Stereo/Mono Question

egproductions

egproductions

Veteran
So when I record audio onto my Canon XL2 using my Rode video Mic, I record the same audio too two channels at the same levels. When I am editing the audio in audacity or audition, I like to convert it to mono so that I can have a lower bitrate and still have the quality be good. But when I convert it, it doesn't sound as full. Why is this? Shoudln't it sound the same considering its a mono mic and is the same audio on the left and right channel? Below are links to the two samples.

http://egproductions.tv/transfer/1.mp3 - Stereo
http://egproductions.tv/transfer/2.mp3 - Mono
 
egproductions said:
So when I record audio onto my Canon XL2 using my Rode video Mic, I record the same audio too two channels at the same levels. When I am editing the audio in audacity or audition, I like to convert it to mono so that I can have a lower bitrate and still have the quality be good. But when I convert it, it doesn't sound as full. Why is this? Shoudln't it sound the same considering its a mono mic and is the same audio on the left and right channel? Below are links to the two samples.

http://egproductions.tv/transfer/1.mp3 - Stereo
http://egproductions.tv/transfer/2.mp3 - Mono
Click to expand...

Well, the first link that you gave, labeled as stereo, sound like it has some massive phase cancellation. The second one sounds great. The file you have labeled as "mono" actually sounds better than the one labeled "stereo." Are you sure that you didn't switch the two files?

How is your Rode connected to your camera? Something is amiss here.

And for clarification, you aren't recording in stereo. It's dual mono. That gets confusing because most audio editing apps refer to all two-channel files as stereo.

Your best bet is to remove one of the two tracks of audio, rather than combine them into a "mono" document.
 
egproductions said:
So when I record audio onto my Canon XL2 using my Rode video Mic, I record the same audio too two channels at the same levels. When I am editing the audio in audacity or audition, I like to convert it to mono so that I can have a lower bitrate and still have the quality be good. But when I convert it, it doesn't sound as full. Why is this? Shoudln't it sound the same considering its a mono mic and is the same audio on the left and right channel? Below are links to the two samples.

http://egproductions.tv/transfer/1.mp3 - Stereo
http://egproductions.tv/transfer/2.mp3 - Mono
Click to expand...

Hi! I analized your audiofiles and the stereo file has one channel with the phase inverted. I imported them into Nuendo and exported again like two mono audiofiles, then reimport those and voilá, almost 100% freq cancellation. Just invert the phase of one channel and you should be ok.

The problem may reside on the software or maybe the cable that you used for the videomic.

Hope it helps.
Best Regards.
Fernando
 
I'm a little lost. Can you give a quick explanation on phase...isn't phase a delay..how can it be inverted? I connected the mic to the front mic jack of the XL2, If I heard the sound OK, I didn't realize there could be a problem.

If the Mono one is sounded correct to you its because I split the dual mono track, got rid of one of th tracks turned the other into mono (I didn't combine both stereo tracks into one mono)

Thanks for the help
 
egproductions said:
I'm a little lost. Can you give a quick explanation on phase...isn't phase a delay..how can it be inverted? I connected the mic to the front mic jack of the XL2, If I heard the sound OK, I didn't realize there could be a problem.
Click to expand...

From "the Audio Dictionary" 2nd ed. by Glenn D. White (a great book to have around)
Out of Phase A condition where two signals have a phase difference of 180 degrees, or one-half cycle. It should be called "out of polarity," phase being a continuous variable rather than discrete.​
Consider a typical sine wave: it oscillates between the positive and negative sides of a rest point. Inverting the phase of that sine wave will essentially flip it upside down, so that the positive peaks become negative peaks and vice versa. Add the inverted waveform to the original waveform, and they cancel out. Similarly, introducing a half-cycle delay will have a comparable effect.

An improperly wired cable can easily introduce this phase inversion if the positive and negative pins on one end of the cable are connected to the negative and positive pins (respectively) on the other end. By itself, the inverted signal isn't a big deal, but once you add it to another signal (with the original phase) then you'll start having frequencies cancel out.

In stereo, phase becomes important for another reason. When audio is played back on both speakers in-phase and at equal level, the listener will perceive the sound as coming from a "phantom center" located between the two speakers. Lower the level of one of the speakers, and the sound will appear to move towards the other speaker. However, if the two tracks are out-of-phase, the imaging illusion becomes messed up and will sound unfocussed and unnatural.

But wait, it gets worse: some mono playback systems (TVs, radios, even some broadcasters) will take the left and right signals, add them together, and play the resulting summed signal. This can be disastrous if there was any important information that was out of phase. I've seen corporate videos where the narration mysteriously vanished during an important client presentations, leaving only the sound effects and music (and a thoroughly embarrassed producer). That is why it is absolutely critical that you always check back a mix by summing it to mono and playing it through. Out of phase audio can also wreak havoc on some phase-based surround decoding systems, causing out of phase narration to wander onto the rear speakers.

Both C2V and Fernando are right about how to solve this problem, although I would tend to go with C2V's simpler solution. Additionally, go through your post-production setup and double-check the phase on all your cables. Whip up some mono "pink noise" and play that back through both speakers; if it shows up as a nice and tight center image, then your in business. Otherwise, you could have an out of phase speaker.
 
Excellent explanation SMuir! One last advice, every time that you have mono source (VO) don't use multiple Mono channels, just use 1 Mono channel ( can be a Mono VO bus ) to avoid phase cancellations.

Best regards
Fernando
 
nyquist-x said:
Excellent explanation SMuir! One last advice, every time that you have mono source (VO) don't use multiple Mono channels, just use 1 Mono channel ( can be a Mono VO bus ) to avoid phase cancellations.

Best regards
Fernando
Click to expand...

I would take that a step further. It's not a bad idea to record two channels, but set the audio level of one of them lower than the other. This can cover your rear if you accidentally get some overmodulation or clipping from a sudden loud bit of dialogue or sound -- just use the dialogue or sound from the other channel, recorded at the lower level, for that piece.

But yes, only use one of the channels in editing, not both. Completely avoids the whole phase issue.
 
Adding to David's advice: when cutting dialogue that was shot using the tried-and-true technique he describes, you may wish to lay down a track of the louder (often also the least noisey) version of the take, splicing in (with cross-fades) the quieter track to cover momentary overloads (coughs, shouts, etc.). If that's the case, then you'll definitely want to double-check the phase of the two tracks; if they're out of phase (add them together and they get quieter), then you should print a phase inversion effect into the safety track.
 
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