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Topic: Wav to ALAC, Quality loss or newbie question? (Read 4599 times) previous topic - next topic
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Wav to ALAC, Quality loss or newbie question?

Hello all, I just joined this forum (although I've been reading it for some time) because I can't find the answer to this question anywhere, maybe it's just me being a newbie but can't can't know for sure, so please answer.

I played a WAV file into Itunes and of course it did, then I decided to convert it to ALAC, so I right clicked it and selected "Make an Apple Lossless version". After it was imported, there was a KBPS decrease from 1411 to 1040.

Acording to my understanding, that should mean quality loss, maybe I'm wrong since this big a bug could not have gone unreported for so long. So...any explanation on the meaning of this? Thanks in advance.

Wav to ALAC, Quality loss or newbie question?

Reply #2 –
The entire point of lossless audio compression is to maintain quality while reducing bitrate (= file size).

Who was it that mentioned having an official FAQ? It looks more necessary by the day.

Wav to ALAC, Quality loss or newbie question?

Reply #3 –
Oh, I thought bitrate was = to quality

What numerical factor is what determines quality then?

By the way, yes I did search for a FAQ, and the only thing I found was one that had all the questions pre-answered. A more forum-like one should defintely be made.

Wav to ALAC, Quality loss or newbie question?

Reply #4 –
Quote from: Wolf Ears on
Oh, I thought bitrate was = to quality
Not for lossless. And not necessarily for lossy.

Quote
What numerical factor is what determines quality then?
Are we to assume that you are referring to lossy audio compression, since lossless is loss-less?

If so, rather than a number, why not use your ears? That is, after all, the (main) point of lossy audio compression: to shrink the file, and more so than lossless methods can, without creating any noticeable decline in quality or other audible difference. You can use bitrates, or the settings used to invoke them, as a guide to the probability of transparency, but audibility is the ultimate adjudicator.

You may find related articles on our Knowledgebase or on Wikipedia, etc. informative.
 

Wav to ALAC, Quality loss or newbie question?

Reply #5 –
OK, thanks dude, but you need not be that patronizing when answering a question. I know Lossless is Loss-less, but who know's if there could be a bug in the lastest version of itunes or whatever, you're not going to atract many new guy's into the forum that way, to be a expert it's necessary to start as a begginer.

Wav to ALAC, Quality loss or newbie question?

Reply #6 –
db1989, why bother? Marc posted best answer, and it seems you only offended this newbie which your kindness instead attract him

Wav to ALAC, Quality loss or newbie question?

Reply #7 –
I don’t see how I’m being patronising. I offered some information and suggested some sources where you could find more. If my pointing out the etymology of the word lossless is unnecessary in your case, you’ll excuse me on behalf of the number of new users who don’t seem to grasp the concept.

Again, I didn’t intend to patronise. Hopefully the forum and Knowledgebase can be of use in your understanding of subjects such as these.

I just noticed your edit:
Quote from: Wolf Ears on
By the way, yes I did search for a FAQ, and the only thing I found was one that had all the questions pre-answered. A more forum-like one should defintely be made.
A pre-answered FAQ was what I meant—rather than a question topic, if that’s what you mean—but one that is up-to-date and also includes some rudimentary points about fundamental concepts and questions such as yours (which is not to imply that they’re the worst we get!).

Wav to ALAC, Quality loss or newbie question?

Reply #8 –
Quote from: Wolf Ears on
Oh, I thought bitrate was = to quality


bitrate = bit rate = amount of bits during a defined period of time

bitrate in audio/video codecs = 8 times the number of bytes (8bits = 1 byte) that a content (audio, video, whatever) needs to be stored for the duration of a second.

bitrate of an audio CD* = 1441 kbps (kilobits per second) = 44.1Khz * 2 channels (stereo) * 16bits . (16 bits = 2 bytes).


compression = reduction of the size of something.
codec compression = reduction of the bitrate requirements for a content (audio, video, whatever).

bitrate for a lossless audio file =  the amount of bits needed for that content, which, because it has been compressed, is smaller than the original.



The bitrate for a lossless codec can only be reduced by applying more complex algorithms (more time to encode and decode), because all information has to be kept.

