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Author Topic: Syncing R-44 SBD/AUD Matrix in Audacity (OSX) - have read sticky already  (Read 2497 times)

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Offline acidjack

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As noted, I have read the sticky on this already, but I think my question is slightly different.

I have an SBD/AUD matrix recorded on an R-44 with the mics back at the board. The board is maybe 100ft from the stage.  As I understand it, there is about a 1millisecond difference for every 50ft one is from the stage. 

I hear very little noticeable echo, but certainly looking at the waveforms, the peaks on the aud look visually a touch "later" than the SBD. 

The sticky describes lining up two recordings based on samples, which will not work for me, since both have identical numbers of samples given that I used an R-44 that recorded both exactly simultaneously.

My questions are:
1. What is the best way to "line up" the recordings - is there any feature that I'm not thinking of, or do you literally just have to zoom way in and eyeball the peaks?

2. Assuming that the answer is to chop some time off of one of them, should I chop the SBD or the AUD?  Another TSer who I trust said to chop 2msec off the SBD- but this seems counterintuitive to me as the AUD is the delayed signal.  Shouldn't I chop a tiny amount off of the AUD?

3. I have loved using Audacity and it has always met my needs, but now that I will be doing more 4ch work, is there another program that makes this much easier?  (I'd especially like to hear from people who have tried it with Audacity and another program).

The most difficult thing for me, and the other thing that the very helpful post in the sticky didn't quite address, is again, how you can measure the differences. I am frankly not that comfortable trusting my ears to determine whether it's off (especially in this case, where the delay is not very significant given room size).   I also am not entirely clear on the best way to measure the distance between two points in two separate 2ch stereo recordings.  I see how to select, say, a length of music in one 2ch recording and have it tell me the length, but I'm not sure again, because the number of samples is identical, that that is apposite to telling me how far "off" the two samples are. 

Any help much appreciated.  I know there are always a lot of questions about this kind of stuff.
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Offline Walstib62

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Re: Syncing R-44 SBD/AUD Matrix in Audacity (OSX) - have read sticky already
« Reply #1 on: January 25, 2010, 12:30:25 PM »
I don't have screenshots, but there is a time shift tool in the upper left. It looks like L/R facing arrows. Zoom in to get a good view, then select the aud track, then select the time shift tool. then just simply slide the entire waveform L/R to line the 2 up. You then do a slight cut of both at the front end, and you are good to go.

Offline Todd R

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Re: Syncing R-44 SBD/AUD Matrix in Audacity (OSX) - have read sticky already
« Reply #2 on: January 25, 2010, 01:22:02 PM »
I don't know about the specifics of audacity, but in general:

Sound travels at about 1,000 ft/sec, so it takes about 1 ms to travel 1 ft.  So if you are recording 100' from the stage/PA stacks, then your aud recording will be about 100ms delayed from the soundboard recording, not 2ms (ie, 1ms/foot, not 1ms/50').  The soundboard recording will be getting the information at the speed of electrons, on the order of the speed of light, and practically speaking, instantaneously.  The aud recording gets the information of the band playing from the PA stacks, via soundwaves, and hence it is delayed by the time the speed of sound takes to cover the distance you are from the band/stacks.

Forgetting the time shift capabilities, as you mention, the easiest way is to just chop 100ms from one recording.  And yes, you are right, you should chop 100ms from the aud recording.

Think about it this way:  if you started the R44 exactly 500ms before the band started (and pretending there is no sound at all in the room except the band), the soundboard recording would have 500ms of dead air and then the band would start playing.  The aud recording would have the 500ms of dead air from you hitting record a bit early and then another 100ms of dead air while it waited for the soundwaves from the stage/stacks to reach the mics.  If you chop off 100ms from the aud copy, then both recordings would see the music start at 500ms into the recording.

If you chop 100ms from the board recording, then the board recording sees the music start at 400ms into the recording and the aud recording sees the music start 600ms into the recording, doubling your problem.
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Offline page

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Re: Syncing R-44 SBD/AUD Matrix in Audacity (OSX) - have read sticky already
« Reply #3 on: January 25, 2010, 01:24:04 PM »
I don't have screenshots, but there is a time shift tool in the upper left. It looks like L/R facing arrows. Zoom in to get a good view, then select the aud track, then select the time shift tool. then just simply slide the entire waveform L/R to line the 2 up. You then do a slight cut of both at the front end, and you are good to go.

Yeah, the "line up on samples" bit is intended to be more of a "line up on the visual peak samples" and not a "line up on the start/stop samples".

Which ever one you chop I think is negligable, but I don't ever use the entire wav form (I'll start recording 2 or 3 minutes before the first song and leave a tail of maybe 30 seconds after the encore and any announcements I think are interesting). Render your wave form after adjusting the time difference as Walstib62 described and then chop stuff. As long as you started recording more then 5 seconds before something you are interested in keeping, you can just chop off a hand full of seconds at the beginning and end to resolve it.

I'd need more information to address your third question. I use audacity frequently, but I'm not quite sure what your trying to get at.

edit: expanded #2.
« Last Edit: January 25, 2010, 01:26:27 PM by page »
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Offline SmokinJoe

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Re: Syncing R-44 SBD/AUD Matrix in Audacity (OSX) - have read sticky already
« Reply #4 on: January 25, 2010, 04:39:29 PM »
Yes, the delay is more like 1ms per foot, and you chop it off the front of the AUD waveform to visually align.

