Axiom Home Page Forums General Discussion Home Theater MP3 vs Lossless Compression - the proof

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Didn't they do "Radar Love" or some other 70's arena rock anthem?

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And Twilight Zone!

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Hey, if CDex calls the LAME encoder, what's the difference between using that and using EAC? Is that a stupid question?

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One's even got the word Exact in it's name... it's gotta be good!

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Also, Neverhappy really likes the 320 bit coding, and the quality-preservationist in me buys that premise. Is there ANY advantage (besides saving some disk space) of using variable bit rate instead?

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VBR saves some space (for downloading off websites or what-have-you) as for not liking using VBR - you're already asking a codec to decide what you can and can't hear, might as well loosen the leash and let it decide to what extent you can and can't hear as well!

Bren R.

Thanks again, John. I appreciate your time and patience.

Aye, a lot of good information here.

To chip in regarding EAC vs CDex, they both do some pretty advanced things to minimize jitter, etc, but EAC has what is called "Secure Mode"* where it reads each part of a CD at least twice and compares the result-- if it doesn't get the same both times, it carefully reads that part over and over to get the correct result. If that fails, it'll tell you. I find it a bit slower than other rippers because of this, but it's worth the peace of mind to me. There are a few more features of EAC that I don't believe CDex has, but that's the major one.

*I'm almost sure that CDex doesn't do this, and I checked the webpage, but it's quite possible that I'm wrong.

Regarding VBR vs constant bitrate, I agree with NH that there's no quality gain from going VBR over just going 320k. However, for, say, a 192k file, VBR will be hugely better. Another way to look at the debate is "constant bitrate is variable quality, variable bitrate is constant quality". VBR got a bad reputation because of some early bugs in MP3 encoders and players, but all that's over now. It's good stuff, especially LAME's implimentation.

Reply to Bren following soon.

When setting up a VBR encoding, the bit-rate you choose is the guaranteed minimum, right? For example, if I set up an encoding session, pick a root bitrate of 192 and enable VBR, that means I'll have a guaranteed minimum bit-rate of 192 in all my songs, but the encoder will boost it higher as necessary to get a cleaner sound.

At first, I thought VBR meant the encoder could drop OR raise the bitrate.

"Exactly - part of the MP3 compression scheme they claim is that if a triangle is being struck at the same time as a bass drum, you'll never hear the triangle - but how does a computerized encoder know what's a triangle and what's a bass drum? I'm assuming that if there's a loud sound in a certain frequency band, that it ignores or uses less resolution in the other frequencies. It's hard to say. In the end, I was just showing what the differences were between the two. People can make their own decisions."

How the MP3 codec calculates masking is actually pretty cool-- imagine making a spectrum graph 75 times per second, finding the peaks, then drawing a diagonal line down both directions from each peak (the slope of the line depends on various and sundry things). Anything below the line is masked (this is the core of how masking works, though there's much more math behind it).

Depending on the harmonics and tuning of the bass drum and triangle, the triangle will probably be masked-- but the beauty of this method is that the encoder can just rely on this 'geometric' method and not know what's making the sounds.

"You speak of the Golden-Earred? "

Perhaps. The psychoacoustic model in LAME is wonderful, but psychoacoustic models aren't always one-size-fits-all.

RD

PMB, that really depends on the program.

Technically speaking, the VBR bit-rate you choose is supposed to be the guaranteed minimum; however, it's rather ambiguous whether some programs use standard VBR when you choose VBR, or a type of VBR called ABR ("average bitrate"), which would aim for an average bitrate centered on the bitrate you chose.

It's worth checking to see if your program makes a distinction between VBR and ABR.

By the way- a neat thing about VBR is that, when there's only absolute silence, the bitrate can drop down to 32k (even if you set a hard minimum). With 320k, you use 320k for silence, too.

RD

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Is there ANY advantage (besides saving some disk space) of using variable bit rate instead?


One potential issue (other than saving some disk space) could be the network bandwidth required to feed the mp3's from a PC to a remote digital video player. Now, if all of your components are hardwired, or you have a solid 802.11g network, I'm sure you'll be fine streaming whole uncompressed .wav files. If you have a marginial 802.11b network? Who knows?

I used 802.11b to stream my MP3's(256kbs no VBR) with no issues.....surf the web with my laptop at the same time too.

Ok, maybe I was worring about nothing. I checked around a little and it looks like a typical real world 802.11b connection running wireless encryption (as you should), will get at least 2Mbps (probably more). A 320kbps MP3 will only use about 1/6th of the connections throughput -- plenty of room left for surfing.

Now here's the confusing part to me. By my estimates, a fully uncompressed wav file is only around 170kbps? Huh? I must have made a mistake somewhere. Here are my assumptions:
A typical 20 minute CD uses about 1/3rd of a 600MB CD, therefore 20 minutes of wav files should be around 200MB. This yields around 204,800,000 bytes in 20 minutes. Or about 170,000 bps = 170kbs. That doesn't seem right, that would mean that a high quality MP3 is using almost twice the bandwidth of a raw wav file. There's obviously something I'm missing here.


Btw, here's a link that listed some "real world" wireless connection bandwidth info...
http://www.homenethelp.com/802.11b/index.asp

The mistake you are making is in units. You have to understand that 8 bits (binary digits) make up one byte (binary term). Redbook CD Audio at 44.1 kHz and with a resolution of 16 bits takes 176.375 KB/s (KBps or KiloByte / sec) or 1411 Kbps (Kb/s or Kilobit/sec) (which is significantly higher than a compressed MP3, even at 320 Kbps.)

As a side note: transfer rates for network connections are generally reported in base 10 instead of base 2 and are Kbps (not KB/s).