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Need Info re Converting mp3 to WAV with iTunes

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Need Info re Converting mp3 to WAV with iTunes

Postby George Tyndall » Sat Nov 06, 2010 3:18 pm

I long ago discovered that, when creating and editing slide shows with PSE, WAV files work much better than MP3s.

So, whenever I would find a track on iTunes or Amazon that I wanted to use for a show, I would download it into iTunes and then right-click on it to convert it from an MP3 to a WAV file. (The newer versions of iTunes do not allow this, and that is why I still use an older version.)

What I still do not understand are the following 2 questions:

1) If I create, say, a 49MB WAV file from, say, a 4MB MP3 file, the WAV file does seem to sound slightly better; but shouldn't it be impossible to recover the data that was lost during the process of compressing to mp3?

2) If the answer is "yes, it's only in your imagination that the WAV file sounds better," then why does the 4MB mp3 file not convert instead into a 4MB WAv file, in other words, what does the extra 45MB consist of?

#-o
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Re: Need Info re Converting mp3 to WAV with iTunes

Postby Bobby » Sat Nov 06, 2010 4:05 pm

1) You cannot recover the data. Garbage In, Garbage Out. It is gone forever in a lossy compression scheme.

2) According to
http://en.wikipedia.org/wiki/MPEG_Audio_Layer_3 :

"The compression works by reducing accuracy of certain parts of sound that are considered to be beyond the auditory resolution ability of most people. This method is commonly referred to as perceptual coding.[13] It uses psychoacoustic models to discard or reduce precision of components less audible to human hearing, and then records the remaining information in an efficient manner."

The point is that the compression scheme does eliminate a lot of sound information that IN THEORY cannot be heard. But most people listening to both can detect a reduction in the depth of the soundstage, along with other issues.

And, by the way, what are the problems with mp3 and PRE? I use them all the time...
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Re: Need Info re Converting mp3 to WAV with iTunes

Postby George Tyndall » Sat Nov 06, 2010 4:15 pm

Bobby wrote:And, by the way, what are the problems with mp3 and PRE? I use them all the time...


A routine part of my workflow when creating slide shows with PSE is to use the "Fit Slides to Audio" option, and whenever I've tried to do this with an MP3 instead of a WAV file, it would not work correctly when I would perform additional editing.

However, now that I think of it, that was with PSE4, and I have not tried the method with either PSE7 or 9. I will try again as it is very appealing to have my shows consume less HDD real estate.

In addition, there would no longer be a reason for me to continue to use an old version of iTunes.

BTW, what do the extra 45MB of data consist of when I do the conversion from mp3 to WAV?
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Re: Need Info re Converting mp3 to WAV with iTunes

Postby Bob » Sat Nov 06, 2010 4:48 pm

In addition, MP3 compresses in a lossy format and a higher bitrate mp3 will sound better than a lower bitrate mp3.

WAV is a container file format which can contain audio in different formats. Usually, the format used in wav files is Pulse Code Modulation (PCM) which is uncompressed and lossless. PCM is the standard format for digital audio in compact discs. However, you can also store lossy formats in wav files as well -- including mp3. It depends on what you are using to create the wav and what options it gives you. Assuming that your wav file is using PCM (the most likely scenario), the extra 45 MB comes from uncompressing the MP3 file.
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Re: Need Info re Converting mp3 to WAV with iTunes

Postby George Tyndall » Sat Nov 06, 2010 5:21 pm

Bob wrote:In addition, MP3 compresses in a lossy format and a higher bitrate mp3 will sound better than a lower bitrate mp3.

WAV is a container file format which can contain audio in different formats. Usually, the format used in wav files is Pulse Code Modulation (PCM) which is uncompressed and lossless. PCM is the standard format for digital audio in compact discs. However, you can also store lossy formats in wav files as well -- including mp3. It depends on what you are using to create the wav and what options it gives you. Assuming that your wav file is using PCM (the most likely scenario), the extra 45 MB comes from uncompressing the MP3 file.


Bob, here is the description of a file that I just downloaded from iTunes: Kind: Purchased AAC audio file; Size: 9.7MB; Bit Rate: 256kbps; Sample Rate 44.100kHz.

And here is the description of the WAV file that iTunes just created from that file: WAV audio file; 49MB; 1411kbps; 44.100kHz.

Please elucidate.

Thank you.
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Re: Need Info re Converting mp3 to WAV with iTunes

Postby Bobby » Sat Nov 06, 2010 5:50 pm

George Tyndall wrote:...BTW, what do the extra 45MB of data consist of when I do the conversion from mp3 to WAV?...


It is just that the WAV files are not compressed. The conversion program creates an uncompressed data stream but there is no additional sonic information - just bits.

For example: using simple run-length-compression (lossless)

AAAAAAAAAA

can be compressed to

<10A>

and then uncompressed to

AAAAAAAAAA

The original (uncompressed) just contains redundant information. A more valid example using a lossy compression technique:

ABCDEFGHIJ
to
<string start A end J> (this is nonsense, just an example - don't count the bytes)
might expand to
ABDCFEGHIJ

The middle part is filled in, but not exact. More bits in the result, but no more significant than the compressed data.
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Re: Need Info re Converting mp3 to WAV with iTunes

Postby Bob » Sat Nov 06, 2010 6:00 pm

AAC is a more recent format than MP3 and more flexible for content producers, but it's very similar to MP3. It's often said that AAC was designed to be MP3's successor. AAC also uses perceptual filtering (but improved over that used in MP3) and a lossy compression scheme. But, it has better handling of transients and high frequency sounds. At the same bit rates, AAC will usually sound better than MP3. At low bit rates, AAC is considerably better, at high bit rates, differences are smaller. AAC is widely supported.

The 44.100kHz sample rate is the standard rate for compact audio discs. The wav bitrate of 1411kbps is standard for uncompressed digital audio.
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Re: Need Info re Converting mp3 to WAV with iTunes

Postby George Tyndall » Sat Nov 06, 2010 6:05 pm

Bob wrote:AAC is a more recent format than MP3 and more flexible for content producers, but it's very similar to MP3. It's often said that AAC was designed to be MP3's successor. AAC also uses perceptual filtering (but improved over that used in MP3) and a lossy compression scheme. But, it has better handling of transients and high frequency sounds. At the same bit rates, AAC will usually sound better than MP3. At low bit rates, AAC is considerably better, at high bit rates, differences are smaller. AAC is widely supported.

The 44.100kHz sample rate is the standard rate for compact audio discs. The wav bitrate of 1411kbps is standard for uncompressed digital audio.


Bob and bobby:

So it's just my imagination that the WAV file sounds better?

Any explanation why WAV seemed to work better when using Fit Slides to Audio in PSE4?
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Re: Need Info re Converting mp3 to WAV with iTunes

Postby Bob » Sat Nov 06, 2010 6:35 pm

The quality of the MP3 decoder makes a difference, and not all decoders are equal. The decoder in iTunes may be doing something different from the decoder in your version of Premiere Elements. Also, the samples are stored differently in each format. The combination of quality of decoding and artifacts due to the conversion can make an audible difference. If that sounds better to you, great. You are definitely not getting recovered lost audio though.
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