[dblloyd]

I did a little searching on the forum and couldn't find any relevant info. Perhaps I'm searching for the wrong key words.




I'm interested in learning more about the different audio formats used for encoding music. Specifically, I have three questions for everybody:



1) Can you really tell a significant difference between a well encoded Mp3 or Ogg Vorbis music file and the corresponding CD or WAV file? If so, what kinds of things do these compressed formats not handle well?



2) Can you really tell a significant difference between a CD and DVD-audio or DTS? If so, how would you describe the difference?



3) I thought I understood why 44KHz was chosen for the sample rate of CDs: since we can only hear up to 22KHz, a 44KHz sample rate should be able to capture and reproduce all of the audible information that we can perceive. So I'm confused as to why DTS allows up to a 192KHz sample rate. What kind of improvement is really gained by this higher rate?



Thanks,

Dan

 

[brothermaynard]

I will offer an answer for only one of your questions. The quality of sound is directly related to the amp and speakers you have. On that note, for mp3's I do not touch anything under 160K and do not hesitate to go above.

 

[bitkahuna]

Quote:

Originally posted by dblloyd 1) Can you really tell a significant difference between a well encoded Mp3 or Ogg Vorbis music file and the corresponding CD or WAV file? If so, what kinds of things do these compressed formats not handle well?

If the MP3 has a lower bit rate, the dynamic range goes down and the sound gets less and less detailed. But I've converted all my CDs to 160kbps WMA files with Media Player and there's barely any difference to the original CDs.

Quote:

2) Can you really tell a significant difference between a CD and DVD-audio or DTS? If so, how would you describe the difference?

Well the obvious difference is DVD-Audio, Dolby Digital and DTS offer the benefits of discrete surround channels. I've come to prefer surround music over 2 channel (many disagree with me though) especially for concerts. However, like MP3, they're compressed formats, so the mastering, bit rates, and conversion can vary in quality. DVD-Audio doesn't incorporate video information (except stills usually) and so it can use all the bandwidth for audio meaning it has MUCH higher audio bit rates than anything else. SACD is similar but I don't know much about it. DVD-Audio and SACD though (today) require the player to decode the signal and output in 6 (or 2) channel analog format, so you have to do D/A in the player. However, the audio quality is still better than anything else.

Quote:

3) I thought I understood why 44KHz was chosen for the sample rate of CDs: since we can only hear up to 22KHz, a 44KHz sample rate should be able to capture and reproduce all of the audible information that we can perceive. So I'm confused as to why DTS allows up to a 192KHz sample rate. What kind of improvement is really gained by this higher rate?

Probably not much, but one BIG difference is the SIZE of the data samples. CD is a 16 bit sample, whereas DVD-Audio can have up to 24 bit samples, meaning bigger dynamic range and more detail.


But once you hear a decent surround DVD-Audio or DTS title, you might never want to listen to a CD on a home theater again. Be warned.

 

[Iostream]

As for the MP3/CD thing, I use an MP3 receiver to keep my entire CD library available for quick access. It is a decent format, and I encode everything at 160K. That said, I still do all of my critical listening on CD. Yes, MP3 is conveinient, but I find it lacks a little bit of the depth, even at 192k, and tends to lack some of the bass as well. For me, with nearly 1000 CDs, it is nice to be able to pull anything up, without having to find the CD, for background music, patio listening, parties, and while doing other things around the house, but if I am just sitting there to listen, I will always go get the CD. I have done several direct comparisons, and CD always sounds better. It is more of a difference on Jazz, Classical, and industrial, which tends to have more dynamic range, but it is still evident even on typical popular music.


Iostream

 

[bitkahuna]

Iostream - when you say 'MP3 receiver' - what's that? Is that like a Nomad? One thing to consider though with MP3 is what DACs are getting used for MP3 playback vs. CD.

 

[Gluegun]

If you encode MP3's at over 192 with the best encoders out there, it is pretty much impossible to tell the difference with the original .wav


You can even overlay the mp3 and the .wav, and subtract the difference between the mp3 and the wav, and be left with no audible or measurable difference....


....that is, if you know how to make a high quality mp3.

 

[dblloyd]

> ....that is, if you know how to make a high quality mp3.


What mp3 encoder do you use?



By the way, if you haven't tried Ogg Vorbis, you should take a look.

 

[Michael Sargent]

Quote:

Originally posted by bitkahuna I've come to prefer surround music over 2 channel (many disagree with me though) especially for concerts.

I find that fewer and fewer people are "stereo only" types once they have heard good multi-channel.

Quote:

Originally posted by bitkahuna However, like MP3, they're compressed formats, so the mastering, bit rates, and conversion can vary in quality. DVD-Audio doesn't incorporate video information (except stills usually) and so it can use all the bandwidth for audio meaning it has MUCH higher audio bit rates than anything else.

Just a point of clarification: DVD-Audio is not compressed. Specifically, Dolby Digital, DTS, and MP3 throw away part of the sound that they think you can't hear. DVD-Audio does not. There is a packing applied to reduce storage requirements, but that is a lossless packing and does not affect the sound. The recovered signal is 100% identical to the original signal, while the compressed formats are not.


Mike

 

[garion]

In regards to MP3:


One thing I have found that makes a huge difference is the sound card. For a while, I was using a Creative Labs SoundBlaster Live card in my MP3 machine, playing though my Diva's (via Onkyo reciever.).. I could alway pick out the MP3's playing at 128bit (encoded via LAME, not the crappy Xing one).


