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Jason Hutchinson5-Aug-20 1:58

Jason Hutchinson

5-Aug-20 1:58

The MP3 codec is a lossy format. Unfortunately, there is no way back to the original file size without loss. The only real way to fix it would be to encode them at the desired bitrate from uncompressed WAV files.

dandy725-Aug-20 4:34

5-Aug-20 4:34

Jason Hutchinson wrote:
The MP3 codec is a lossy format. Unfortunately, there is no way back to the original file size without loss.

Well, the file started life as 128kbps, then was converted to 320kbps. The question is, how much loss would be incurred when going from 320 back to 128, and comparing that version with the original that already was at 128. Even though, I realize, he no longer has it.

But it would be an interesting experiment one way or another - and hang on to all versions each step of the way so they can later be compared.

mngerhold5-Aug-20 3:03

mngerhold

5-Aug-20 3:03

Send him here: mp3ornot.com[^] and if he doesn't score (say) 5/5 then he may as well give up, and encode them all to 128. I got the first 2 right, but failed on the third (didn't like the sound anyway) so stopped. I am not an audiophile.

dandy725-Aug-20 4:40

5-Aug-20 4:40

That's an interesting test, although they really need more than just the one sample song. Some recordings can sound fine at 128kbps, and others might sound terrible at that resolution.

But then I've only tried this with my desktop speakers with the window open, traffic going by and a fan running. Not exactly a great listening setup.

mngerhold5-Aug-20 4:44

mngerhold

5-Aug-20 4:44

There is more than one sample - by some magic, if one waits, the sample changes on next play - don't ask me how that works! I think you have to do all 3 listens, then select an answer - then the clip changes!

dandy725-Aug-20 4:54

5-Aug-20 4:54

I hit refresh about 20 times, and the same sample keeps coming up. Maybe you do have to listen to them all, rather than immediately jumping to step 2.

[Edit]
Ok, my mistake was hitting Refresh to try to get a new sample. It seems to restart the whole thing, so refresh is entirely pointless...

kholsinger5-Aug-20 5:16

kholsinger

5-Aug-20 5:16

I think you can tell by looking at the frequency content. It's easy to tell the difference between an "it started as an MP3" file and a "it started as a WAV" in my audio noise clean-up software because the spectrum for the MP3 has a brick-wall low pass filter well below the Nyquist frequency for the file's sample rate. That frequency is probably lower for lower-resolution MP3 files. (But no, I don't think I've ever checked this. And though I'm working from home, I risk far too much distraction from "I'm supposed to be working now" if I turn on the home computer and its associated audio editing tools to run some tests.)

mngerhold5-Aug-20 5:44

mngerhold

5-Aug-20 5:44

I wondered if the frequency spectrum would be enough to indicate the bit rate, as although I knew that MP3 encoding 'threw away' bits of the sound, I didn't know whether that would show clearly on a spectrum - so I just took the same 5s clip from the sound track to Clockwork Orange (The Thieving Magpie) which I know contains some well defined high-frequency bits (a flute or somesuch - I used this track to compare recordings onto audio cassettes many years ago, to establish which tape quality (cost) level was needed to avoid unacceptable loss). I loaded the orignal WAV file from CD into Audacity, and did a spectrum. Then saved as MP3 at a variety of bitrates. and did the same. Without being able to load pictures here, I can table the maximum frequency seen in the plots for various bit rates, as it is very clear there is a pattern:

bit rate    -100dB freq (Hz)
Full (WAV)   21,300
320 kbps     20,100
256          19,400
128          16,600

I picked the freq at which the signal went below -100dB, as that corresponded roughly with the visual scale on the plot (which only goes down to -90 by default). The cutoff was well-defined, and if there is a place to put them, I can supply screen shots.

So one could take a resampled file and, if its frequency cutoff (of maybe a suitable bit) was below, say, 18kHz, one could judge that it came from a 128kbps original. It would be a lot of work to do that for all files, of course. You really need a tool that measures in one go the frequency cutoff.

What surprised me was that there was very little difference in the spectrum apart from the upper end - but of course, that is where the sample rate required for faithfull reproduction is greatest, so where the greatest reduction in file size can be obtained. Now off to look at the wavefoms in more detail...

I, of course, am retired, so have nothing better to do - and it was fun.

kholsinger5-Aug-20 6:23

kholsinger

5-Aug-20 6:23

Thanks for confirming my hunch.
WAV file from CD should be sampled at 44.1KHz, which puts Nyquist at 22.05KHz -- pretty close to the 21,300Hz you see. My older ears don't hear the difference between 128kbps and 320kbps unless I'm paying close attention.

Furkan Omay5-Aug-20 19:22

Furkan Omay

5-Aug-20 19:22

You can compare decoded raw bitstreams with tools like Audacity but imho it is unnecessary.

Re-encoding with VBR (Variable bitrate) encoding would be the way to go. It will use lower bits when there is less sound information, and will use your maximum provided bitrate when it actually needs it.

