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Topic: What is wrong with this conversion? (Read 4110 times) previous topic - next topic
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Re: What is wrong with this conversion?

Reply #1 –
Quote from: mark-s on
It does not look right to me. Could you please tell me what I am doing wrong?

The spectrum looks different because its an mp3 file.  That is normal.

Alt-presets are more than 10 years old.  You may want to check if an updated version of your software is available or if more modern settings are available though. 

Re: What is wrong with this conversion?

Reply #2 –
Quote from: saratoga on
The spectrum looks different because its an mp3 file.  That is normal.
So it is no problem that the frequency was cut off at about 16 kHz? I found this article about MP3 quality: http://www.walterdevos.be/how-to-check-quality-of-mp3-file

This is from the article: "You can always spot a bad quality 320 kb/s MP3 by looking at the spectrum analyzer, but you can only be sure of the cause of the degradation when you see a very obvious 16khz (or less) cutoff."

Quote from: saratoga on
Alt-presets are more than 10 years old.  You may want to check if an updated version of your software is available or if more modern settings are available though. 
Unfortunately, there is no update. What new features are missing in this version?

Re: What is wrong with this conversion?

Reply #3 –
Quote from: mark-s on
Quote from: saratoga on
The spectrum looks different because its an mp3 file.  That is normal.
So it is no problem that the frequency was cut off at about 16 kHz?

Well, the setting you tried to use doesn't include the low pass you ended up with (IIRC), so its possibly a problem that your software didn't do what you thought it would do.  You might want to check on that. 

Quote from: mark-s on
This is from the article: "You can always spot a bad quality 320 kb/s MP3 by looking at the spectrum analyzer, but you can only be sure of the cause of the degradation when you see a very obvious 16khz (or less) cutoff."

No that is wrong. 

Re: What is wrong with this conversion?

Reply #5 –
Well that site has just enough stuff right in it to make the totally wrong parts sound credible.

Quote
Notice the difference in this 128 kb/s compressed file. All frequencies above 15,8 khz are gone (black). That’s because most MP3 encoders apply a “filter” on the sound before compressing it. Yes… This has absolutely nothing to do with psychoacoustics, but is just a rude filter that almost all encoders use.

Ugh!

Read this to start: http://wiki.hydrogenaud.io/index.php?title=High-frequency_content_in_MP3s

And yes, encoders apply lowpass filters before encoding, but it's because bad things will happen if they don't! It partly does have to do with psychoacoustics, it's partly due to not enough room being in the file, and at low bitrates it's due to needing to cut the output sample rate. The highest frequencies matter the very least, so they are the first to go; they are 99.9% masked or inaudible, and keeping them is expensive (they require a lot of space and quality must be reduced in the far more audible bands).

Quote
Actually during my investigation I stumbled upon some annoying properties of Fraunhofer’s MP3 encoder. It seems that even with cutoff filter disabled (or set to 22kHz), the 320kb/s file (from the same original source as the image above) is somewhat filtered. There is a noticable “cutoff” line that isn’t present in the original file. Though the filtered 128 kb/s file will look flattened, this one still has some high frequencies in it.
Indeed, when a lowpass filter is not used, the encoder still may be very selective about which of the highest frequencies it lets through. This is by design. That said, forcing the encoder to include frequencies it is not tuned for is almost certainly going to degrade quality in the parts of the spectrogram that this guy is completely ignoring. He thinks because the visual difference is so great in the topmost frequencies, that's what he needs to be worried about... he's wrong!