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Topic: Home-Brewed Spectral Analysis (Read 3715 times) previous topic - next topic
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Home-Brewed Spectral Analysis

Hi people! 

I've only recently started playing with LAME, and I'm currently using version 3.97 Beta 2 MMX.

A strange idea came to me regarding how to find the minimum required CBR bitrate to capture all of the necessary audio components in a music track.

Suppose that we first encode that track in VBR with minimum bitrate set to 32Kbps and maximum set to 320Kbps. We now view that file using the bitrate distribution chart in EncSpot, if we look to see the highest bitrate envoked, this must surely be the highest required CBR bitrate to capture the same signal. 

Another puzzler to me... If this CBR file is now losslessly compressed with MP3Packer, do we still have the same file? Is more detail preserved? Could this method be a cure to the artifacting that some people seem to hear in some VBR files?

One last thing that puzzles me regarding my 320Kbps VBR files (which sound stunning, by the way!  ).
If I invoke the switch that disables band 21 and knocks out everything above 16KHz (by selecting -V3, for example), then the usage of 320Kbps frames doesn't reduce as far as I can tell. Does this infer that we need more than 320Kbps to capture a signal with a 16KHz cut-off?

Interestingly, the encodes I've made at -V3 sound cleaner to my ears than those made at -V2, and not much sneaks past a pair of Sennheiser cans without being painfully noticed. 

Apologies for not sticking with the presets provided, but I have an inquisitive mind... D'oh!

Please excuse me if the questions seem a bit noobish, but... err, I'm a noob, and MP3 and LAME have me pretty excited right now!

Cheers, Slipstreem. 

Home-Brewed Spectral Analysis

Reply #1 –
Sorry but your post is confusing and violates T.O.S. #8:
Quote from: Slipstreem on
Interestingly, the encodes I've made at -V3 sound cleaner to my ears than those made at -V2, and not much sneaks past a pair of Sennheiser cans without being painfully noticed. 


J.M.

Home-Brewed Spectral Analysis

Reply #2 –
Quote from: Slipstreem on
Another puzzler to me... If this CBR file is now losslessly compressed with MP3Packer, do we still have the same file? Is more detail preserved? Could this method be a cure to the artifacting that some people seem to hear in some VBR files?

Lossless means just that: no loss in quality. MP3Packer just removes padding, bits that don't affect the decoded data. You could add the padding back in and get the original file back.

Quote from: Slipstreem on
One last thing that puzzles me regarding my 320Kbps VBR files (which sound stunning, by the way!  ).

Do you mean 320Kbps files that you've run through MP3Packer? (There's no such thing as 320Kbps VBR.)

Quote from: Slipstreem on
Interestingly, the encodes I've made at -V3 sound cleaner to my ears than those made at -V2, and not much sneaks past a pair of Sennheiser cans without being painfully noticed. 

Please read TOS #8. Have you ABXed either of these?

Home-Brewed Spectral Analysis

Reply #3 –
Hi 

Apologies for the violation. I did fear that I may be sailing a little close to TOS#8.

I was careful to state "...to my ears...", and hadn't realised that it would still count as a no-no.

And yes, I meant to say original LAME MP3 VBR file with max bitrate of 320Kbps.

My noobness betrays me. Sorry. 

Cheers, Slipstreem. 

Home-Brewed Spectral Analysis

Reply #4 –
Your assertions are highly dependent on vagaries of the internals of an encoder, and so have little meaning to them. Yes, you could take the maximum CBR bitrate for a VBR encode and call that "safe" for that encode, but you can't logically use that for any other encode, nor for any other encoder, or any other encoder setting. The 320kbps/sfb21 thing is probably an implementation artifact of either MP3 or LAME.

Home-Brewed Spectral Analysis

Reply #5 –
You say that 320Kbps MP3s sound stunning... Could you please perform a few ABX tests for us, and post the results?

Try with an album you know well, start by ABXing -V5 --vbr-new
If you succeed (p-val < 5%, let's say -- 8/9 works), then your assertion can be believed true for that bitrate.  Rinse and repeat, but I'm pretty sure you won't be able to reach -V3 --vbr-new.

Good luck,
Tristan.

Home-Brewed Spectral Analysis

Reply #6 –
Hi Tristan. 

Thanks for flaming me the least so far.

I seem to have come to the wrong place to share my newfound enthusiasm over the progress LAME is making. Am I the only happily contented person left on the planet?

As it is impossible for me to prove what's going on inside my head regarding sound processing, I can't give anyone else evidence that it sounds right to me. 

I will try a blind A/B comparison at some stage, but sitting here switching between the two sources manually, I'm not audibly aware of any change in quality either way.

My settings seem to work best for me as I don't personally hear this level of transparency with any of the presets. Maybe it's my choice of music that doesn't fit them.

Maybe my 41 year-old ears just don't cut the mustard anymore.   

Anyway. I like what I hear and I'm HAPPY!

Cheers, Slipstreem. 

Home-Brewed Spectral Analysis

Reply #7 –
You're in the right place to encourage the LAME developpers on their progess, slipstream.  If you really want to be on the bleeding edge of developpement, you can always find current LAME Alpha releases at Rarewares.  In any case, just try to make sure you have objective evidence before affirming things : site like hi-fi.org have claims that resemble yours, and are very ill seen here (the claims, not the site, necessarily -- I'll refer you to this post)
All in all, we wish you welcome to HydrogenAudio Forums, surely the greatest place to stay in touch on all the digital audio technologies, and in particular in audio compression.

I sincerely suggest you take the time to do a BLIND A/B test, also known as ABX tests.  You'll probably find, as many other users here did, that you have less good hearing than you might have thought.. Or simply less training to hear lossy artifacts.  You might want to do an easy test, by downloading samples from the last 128kbps listening test.  It is fairly simple to do, but is quite a blow to the ego ;-)

Here is a sample still available :
http://www.hydrogenaudio.org/forums/index....showtopic=40625

Have fun,
Tristan.

Home-Brewed Spectral Analysis

Reply #8 –
Thanks, Tristan. 

After having read that post you pointed me to, I can see your point entirely. 

Cheers, Slipstreem. 
 

Home-Brewed Spectral Analysis

Reply #9 –
Quote from: Slipstreem on
We now view that file using the bitrate distribution chart in EncSpot, if we look to see the highest bitrate envoked, this must surely be the highest required CBR bitrate to capture the same signal. 
I think it might be an okay estimate.  I think noise shaping has to be taken into consideration more with CBR than with VBR.

Quote
If I invoke the switch that disables band 21 and knocks out everything above 16KHz (by selecting -V3, for example), then the usage of 320Kbps frames doesn't reduce as far as I can tell. Does this infer that we need more than 320Kbps to capture a signal with a 16KHz cut-off?
-V3 through -V9 already have -Y set by default, so adding -Y when you are using one of those VBR modes won't change anything.  It will make a difference with -V0 - -V2.  Also, -Y does NOT "knock out everything above 16khz", it's more complicated than that IMHO
http://www.hydrogenaudio.org/forums/index....showtopic=37150
I think --lowpass 16 is more useful.

Quote
Interestingly, the encodes I've made at -V3 sound cleaner to my ears than those made at -V2, and not much sneaks past a pair of Sennheiser cans without being painfully noticed. 
That statement makes me call into question your hearing abilities  ...unless you are using some exotic settings, in which case, do share 

Quote
Apologies for not sticking with the presets provided, but I have an inquisitive mind... D'oh!
Welcome to the club
Vorbis-q0-lowpass99
lame3.93.1-q5-V9-k-nspsytune