Topic: Audacity Matrix Question (loss of bass)

[johnw]

Not sure where else to put this. I recorded Umphrey's McGee 2 nights ago with Schoeps mk4V>V2 and mk41>744 both recorded into the 744 at 24/48. I loaded the 4 mono files into Audacity, adjusted the gain and then exported it to a stereo file. I also made stereo files for the individual 4V and 41 tracks. Individually these have significantly more bass than the matrix file when I'm listening to them. I think this can be caused by phase cancellation, but I'm not sure how that could have occurred. I can upload 3 of the same tracks somewhere if that would help. Any ideas?

[vanark]

If you invert the phase in one of the sources, it will be fixed. 

[johnw]

Is it possible from looking at a .wav file to tell if it's out of phase? Why would one of the sources be out of phase? I know that was a problem with V3s but I've never heard of that happening to a V2 or a 744. I wouldn't think a cable would be the cuprit.

Full lineage is:

mk41>Nbox Cable>Naiant PFA>darktrain XLR>744 (1,2)
mk4v>KCY>Naiant PFA>darktrain XLR>V2>darktrain RCA to mini XLR>744 (3,4)

Is there any other reason the bass would be lost on the matrix?

[vanark]

If you invert the phase in one of the sources, it will be fixed.

It is easy to invert the phase and check out the results.  No hand wringing necessary.

[page]

Yeah, that's my first thought as the bass cycles are slow enough that you'd end up with cancelation compared to just comb filtering in the upper frequencies. You can visually check polarity by seeing if a drum snap is starting going up or down.

My second guess would be poor alignment and things need to be adjusted in time one way or another by a handful of milliseconds (assuming the two pairs were close together in space). Still phase cancelation, but a different cause.

[Gutbucket]

If the sources are synced and aligned, you can zoom in to look at the large, low-bass waveforms which should be all going up or down pretty much across all channels more or less evenly. If one channel or a pair is obviously going down on the largest half-waves when the others are going up, invert polarity on that channel or pair.  But regardless of the visual appearance, rely mostly on flipping polarity back and forth while listening for the difference in the bottom  end.

Could be caused by different mic locations.  Might be on set of the PFAs (my PFAs invert my DPAs). Could be an XLR cable with pin 2 & 3 crossed.

[johnw]

Mics were on same shockmount so not a spacing issue. I just dragged the files into the audacity so I don't think it's a timing issue. When I muted either channel during playback both sounded fine (bass wise). I ended up inverting the mk4v file and the bass was fine on the matrix, so I think it's phasing. It sounds ok, kind of too much bass and mid range but listenable. I'll post the link to the archive file

[page]

Mics were on same shockmount so not a spacing issue.

hmm... Less likely, sure, but not necessarily.

Have a 30 second sample of all four individual tracks? Worst we could do is go "well, yeah, dunno."

[johnw]

I'll make up some samples in a bit. Thanks

EDIT: actually I realized I deleted the original wav files. I can post stereo tracks of the 2 sources if that would help.

[johnw]

mk41: http://www.mediafire.com/listen/bmtdmfiafm8q6tx/41.wav
mk4v: http://www.mediafire.com/listen/iu1w69actacqhb8/4v.wav

30 seconds from the start of Ringo

[hoserama]

Loaded the files into Audition and looked at the wave form. Folks here are very correct--the files are phase inverted to each other. Night and day difference when you flip the polarity.

[hi and lo]

I'd need to fire up Spice to re-confirm, but the signal for the Nbox vs. KCY are from different legs of the FET (laymans terms... different polarity). Pretty sure all nbox recordings are phase inverted and ran into this plenty of times trying to matrix them with other AUD sources.

[page]

I'd need to fire up Spice to re-confirm, but the signal for the Nbox vs. KCY are from different legs of the FET (laymans terms... different polarity). Pretty sure all nbox recordings are phase inverted and ran into this plenty of times trying to matrix them with other AUD sources.

and that is an interesting fact I didn't know (but makes sense).

[johnw]

Awesome information! The mk4Vs were on Nbox cables and the 41s were on a KCY. Makes total sense. I inverted the 4Vs when I made the Matrix and the bass was present again so that's what I shared on archive.org. I'll just need to remember to invert any Nbox recordings for future Matrix recordings.