In my previous post, I discovered the that the bass track used by Glee had been subtly altered from Coulton's track. At the end, I tentatively made the naive assumption that there would be no reason for them to re-record the bass track if they were working off of Coulton's original. But science doesn't assume anything. In fact, Paul Potts reminded me of a very good reason to re-record the bass. Namely center-canceling. He explains it well on his blog, and goes on from there to compellingly demonstrate which specific version and file format of Coulton's audio track would have likely been used -- a feat which I find nothing short of remarkable.
Essentially, center-canceling (aka center-kill or vocal-kill) is a technique where the left channel and right channel are split and one is inverted before adding them back together. This effectively mutes any sounds which are dead-center in the track. It's often used to eliminate lead vocals to create karaoke tracks, but since the bass is usually centered, it also removes the bass. Paul was looking at using the technique to try removing (most of) the duck quack from Coulton's source, but then he struck upon the genius idea of also center-cancelling Glee's track.
I was able to reproduce this result, and it results in a much cleaner track, with no bass or lead vocal. That lets me do what I had originally had intended to do -- compare the rhythms of the banjo and mandolin tracks. Unfortunately, these parts still get easily buried in a wash of strings, backing vocals, and compression, even after I apply heavy EQ. They're still kind of quiet, but I think there's enough there to go off of. In addition to using a center-cancelled and EQ'd version of the backing track, I also slowed the tempo waaaay down, which makes the precision of the timing easier to hear. It also lowers the pitch. A lot. What were originally high-pitched compression artifacts in the mp3 become annoyingly noisy background chatter.
I'll let the results speak for themselves.
Example 1 -- Intro Riff and Beginning of First Verse
This is the longest example, because I wanted to demonstrate how well the parts stay together over a long period of time. What you will hear on this tracks is: (1) only JoCo's solo banjo and mandolin parts mixed together on only the left speaker; followed by (2) only the Glee version, modified as described above, on just the right speaker; finally followed by (3) the two of them together (JoCo on the left, and Glee on the right).
First, we'll hear it at full speed:
Then, we'll slow the whole thing down to a staggering 30% of full speed. This track is over 3 minutes long, but it really demonstrates the precision over a long period of time:
To my mind, it is absolutely inconceivable to consider the possibility that someone could deliberately perform something so precisely at full speed.
Example 2 -- Added Fret Noise
As I was looking for distinctive spots on the banjo track to test, I came across this one distinctive little riff between phrases (after the lyrics "average groupie"). The banjo and mandolin have a sort of quick syncopation going on here, but what made it extra distinct was that it had extra fret noise in the track, which I discovered wasn't in Coulton's track. The riff itself is dead on, but it appears that the audio engineers actually added a fret noise to the track as they were editing. I can only speculate why they might do that (this particular section of the verse seems to have been cut from the final screen version, so it probably wasn't a foley effect). As before, this will start with JoCo on the left, then Glee on the right, then both. Note that while I'm only playing the banjo and mandolin (as before) I did verify that this noise isn't in the other tracks.
We'll listen at 50%:
Example 3 -- The Quack
As long as we're cleaning things up and slowing things down, we may as well listen to the "ghost of a quack" that Paul discovered in the track. Bear in mind that we are not listening for an actual quack, but for the
artifact that was left over when the quack was almost center-cancelled. This sound comes just at the end of the following clip. As before, I start with Coulton's banjo & mandolin on the left (for reference, but no quack), then just Glee on the right (there's a sort of "click" near the end), and then the combined version.
But in case you don't hear it, after I play the combined version, I begin to loop over the quack. And while it loops, I do something almost magical... I discovered that the quack corresponds to a sharp spike around 4 kHz, so I slowly fade away all the other frequencies except for a narrow band at 4 kHz. This effectively isolates the sound.
Here's what it sound like at 40% speed:
And here's what it sounds like when you bring it back up to tempo (just the mixed version this time). This actually sounds pretty annoying:
At this point, if I were on a jury, I don't see how there could be any reasonable doubt that these are the same tracks. To get something to match so closely at such a speed would be a super-human feat. And we already saw from the bass analysis that they just weren't that concerned with getting an exact match (nor would any sane person). So while the bass track appears to have been removed with the duck (and maybe lead vocals), the banjo and mandolin tracks do indeed seem to be none other than Coulton's. Which is what everyone suspected all along.