Also, I would strongly advise to migrate from mp3 to a better format unless you're hardware locked.
128 kbps opus is said to be transparent (almost indistinguishable from uncompressed form to 99% ears) while 80-96 kbps opus is somewhat equivalent to 320 kbps mp3. And the format is royalty-free with wide support from various OSes.

dandy726-Aug-20 8:18

6-Aug-20 8:18

Never heard of Opus until now. If I can't throw something at a random player and have it "just work", it's not even a contender in my book.

I'm reading that "[...] in many respects Ogg Opus is the successor to Ogg Vorbis". That name, I recognized, and I stopped reading there.

You can have the most awesome format in the world, if the support isn't there, it's a non-starter. Re-encoding is never a good idea, and going down this path to me sounds like having to re-encode in a different format every couple of years for the sake of using the format-du-jour. No thanks.

patbob11-Aug-20 7:56

patbob

11-Aug-20 7:56

No, there will not be any such software. In short, your friend cannot return to their original 128k quality files from what they have now.

The process you're referring to is called transcoding. Whenever you transcode across bitrates of a lossy codec, you lose information because the quantitization of the samples is different. So, quality was lost in the 128k -> 320k trancoding. More quality will be lost doing another transcoding from 320k -> 128k.

Maybe your friend is now at a financial point in their life where they can afford to replace the mangled files?

I live in Oregon, and I'm an engineer.

dandy7211-Aug-20 8:13

2 major explosions in Beyrouth

11-Aug-20 8:13

patbob wrote:
Maybe your friend is now at a financial point in their life where they can afford to replace the mangled files?

There's "affording" the time, and "affording" the money. Despite the old saying, I hope you're not suggesting both are interchangeable.

Maximilien4-Aug-20 8:50

Maximilien

4-Aug-20 8:50

Hope all our Lebanese friends are safe and sound.

Rose | [Rose]

I'd rather be phishing!

OriginalGriff4-Aug-20 9:02

OriginalGriff

4-Aug-20 9:02

For those that haven't seen it yet: RAW VIDEO: Beirut blast caught on camera - YouTube[^]

Good luck to all there, not just CP members - that's one big explosion. Rose | [Rose]

"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
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Daniel Pfeffer4-Aug-20 10:28

Daniel Pfeffer

4-Aug-20 10:28

From the angle shown, it looks like a fire, that set off the explosion. Someone's ammunition dump go up in smoke?

NOT a good day for civilians in Beirut. Sigh | :sigh:

EDIT: according to the Israeli web site www.ynet.co.il (the web site of a major Israeli paper), the small explosions were set off by a fire in a warehouse storing fireworks. The big explosion occurred when the fire reached a warehouse containing a few tons of nitrates. Nitrates, for those who've forgotten their chemistry, are the starting point for chemical fertilizer and also for explosives.

Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.

OriginalGriff4-Aug-20 10:41

OriginalGriff

4-Aug-20 10:41

Daniel Pfeffer wrote:
NOT a good day for civilians in Beirut.

Slight understatement there - the airport (10km / 6 miles from the blast) was damaged ... Latest I've seen is 50 dead, 2750 injured, but they are still looking for the firemen / firewomen who were working on the original blaze. 90% of the wheat for the Lebanese staple flatbread is imported throughn the now destroyed port. And with the recent economic fun-and-games in Lebanon, it's all just going to make a very bad situation much, much worse.

Daniel Pfeffer4-Aug-20 11:16

Daniel Pfeffer

4-Aug-20 11:16

OriginalGriff wrote:
90% of the wheat for the Lebanese staple flatbread is imported throughn the now destroyed port.

It's worse than that. The big building near the port looks like a grain storage silo. A still picture from another angle shows that the silo was damaged, so even if grain were delivered, they have nowhere to store it!

The two closest ports which have grain-handling facilities are Haifa (in Israel), and Latakia (in Syria). The questions are (a) whether they have the combined additional capacity to handle the grain destined for Lebanon, (b) whether the Lebanese government will accept aid coming via Israel, and (c) whether Hezbollah will interfere with any shipments coming from Israel.

Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.

OriginalGriff4-Aug-20 11:36

OriginalGriff

4-Aug-20 11:36

Technically, I think Lebanon is still at war with Israel - I just checked and there has been a cease fire in effect since '07, but there is still border fun-and-games plus Hezbollah working in Lebanon - and as for Syria ... they are still having a civil war, plus what's left of ISIS waiting for an opportunity. Sigh | :sigh:

Couldn't have happened in a worse place at a worse time, I guess. What a mess.

Daniel Pfeffer4-Aug-20 12:06

Daniel Pfeffer

4-Aug-20 12:06

OriginalGriff wrote:
Technically, I think Lebanon is still at war with Israel - I just checked and there has been a cease fire in effect since '07

Yes, we are technically at war, but Israel has already offered humanitarian assistance including treatment of wounded in Israeli hospitals.

There are logistical and security issues, but I can't imagine the Government refusing to allow the transfer of humanitarian aid to Lebanon via Israeli ports. I expect that many Israelis (myself included) wouldn't stand for it.

Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.

Nelek4-Aug-20 21:28

Nelek

4-Aug-20 21:28

Daniel Pfeffer wrote:
I expect that many Israelis (myself included) wouldn't stand for it.

I think the biggest risk is not coming from Israeli "normal" people having something against it.

Morons, idiots and wasted souls are everywhere...

M.D.V.

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