Mp3 or Not???

[RainDawg]

Five, I believe the issue with your spectral plot is that it only shows the activity where your cursor is currently placed. The first one, it may have been at the beginning of the file where nothing was happening yet. When you clicked in the middle of the display, presumably to a spot there there is more "music", it suddenly shows you a more interesting plot.

One of the weaknesses with the freq analysis in CEP is that it will only display for one sample at a time, so even if you select a large portion, it will only display the information for the sample where the cursor is actually located. AnalFreq will run a progressive analysis, and display either the current position, or an average of what it has scanned so far.

This is why lossy stuff is so much easier to spot with AnalFreq than with CEP. Since the high end content on an mp3 file is just random noise, taking the average of it over an long period of time is going to result in a perfectly flat line, whereas each instantaneous plot (as in the pics above) is going to have some activity present. It will also accentuate that steep dropoff as it takes the average, making FM vs. MP3 much easier to definitively state. FM and TV have, as you said, a nice smooth rolloff when you take the average over the whole file.

I'm just not a fan of CEPs freq analysis tool, as it doesn't seem to really be useful for spotting sources as much. The Spectral Analysis tool is great though.

[jcrab66]

Five, I got the same results as you as far as moving the cursor and getting a different wav display...

[Five]

jcrab66: that's great!

RainDawg: I think you may be right, it could be the first sample. We'll get to the bottom of it somehow. I think AnalFreq is great, too, I just don't like waiting so I usually only use it when I need to.

[RainDawg]

Well, that's the thing with AnalFreq, you do have to wait because it is going to scan the whole file. There is simply no way to do it on CEP...it's only going to display a single sample analysis at a time.

But with AnalFreq (I just love saying the name) you really don't need to scan the entire file. Usually about 10-20 seconds of the audio is all you need for the high end noise to average itself to zero and the rolloff becomes defined enough to tell whether it's lossy or FM.

[ffooky]

I'm surprised no one has mentioned Audacity. You get a maximum 23 second stretch to analyse and the rolloff is always very clearly defined.

[Five]

yes, let's talk more about Audacity...

I'm going to start playing around with the SA and seeing how well it works for our purposes.

I can't seem to find FA in there, can Audacity do this?

fooky, can you please expand on this bit about the 23 second stretch? I don't quite understand.

[ffooky]

Select a length of the waveform (up to 23.8 seconds in length..hence the stretch thing) and go to the View menu. Select Plot Spectrum and Bob's your uncle. I must say I find it the easiest FA to read, though the SA is merely sufficient. I haven't really tried any of the other progs apart from EAC but I find it picks noise reduction from MPEG encoding pretty well...the roll off with NR usually seems to have a stair step effect even though the SA looks like boxed standard lossy.

[Five]

ahh yes, I've got it now!

looks great! I'm going to use it for sure next time I'm doing an analysis and see how well it works.

now if I could just remember how to cut on sector boundaries using audacity

[Five]

well, what do you know.

the time is right now.

I just visited an announce thread on EZT. This is most certainly lossy, looks like VBR.

CEP SA, zoomed in and full track view:

[Five]

Here's SA using Audacity, zoomed in and fulltrack. I can't tell anything from these shots.

[Five]

Here's SA using EAC, zoomed in and fulltrack. You can see the telltale blocky lego spikes pretty well, especially on the closeup.

[Five]

Here's FA

1) using AnalFreq with default settings on the left channel. You can sort of see stairsteps in the highs.
2) using CEP set to FFT size 1024 to match AnalFreq's settings.
3) using CEP set to FFT size 512 (default)

[Five]

And finally the FA using Audacity. Audacity's FA seems to show the suspicious stairsteps the most clearly.

1) using FFT size 1024 to match AnalFreq's default
2) using FFT size 512 (audacity default)

[Five]

and here's the EAC FA, set to FFT sizes 512, 1024, and 65536 (max). Not much useful information in these shots.

[Five]

so these screenshots are all the same .wav file analyzed to death with all the common progs used. Let me know if there's any others that work well.

In this case, CEP seems to be best for Spectral Analysis, and Audacity is best for Frequency Analysis (thanks to ffooky for the good advice).