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cobb2 View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 04:37
Yes, but the bitrate still controls how much information in these frames is retained. That's why further on in this chapter a simple sine wave is shown displaying how a 64kbs retains less information than a 128kbs sample. I guess mine is a very basic view of the process- I deal with this with my Information Processes and Technology students (final year of high school) and they don't have to know the process in great detail. I basically just tell them that noises we can't hear are removed and show how the sampling rate works- using the sine wave example.
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Direct Link To This Post Posted: July 04 2009 at 04:46
Originally posted by cobb2 cobb2 wrote:

Sampling rate is just simply taking a snapshot of the frequencies at a given interval. CD usually lies somewhere between 2000 - 3000 snapshots per second. MP3 is whatever you set it up to sample at. 320 would resample the original wav at 320 snapshots per second- lossing 90% of the frequency data. This is gone forever, hence the lossy format. The magic occurs in the mp3 codec algorithms which attempt to fudge the missing information. The lower the mp3 sample rate the more impossible it is to fudge this. Hence a 64kbs is perfect for web download speed but quite atrocious to listen to. 

addition: if you then burn the 320kbs back to cd the algoritms in the burning software will resample it back to the higher wav sample rate, but now there are just straight lines between the original 320 rate and the new 3000 rate.
CD sample rates are 44,100 snapshots per second, not 2000-3000. Sampling an audio signal at 3000 samples per second would result in an audio bandwidth of 1.5Khz - which is about half that of an analogue landline telephone system and no where near good enough for music. The lost data in lossy systems is far to complex to describe in simple terms, but essentially the information that is lost is data that the human ear cannot hear because it is masked by more dominant sounds in the music. Mp3 codecs do not fudge the missing information - once removed it stays removed.
 
 
My error was confusing bit-rate and data-rate -
 
bit-rate = speed of the digital data stream in bits
data-rate = speed of the digital data stream in words (number of bits per sample x 2 for a stereo signal)
sample-rate = the speed in which the analogue signal is sampled
 
in uncompressed data the data rate is the sampling rate, the bit rate is 32 times greater than that (44,100 x 16 x 2 = 1,411,200);
 
in lossy systems the data-rate is not the sample-rate so are not related since (as Mike pointed out) the compression is done after sampling at 44,100 times a second - the resulting bit-rate of 128,000 bits per second is the compression from 1,411,200 bits per second - the original sampling rate remains unchanged.
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Mr ProgFreak View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 04:52
Originally posted by cobb2 cobb2 wrote:

Yes, but the bitrate still controls how much information in these frames is retained. That's why further on in this chapter a simple sine wave is shown displaying how a 64kbs retains less information than a 128kbs sample. I guess mine is a very basic view of the process- I deal with this with my Information Processes and Technology students (final year of high school) and they don't have to know the process in great detail. I basically just tell them that noises we can't hear are removed and show how the sampling rate works- using the sine wave example.


You mean image 2-3 on this page:

http://oreilly.com/catalog/mp3/chapter/ch02.html

That image is actually not correct. It shows the effects of quantisation at different sample rates, which - as Dean also said - are not to be confused with bit rates of MP3 streams.

The internet ... sometimes even O'Reilly can be wrong.LOL

EDIT: They're actually clarifying the difference later on ("Bitrates vs. samplerates") so they're not actually wrong, but merely inconsistent.


Edited by Mr ProgFreak - July 04 2009 at 04:57
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Dean View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 04:59
^ Yep - that's the page that mislead me Embarrassed 
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cobb2 View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 05:08
You guys know far more about this than I do Wink

The sampling rate I mentioned was bringing up the properties on a wav  audio file in windows. The details always show a bitrate. This is what is misleading me?
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cobb2 View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 05:42
It's alright, I have figured it out. Because MP3 (read MPEG) was made especially for the web this is the streaming rate across a network, so on a wav file, windows is just reporting the stream rate.

addition: although it still makes sense that the lower the kbs, the less samples there must be within the streaming frames.


