearly distinguishable. Even FLAC are 16/44.1 directly RIP from CD.
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Lowlander
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Re: When does an mp3 file "lose data"

Post by Lowlander » Mon Nov 26, 2018 12:08 pm

Double blind testing tended to show users can't distinguish quality differences above 192kbps MP3. The double blind is important as when you know what you're playing you'll perceive a difference as you know there is a quality difference.

That said, I'm on FLAC myself and I "perceive" a difference too.
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TroubleClef
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Re: When does an mp3 file "lose data"

Post by TroubleClef » Tue Nov 27, 2018 11:01 pm

Peke wrote:
Sat Nov 24, 2018 11:59 pm
Hi,
Lossy format means that whenever you re encode such format file (Convert included) quality of destination file is always little bit lower than original due the compression.

Eg. Encoding FLAC -> MP3 -> FLAC will not give you same FLAC file but Degraded one. Same applies to MP3 300 -> MP3 300 if you for example apply Volume Leveling which forces re encode.

FLAC -> WAV -> FLAC do not loose any quality as they are lossless formats.


When you to volume leveling forcing a re-encode, are you talking about the settings during a cd rip, or the setting in MMA?
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Re: When does an mp3 file "lose data"

Post by Peke » Wed Nov 28, 2018 9:08 pm

Hi,
No, I'm talking about regular convert and conversion using single example FLAC file or MP3 file.

Lossy conversion:
1. Source FLAC file
2. Convert to MP3 320
3. Convert Converted MP3 32 (Step 2) to FLAC
4. Compare source FLAC with FLAC result from Step 3 get degraded Quality

Example 2:
1. Source MP3 32 file
2. Convert to MP3 320
3. Compare source MP3 320 with MP3 320 result from Step 2 get degraded Quality


Lossless conversion:
1. Source FLAC file
2. Convert to WAV
3. Convert Converted WAV (Step 2) to FLAC
4. Compare source FLAC with FLAC result from Step 3 they are bit to bit same eg. no quality degradation

Leveling Audio Data (Analyze is not leveling as it just add GAIN index to TAGs) will always change Audio data and Quality is debatable, for quality testing you always do simple convert without any post processing.
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TroubleClef
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Re: When does an mp3 file "lose data"

Post by TroubleClef » Wed Nov 28, 2018 11:47 pm

Thanks again, that is all really helpful information. If you don't mind a couple more questions, when you say "analyze" are you referring to the playback setting in MMA? Also, can you give me an example of a few settings that would be considered "post processing"?
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Re: When does an mp3 file "lose data"

Post by Peke » Thu Nov 29, 2018 8:07 pm

Hi,
Analyze -> Read and analyze Audio data from file to calculate Volume Gain Index
Post Processing -> General All Media term (Pictures, Audio, Video) not just MediaMonkey when some thing is changed to original source re-encode, Volume Leveling (includes re-encode), Format change (unless it is lossless), Effect adding, ...
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