The bitrate for a lossy codec can be reduced by reducing the quality, because it can discard information. (I.e. it does what it is designed to do)


Maybe the answer is a bit technical, but understanding these two correctly avoids the confusion completely.




* Ok. strictly speaking, the bitrate of the PCM data of an audio CD.

Wav to ALAC, Quality loss or newbie question?

Reply #9 –
Quote from: db1989 on
Again, I didn’t intend to patronise. Hopefully the forum and Knowledgebase can be of use in your understanding of subjects such as these.


Ok, I misread you then, sorry. And I know that it doesn't imply it's the worst you get  Thanks for answering.

Quote from: [JAZ] on

bitrate = bit rate = amount of bits during a defined period of time


Yes, but I thought it would be equal to quality since the more bits you have per-instant should mean a richer sound. So then, what is the extra bulk that is deleted from a wav file in a lossless compresion, is it just the leftover from a pre-existing format of the basic making of a CD? Yet this file was a FLAC that I turned into WAV using FLAC frontend, and then turned itno ALAC, what's the rest of it.

I know about alrhythms and bytes and stuff, so don't worry.

Wav to ALAC, Quality loss or newbie question?

Reply #10 –
Simply, the algorithms that were used to compress the audio data are run in reverse, regenerating PCM audio at the original bitrate (e.g. 1411 kbps) to be output to your audio hardware. The same thing would happen when a lossy file was decompressed. I suppose this distinction between compressed and uncompressed bitrate is an important one to note in this case.

Wav to ALAC, Quality loss or newbie question?

Reply #11 –
Quote
So then, what is the extra bulk that is deleted from a wav file in a lossless compresion

It is lossless - nothing is deleted. Forget audio, think of text. The encoder reads a large file every time it see the word THE it changes it to 1. The 1's take less space than THE. The file is smaller - nothing is deleted.  The decoder sees the 1's and changes back to THE. Nothing was deleted.

Wav to ALAC, Quality loss or newbie question?

Reply #12 –
Quote from: tpijag on
Quote
So then, what is the extra bulk that is deleted from a wav file in a lossless compresion

It is lossless - nothing is deleted. Forget audio, think of text. The encoder reads a large file every time it see the word THE it changes it to 1. The 1's take less space than THE. The file is smaller - nothing is deleted.  The decoder sees the 1's and changes back to THE. Nothing was deleted.


AWESOME explanation, thank you!

Quote from: db1989 on
The same thing would happen when a lossy file was decompressed. I suppose this distinction between compressed and uncompressed bitrate is an important one to note in this case.


And how is it that a lossy format can recover? I mean, the program that does it has no knowledge whatsoever of the original file, how does it do it (in fact, I didn't even know it was possible), I guess it requires that it's the same program that compressed it and that it retains some memory of the file.

I know I'm asking loads of questions, but I'm a music composition student, so I must know!

Wav to ALAC, Quality loss or newbie question?

Reply #13 –
There is a wiki here, Wikipedia and web. Concepts are addressed pretty damn well in documentation everywhere. Questions are fine, but please remember everyone is volunteering their time. Would be considered thoughtful to do some basic reading.

Wav to ALAC, Quality loss or newbie question?

Reply #14 –
Quote from: Wolf Ears on
And how is it that a lossy format can recover? I mean, the program that does it has no knowledge whatsoever of the original file, how does it do it (in fact, I didn't even know it was possible), I guess it requires that it's the same program that compressed it and that it retains some memory of the file.
The lossy compressed format can be decompressed - it is when it is played. Decompression results in the same bitrate as the original (generally.... lame converts to 32kHz for some quality settings). What is not recovered on decompression of lossy is the information that was discarded during lossy encoding.

In short, decompressed lossy may have the same bitrate as the original but it is lossy nonetheless.
lossyWAV -q X -a 4 -s h -A --feedback 2 --limit 15848 --scale 0.5 | FLAC -5 -e -p -b 512 -P=4096 -S- (having set foobar to output 24-bit PCM; scaling by 0.5 gives the ANS headroom to work)

Wav to ALAC, Quality loss or newbie question?

Reply #15 –
Oh, now I realize I knew the answer to that....but anyway, thanks to all!