MD, or MP3?

[Tate]

There should be a section here dedicated solely on lossy queries

Anyway, I'm not sure about a show I have. No lineage known, but it's an audience recording from 2003. I'm not sure though if it's MD cause the height of those flames (whatever you call them..) seems low to me. They end in a straight line at 13K, usually, the MD recordings I've come across end at around 16K. Could this be a MD recording, or maybe MD --> MP3?

Pics included. Thanks.

[ssamadhi97]

yikes. whatever it may be, it looks rather evil. I'd guess mp3 or mdlp (then again I don't really know what mdlp looks like), but I'm really not sure.

Either way this must sound pretty horrible.

[Five]

It's lossy and low-quality for sure. Doesn't really look like mp3 encoding to me. might be mdlp, not sure. I'll have to get some mdlp samples from somewhere. IMO mdlp should really only be used for recording voice journals and the like.

[Five]

Originally Posted by Tate

There should be a section here dedicated solely on lossy queries

We'll most probably have a new subforum for this in a week or two.

[Tate]

I never heard of mdlp The sound quality of the concert is not bad actually, it's distant but it sounds OK. Thanks for the help guys.

[Five]

mdlp = MiniDisc LongPlay (low quality setting)

in case anybody's wondering!

[robkismet]

I've been meaning to make some kind of reference guide of MD (incl LP) and mp3 spectrums using white noise samples for months. Is this worth my hassle once my exams are out of the way in a couple of weeks? Did a rough selection a while back but I need to sort it all out into a presentable form.

[symon]

Originally Posted by Five

mdlp = MiniDisc LongPlay (low quality setting)

in case anybody's wondering!

I have an MDLP recording (from the days when I didn't know any better!)
I haven't transferred it to PC yet - but I'll try and provide some examples when I do.

[Five]

Thanks guys, that would indeed be very helpful!

Rob, I would love it if you put together that guide, if you need any help please let me know.

Symon: when you transfer it to your HD perhaps you could send me a pm and perhaps I could get a hold of it via yousendit or whatever. thanks!

[farmstar]

I for one would love to see a comprensive spectral study. I have reieved some definately lossless shows that i cannot place, the spectral image and MD lineage solves a couple perhaps. It would be neat to see the LP spectral view.

[robkismet]

Originally Posted by Five

Rob, I would love it if you put together that guide, if you need any help please let me know.

Cool, hopefully I'll get that done in a couple of weeks (or more like tomorrow as part of the daily procrastination routine!). From the quick notes I still happen to have here, this sample with a cut at 13ish kHz is definitely not LP2 (132kbps). Could be LP4 (64kbps Joint Stereo) but looks more like 128kbps mp3 to me.

[Tate]

A reference guide sounds superb. Thanks, it will be very useful for all.

[ssamadhi97]

Originally Posted by robkismet

I've been meaning to make some kind of reference guide of MD (incl LP) and mp3 spectrums using white noise samples for months. Is this worth my hassle [..]?

White noise samples? That's not worth your time at all and has little use really. I mean, how many of us do spend their time on listening to white noise?

Seriously though, the specific fingerprints of lossy audio encoders are a direct result of the different ways their respective psychoacoustic models react to various properties of the input audio signal to exploit weaknesses in human hearing. White noise is only one very specific kind of input signal, which is why a reference guide based on it would be of little use indeed.

For example the changing lowpass you can observe on many lossy recordings is there because of the changing spectral energy distribution - and in some cases even the absolute amount of energy - in the input signal. Encoders can be distinguished to some extent by the lowpass they pick when encoding a signal of a certain distribution. When encoding white noise you only take one special case into account (namely uniform distribution)

Another example where encoders behave differently would be transients - some encoders (mp3, aac) switch between different block sizes to increase coding efficiency for tonal (long blocks) and transient (short blocks) material, while others ("old-fashioned" short-play md for example) use a fixed block size in all cases. Again, on white noise encoders will not exhibit any of this behaviour.


In short, you'd be better off using some snippets of real music instead.

Best you'd pick a bunch of clips that cover as much ground as possible wrt encoder behaviour on different signal types (ideally clips that cover tonal, transient and noise signals and different energy distributions all at once)

[robkismet]

I'd thought about this too and was unsure so thanks for your far more knowledgable advice. I was leaning towards doing sets with white noise, studio music, and also some less-than-stellar live recordings - should be interesting to see the differences too.