### Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: more detail about compressing technology. (Read 2507 times)
0 Members and 1 Guest are viewing this topic.

## more detail about compressing technology.

##### 2003-03-05 03:25:48
I have looked around for information on how MP3 and others work but have only found basic descriptions and no hardcore detail. Can anybody point me to the deep inside structure of the technology? For instance i hear people saying that it is good to cut out low frequencies because that will save space. That totally goes against my logic because low frequencies have much less waves per time unit and so need much less samples and bits to define an accurate waveform. To me the highest frequency present at any given moment will determine the amount of bits required to have a clear sounding signal. People think it's logical that when the sound is less intense it should use less bits but i fail to see why. I think it should be the frequency and complexity of the waveform and not the amplitude. With .wavs i take it that they choose a sample rate [44khz] that is twice the frequency we hear up to, and so that will be able to cover that upper end and anything below it with increasing definition. In mp3 technology it seems that frequency is divided into bands. I fail to see how that will save space when you now have to have seperate bits for each band. I can understand cutting out highfrequency band or lowering the sample rate when there is no audible sound present up there(since higher freqs require more bits for time for a given definition), but how would it benefit to cut out antthing lower(when ther are only highs present) when it could just ride on the same bits as the higher definition high freqs? My ideal compression system would be to vary the sample rate according to the highest frequence present in that frame and then to use the ham coding, or whatever, to do lossless compression on the sample positions or values. I don't really understand the point in cutting out mids or lows or even dividing into discreet bands in the first place. Maybe the cutoff lowpass should be continuously variable and no bands? But i have more to understand about the details before i can come up with what will really work. What do you think??

## more detail about compressing technology.

##### Reply #1 – 2003-03-05 07:50:25
Quote
I have looked around for information on how MP3 and others work but have only found basic descriptions and no hardcore detail. Can anybody point me to the deep inside structure of the technology?

Follow the links in the "Books" section of http://www.audiocoding.com/wiki, e.g. the one about "Introduction to Digital Audio Coding and Standards". If you don't want to buy a book, you can also try to find answers in the papers mentioned there and in the "Simple Technical Information" or "In-Depth Technical Info" pages.
ZZee ya, Hans-Jürgen
BLUEZZ BASTARDZZ - "That lil' ol' ZZ Top cover band from Hamburg..."
INDIGO ROCKS - "Down home rockin' blues. Tasty as strudel."

## more detail about compressing technology.

##### Reply #2 – 2003-03-07 00:57:36
Thankx for the info. What are some books to look at? I couldn't find the books section.

## more detail about compressing technology.

##### Reply #3 – 2003-03-07 05:46:37
Quote
Thankx for the info. What are some books to look at? I couldn't find the books section.

Just scroll down this page, there are some links to click on... If you still can't find them, go directly to either the "Books and papers"  section of the MPEG homepage or the description of "Introduction to Digital Audio Coding and Standards".
ZZee ya, Hans-Jürgen
BLUEZZ BASTARDZZ - "That lil' ol' ZZ Top cover band from Hamburg..."
INDIGO ROCKS - "Down home rockin' blues. Tasty as strudel."

## more detail about compressing technology.

##### Reply #4 – 2003-03-09 12:10:36
that is one expensive book at \$125!