Eventually, I needed the SoundBlaster for another machine, and i pulled out an older, but high quality for its time, Gravis UltraSound MAX (a full length ISA card, damn that thing is huge).. And now I find it difficult to tell the difference between the CD's and 128bit MP3's.. The only thing that changed was the sound card.

 

[Iostream]

The MP3 receiver I was talking about is a Turtle Beach Audiotron. It is a neat receiver, no internal storage, just plug it into your netowkr, and it will search for MP3, WMA, or wav on any network shares. one warning, it's DACs are not very good, luckily, you can connect it digital, it is just a decoder and uses my receiver's DACs, same as my CD player.


Iostream

 

[Sean Parque]

1. I've never heard it, but Gluegun is pretty adamant about his encoding schemes. I believe him ...but I'm going to have to go get Lame and give it a try...


2. What everyone else said After listening to DVD-A, I find regular CDs sound compressed. That's the best way I can describe it. The dynamic range and clairity on DVD-A is pretty amazing if you've never heard it. I believe the highest bitrate for DTS is 1.5Mb/sec. DVD-A uses MLP or Meridan Lossless Packing and is 9Mb/sec which is the max that todays DSPs can handle.


3. Someone please jump in and correct me if I'm wrong here....


44KHz is a sample rate. I think the "Hz" confuses ppl. Heck, the electricity in a home in the USA is 50-60Hz and it has nothing to do with audio


bitkahuna was right, the word length or sample size is a big deal. When you take larger sample sizes and do this 96 or 192,000 times per second versus 44,000, you will easliy hear the difference. As has been mentioned, CD etc throw away info.

 

[bitkahuna]

Quote:

Originally posted by Iostream The MP3 receiver I was talking about is a Turtle Beach Audiotron. It is a neat receiver, no internal storage, just plug it into your netowkr, and it will search for MP3, WMA, or wav on any network shares. one warning, it's DACs are not very good, luckily, you can connect it digital, it is just a decoder and uses my receiver's DACs, same as my CD player.

Thanks - so it must convert any recorded bit rate into 44.1KHz 16 bit then so the receiver can understand the digital stream???

 

[dblloyd]

Ok, so DVD-Audio allows for a 24-bit sample while CDs only allow for a 16-bit sample. Thus each DVD-Audio sample is of higher quality.


But I'm still confused as to why DVD-Audio allows a sample rate of up to 192kHz. Based on my understanding of the choice behind a 44kHz sample rate for CDs, it would make more sense to me to design DVD-Audio so that it used the extra space to allow something like a 64-bit sample, at a rate of 44kHz.


So my question really is, how much is enough? At what point does increasing the sample size and rate lead to zero audible improvement? I thought the argument behind the choice of 44kHz was that going above this sample rate leads to zero audible improvement.

 

[Iostream]

Yes, the Audiotron umcompresses the MP3 to wav pcm, then sends the PCM stream to the receiver which does the D/A conversion. It acts as the player on your computer, which sends the digital sound to your soundcard DACs in the same way. It does actually have its own DACs, but I prefer the ones on my receiver.


As a big Linux/Open Source proponent, I like Ogg Vorbis, but it is still lacking in appliance support. MP3 at this point is still the most convienient format around for universal support.

 

[Mal P]

Hi dblloyd,


The following articles should cleap up some of the issues:

http://www.mindprint.com/english/24info.htm
http://www.mindprint.com/english/96info.htm


(Thanks to the poster in aus.hi-fi)


Cheers,

Mal

 

[David Panko]

Hi dblloyd,


The sampling rate of 44.1kHz was chosen because it was the best that could be done with late-70's digital technology, NOT because it perfectly covered the audible band.


In the early days the only way to record digital audio was on video tape since early hard drives weren't up to the task and CD had yet to be invented. Early recorders used three samples per NTSC video line, and with 245 interlaced lines per field at 60Hz this corresponded to a sample rate of 44.1kHz. The choice had nothing to do with audio quality and everything to do with the limitations of technology at the time.


The rate of 44.1kHz is far from sufficient since it means all frequencies above 22kHz must be blocked but everything below passed. A "brickwall" filter this close to audible band creates artifacts by phase shifting higher frequencies and smearing transients. Higher sample rates help to push these problems to higher frequencies where they are no longer audible. SACD (DSD) takes this to the extreme by sampling at 2.8 MegaHz!


For example, here is a plot the impluse response of different digital systems:

http://www.merging.com/2002/images/dsdresponseneon.gif


Cheers,

Dave.

 

[Michael Sargent]

Quote:

Originally posted by David Panko SACD (DSD) takes this to the extreme by sampling at 2.8 MegaHz!

But that 2.8 MHz is a 1-bit sample. The 96 KHz and 192 KHz samples for DVD-Audio are 24-bit samples. That "equates" to 2.3 MHz and 4.6 MHz respectively. Now, we all know that DSD vs. PCM can not be compared soley on the basis of numbers, but the claim that DSD is better because 2.3 MHz is bigger than 192 KHz is misleading.


Mike

 

[kaanage]

Yes. The advertising for SACD is incredibly misleading. They ignore the number of 1 bit DSD samples needs to be divided by the resolution of the recording before a meaningful comparision with PCM can be made.


Does anyone know what the resolution of SACD is?