Edited by cobb2 - July 04 2009 at 05:48
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Mr ProgFreak View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 06:01
For a typical 16bit/44.1khz WAV file the bitrate is 1411kbps, and that's what Windows will display to you. The important thing is that an MP3 file at for example 256kbps is not just a downsampled version of the original 1411kbps WAV file. The reduction in size is achieved primarily by looking at the frequency distribution of the signal and leaving out those parts that the human ear/brain can't perceive because they're masked out by other parts of the signal. Of course there are limits to this method of reducing size ... whether it's successful depends on many factors, most importantly the complexity of the signal and the resulting bitrate. If you encode a file at 128kbps, for most signals too many parts will have to be removed in order to accommodate the small file size. 128kbps is less than 10% of the original bitrate. If you encode at 256kbps (about 18%), you usually won't be able to hear a difference, or in other words: The mp3 encoder operates in a range that allows it to only remove parts of the signal that we can't hear, while still achieving the desired bitrate/file size.

I think this is the real problem: Some people simply refuse to believe that if you remove 82% of the original, the result can still sound exactly like the original (judged by human ears).

Take into account though that even when you apply only lossless compression, most tracks can be reduced to about half their original size. Or let's say 60%, to be on the safe side. So adding the lossy compression to the equation actually only adds an additional ~ 40% of compression. You can also take into account that today tracks are usually encoded using VBR (variable bitrate). This means that for each frame the mp3 encoder can analyze it and decide - depending on the complexity - which bitrate to use. The encoder can also select bitrates for left/right channels separately. In a nutshell: There are many ways the mp3 encoder can use to optimize the compression rate.

The bottom line for me: I have yet to hear a properly ripped ~256kbit MP3 that I could tell apart from the CD. I haven't done any real double blind tests, but I *never* found myself listening to such MP3 files and thinking "that sounds distorted/harsh/hollow, let's put in the CD".
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cobb2 View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 06:17
Originally posted by Mr ProgFreak Mr ProgFreak wrote:


I think this is the real problem: Some people simply refuse to believe that if you remove 82% of the original, the result can still sound exactly like the original (judged by human ears).

I think this line may sum up the audiophile problem with MP3. They know audio data is missing and may be pychosematic (bad spelling)  to what they are hearing- it can't be as good can it? therefore it isn't
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Mr ProgFreak View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 06:26
^ exactly. Personally, I don't ever think about that when I listen to music. A few years ago when I started to rip all my 1000+ albums as MP3, I was concerned ... but whenever I listened to the tracks - especially those that I had listened to on CD countless times over the years and knew in and out - I found no difference to the originals, and that really encouraged me to accept MP3.Smile 
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Dean View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 07:18
Originally posted by cobb2 cobb2 wrote:

Originally posted by Mr ProgFreak Mr ProgFreak wrote:


I think this is the real problem: Some people simply refuse to believe that if you remove 82% of the original, the result can still sound exactly like the original (judged by human ears).

I think this line may sum up the audiophile problem with MP3. They know audio data is missing and may be pychosematic (bad spelling)  to what they are hearing- it can't be as good can it? therefore it isn't
Compared to an analogue recording there is missing information in all digital data, including pure WAV files and  lossless compression methods. Compared to a live concert hall performance there is missing information in an analogue recording. Neither analogue nor digital is capable of reproducing the whole frequency spectrum or full dynamic range of a live situation. (even if that "live" situation is a recording studio).
 
The goal of Audiophile is two fold - a) to minimise the effects of those losses, and (more importantly) b) not to add any more extraneous information into the system.
 
A case in point (as mentioned by Oliver Stoned some time back) is the iPod - it is not an audiophile system, while the Wolfson audio DAC is at medium audiophile standard, the analogue circuitry between the DAC and the headphone socket is not. Audiophiles can have their iPods modified to bypass that analogue circtuitry, (http://www.redwineaudio.com/iMod.html), but they still will prefer to play lossless over mp3.
 
From a purity perspective bad mp3's remove information and add unwanted artifacts - higher bit-rate mp3s combined with higher sampling rates minimise both but at a price (file size). It is becoming evident that 256Kbps mp3 is indistinguishable from Red Book standard CD files for most people but anyone who is "unhappy" with CDs is not going to be "happy" with mp3 either.
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Mr ProgFreak View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 09:54
^ No doubt, some people will invest a lot of money into such esoteric devices.I never would. Today even your average low cost computer mainboard contains high quality DAC circuitry. Unacceptable by most audiophiles, I know. But again I trust my ears.Smile

Think about it: DAC circuits have been around for 30 years. Today computers are much faster, and more importantly: Manufacturing processes have been optimized. *Maybe* in the late 80s/early 90s it would have made sense to buy a $4000 CD player, but today? Come on.
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Direct Link To This Post Posted: July 04 2009 at 10:23
A modern sigma-delta DAC semiconductor costs around $0.10 to make and wipes the floor with the DACs from 30 years ago, but it is the associated circuitry around it that elevates it from adequate to hi-fi and then finally to audiophile. With all the best intentions in the world, a PC motherboard, chassis, power-supply and cooling system is not designed to be an hi-fi environment. A DAC on a motherboard not can be hi-fi and a high-quality soundcard may have impressive specifications, and coupled to some good quality speakers may sound very good, but it will never be audiophile since it is impossible to isolate the digital systems from the audio path - even on the soundcard you cannot get away from the PCI bus and all the associated rf radiation that emanates from the edges of the digital signals.
 
