[Frank_Zuccarini]

Hi.

I know that CD quality is designated as 44.1 kHz, which is 44,100 Hz, which is 44,100 cycles/second.

I also know that MP3 files are typically produced at sampling rates of 128 - 320 kbps, which is kilo bits/second, which is thousands of bits/second.

What I don't know is, how does 320 kbps (for instance) relate to 44.1 kHz. In other words, if I was to produce a MP3 file that was the SAME quality as the original source CD (I know that there is no reason to do this, but I'm just saying), how many kbps would that MP3 file be?

I'm just trying to understand how the two indices of music quality are related, if they are at all. 44.1kHz = ? kpbs

Any layman's explaination would be appreciated.

Thanks.................Frank

 

[ILikeMusic]

There is no relationship between the sample rate of an uncompressed PCM file (such as on a CD) and the bitrate of a compressed track. They both do have an impact on audio quality, but technically they are two very different things and there is no exact equivalence possible.

An MP3 file will never be exactly the same as an uncompressed source as the encoding process necessarily discards some data. The intent of a lossy compressed file is not to provide an exact reproduction of the original in terms of bits, but rather relies on psychoacoustic principles to reduce the filesize while remaining audibly identical to the human ear (even though it is not really identical, and cannot be used to reconstruct the original source file.) The more bits the encoder has to work with the better it will be able to accomplish audible transparency, but again this bitrate figure is not related to the sample rate of the source file.

The details here can be kind of involved (more than can easily be explained in a single response) and I'd recommend searching around on the Internet for some tutorials (Wikipedia, etc.) on the subject. There are several good ones which will get you stared in the right direction.

 

[Frank_Zuccarini]

Thanks for your help, I appreciate it.

Actually, I did do a number of Head-Fi and general net searches before posting my question. As you point out, there is a lot of information, including in Wikipedia. However, I did not grasp the fundamental concepts that you have now conveyed to me.

Bottom line is, I CANNOT compare a CD's 44.1kHz to any compression technique's kpbs sampling rate. Thank-you for explaining that for me.

Regards..............Frank

 

[sejarzo]

You also might find it interesting that even the lossless encoding algorithm used by FLAC ends up with different bit rates for 44.1k source material.

Classical music with lots of softer passages ends up in the 550 to 600 kbps range, while hot mastered pop/rock is often in 900 to 1050 kbps range. For comparison, an uncompressed native 44.1k .wav file has a total bit rate of 1411 kbps.

There are no psychoacoustics considerations involved with that, it's simply that the louder the music, the more bits are required to represent its amplitude--and the data can't be packed as tightly as a result.

 

[Frank_Zuccarini]

Ahhhhh..........an uncompressed native 44.1k .wav file has a total bit rate of 1411 kbps.

I still don't really understand it, but that seems to be the comparison that I was looking for.

Thanks for the help.

Frank

 

[nick_charles]

Quote:

Originally Posted by Frank_Zuccarini /img/forum/go_quote.gif Ahhhhh..........an uncompressed native 44.1k .wav file has a total bit rate of 1411 kbps. I still don't really understand it, but that seems to be the comparison that I was looking for. Thanks for the help. Frank

It goes like this

Stereo is 2 channels
each channel has 44,100 samples per second
there are 16 bits per sample

2 x 44,100 x 16 bits = 1411200 bits per second

 

[doomlordis]

Ok laymens terms , imagine a sound wave , bends up and down depending on the sound, looks a bit like hills. That is analogue.
Now imagine you wanted to recreate that but had a finite number of points where you could measure it (placing dots along the line of the hills) , the sample rate is the number of dots per second of sound you use.
Now there is a theorem (Nyquist) kicking about that dictates that in order to get a proper reproduction of the hills you need to have twice as many dots as the maximum frequency it contains (human ear can hear 20 Hz to 20 kHz roughly) so you need at least 40khz to catch all of that.
That is why the sample rate of cd is 44.1 KHz.

Hope this helps.

MP3s have generally have the same sample rate as CD , they just try to discard data and cut the frequency range (20hz - 20khz becomes 20hz - 16khz at 128kbps mp3) that isn't heard , leading to smaller files , i.e 320kbps mp3 against 1411kbps cd.

94% of men can only hear up to 16khz by the age of 32.

 

[Frank_Zuccarini]

Now I know the answer AND I understand it. These last two responses have clinched it for me.

Thank-you, thank-you, thank-you.....................Frank