 
/edit - added the word "not" Embarrassed


Edited by Dean - July 04 2009 at 11:10
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Mr ProgFreak View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 10:29
I have an ASUS P5N-E SLI motherboard. When I first got this new computer I also used my Creative X-Fi soundcard, but I soon got rid of it because of driver problems (I use Vista 64bit).

Ever since I've been using the onboard Realtek hi-def sound card ... and I'm very happy with it. There is absolutely no audible interference from any component of the computer ... IMO it is simply an esoteric belief of many audiophiles that they have to protected their equipment from each other all the time ... every gadget needs its own power supply, the power supply needs power filters, the speaker cables need active shielding etc..

Come on people ... trust your ears!
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Direct Link To This Post Posted: July 04 2009 at 11:11
^ If you are happy, be happy. Big smile
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Mr ProgFreak View Drop Down
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Direct Link To This Post Posted: July 04 2009 at 11:28
^ I really am. Just finished listening to this fine album on my computer:

http://www.emusic.com/album/Kotebel-Ouroboros-MP3-Download/11447196.html

Heavily recommended to ... anyone really, I cannot imagine any Prog fan not liking it. And it surely put my Logitech speakers to the limit.Big smile
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Direct Link To This Post Posted: July 04 2009 at 15:51
I don't know much about the actual tech details between Mp3 and Wav files, but i do notice that ambient sounds feel like they have a slight bit more range, and are more prominent and pristine when comparing a CD vs MP3 of the same music. Of course, if you were listening to some pop song you probably could hardly notice the difference, but listening to music like Isis or GYBE, the difference feels quite obvious to me. 
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Direct Link To This Post Posted: July 04 2009 at 15:55
I purchased Wavering Radiant both on vinyl (excellent gatefold cover!) and as MP3 from eMusic.com:

http://www.emusic.com/album/Isis-Wavering-Radiant-MP3-Download/11412845.html

Maybe I'll get around to conducting a little experiment tomorrow: First I'll listen to the album on vinyl on my hi-fi, then I'll listen to the mp3s on my computer. I'll let you know if I hear a difference!
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Direct Link To This Post Posted: July 06 2009 at 00:32
So, considering that we're on the subject of audiophilia, my longtime headphones have finally betrayed me; anyone have some phones they're especially proud of or feel like making a special recommendation?




Originally posted by Mr ProgFreak Mr ProgFreak wrote:

^ I really am. Just finished listening to this fine album on my computer:

http://www.emusic.com/album/Kotebel-Ouroboros-MP3-Download/11447196.html

Heavily recommended to ... anyone really, I cannot imagine any Prog fan not liking it.


Just got around to checking this out, super nice tunes; thanks Big smile




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Direct Link To This Post Posted: August 06 2009 at 13:27
[QUOTE=Dominic]So, considering that we're on the subject of audiophilia, my longtime headphones have finally betrayed me; anyone have some phones they're especially proud of or feel like making a special recommendation?


Sennheiser 650. Trust me. :)


Edited by Rottenhat - August 06 2009 at 13:30
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Direct Link To This Post Posted: August 06 2009 at 14:03
Originally posted by Mr ProgFreak Mr ProgFreak wrote:

^ exactly. Personally, I don't ever think about that when I listen to music. A few years ago when I started to rip all my 1000+ albums as MP3, I was concerned ... but whenever I listened to the tracks - especially those that I had listened to on CD countless times over the years and knew in and out - I found no difference to the originals, and that really encouraged me to accept MP3.Smile 

I have tried to tell the difference between a cd, a 320 kbps mp3, and a 256 kbps mp3. At a reasonable listening level I noticed no difference between any of them. I have even been thinking about reripping my cds to 192 kbps. I have everything from 128 to 356 on my mp3 player, and I never notice which is which. The only time I notice bad quality sound is when the recording itself is bad quality.
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