Some people say "align the peaks".  Others say find a quiet spot and then "align the beginning of a ramp up."  I'm not sure there is a single right answer.  I generally try both and then listen to the cymbals.  If the cymbals sound like someone is rattling a coffee can with a few coins in it, keep trying.

I'm not sure if you are indoors or outdoors, but let me throw this out.  When outdoors (like a music festival) at a distance, if there is any wind at all, it seriously screws with your ability to line up your wave forms.  It has to do with that swirly phasing you hear when it's really windy, and it only effects the AUD tracks.  You'll find one spot... here I need .100 to align it.... another spot I need .080 to align it.  Everywhere you look it's something else.  Which do I choose?  I don't have a good answer for that one.  The best answer I have is "pick a spot in the middle" and don't try a 50/50 SBD/AUD mix, because that maximizes the error and it will sound like crap.  Go for something like 80/20 mix where the AUD is 6db lower than the SBD.  This way the difference becomes less noticable.  Another time I did one where the songs where 80/20 SBD/AUD, and then the applause between songs faded to 20/80 with more AUD.  That was tedious, and I doublt I'll never do that again.
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easy jim

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Re: Syncing R-44 SBD/AUD Matrix in Audacity (OSX) - have read sticky already
« Reply #5 on: January 25, 2010, 05:52:48 PM »
I don't have screenshots, but there is a time shift tool in the upper left. It looks like L/R facing arrows. Zoom in to get a good view, then select the aud track, then select the time shift tool. then just simply slide the entire waveform L/R to line the 2 up. You then do a slight cut of both at the front end, and you are good to go.

^ absolutely correct

I do not understand the why/what for of chopping off part of one source to align it with the other.  The proper alignment of two sources already clock-synced only requires finding an appropriate sync point and then sliding one source (usually the SBD) forward in time across the time ruler.  Just line them up on the time ruler, then, and then do your chop/fade at the front and end afterwards.
« Last Edit: January 25, 2010, 05:59:53 PM by easyjim »

runonce

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Re: Syncing R-44 SBD/AUD Matrix in Audacity (OSX) - have read sticky already
« Reply #6 on: January 25, 2010, 08:05:14 PM »
As noted, I have read the sticky on this already, but I think my question is slightly different.

I have an SBD/AUD matrix recorded on an R-44 with the mics back at the board. The board is maybe 100ft from the stage.  As I understand it, there is about a 1millisecond difference for every 50ft one is from the stage. 

I hear very little noticeable echo, but certainly looking at the waveforms, the peaks on the aud look visually a touch "later" than the SBD. 

The sticky describes lining up two recordings based on samples, which will not work for me, since both have identical numbers of samples given that I used an R-44 that recorded both exactly simultaneously.

My questions are:
1. What is the best way to "line up" the recordings - is there any feature that I'm not thinking of, or do you literally just have to zoom way in and eyeball the peaks?

Thats basically it...since the tracks are going to be rearranged in time, I dont think knowing the delay factor is terribly relevant. I've always assumed the goal was to have each sources events happen at the same time.

Not sure it can get any easier than Audacity and the Time Shift Tool. Especially for clock synced stuff.

Ultimately you have to look at in an editor...but you can get pretty close listening to the cymbals - ride and bell shots are good checks.

One thing I find is the waveforms dont often resemble each other as much as you might think. So - visually - a single event does help. A loud PA click between songs can be a blessing...snare hits between songs are good too.

You'll notice the output of your final mix will start to have higher peaks as your sources start to sync.

Blend to taste...

Offline Walstib62

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Re: Syncing R-44 SBD/AUD Matrix in Audacity (OSX) - have read sticky already
« Reply #7 on: January 25, 2010, 09:41:25 PM »
You can't use a constant for the speed of sound. It varies by temp and humidity, mostly temp. There's an online calculator somewhere. Google it.
Syncing sources is actually an interesting and very rewarding exercise. I've preliminarily found a good tool for syncing 2 sources from different machines.
1. Find the total time of both sources.
2. divide the longer by the shorter, resulting in a # slightly over 1.0.
Divide by 100 to get %, then plug that into the speed correction factor.
OR..
Figure that for every 1 hr. of music, more or less..
you use a speed correction factor of .0035%.
Now you can use a simple ratio based on those numbers and your actual time difference. Simple algebra.
I just started on this, and that value may change with some trial, but it's worked well twice so far....

Edit-What I meant to say was that for 1 hr. of music, .100 seconds delay equals .0035% correction factor. So by using a simple ratio,

.0035/.100=x/delay time     you can quickly calculate a correction factor for any project. It's worked for me twice now. (hope I'm doing the math correctly) If anyone comes up with a better way, (or if I made a mistake) I'd be interested to hear about it.
Thanks
« Last Edit: January 26, 2010, 10:49:29 AM by Walstib62 »

Offline rocksuitcase

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I don't have screenshots, but there is a time shift tool in the upper left. It looks like L/R facing arrows. Zoom in to get a good view, then select the aud track, then select the time shift tool. then just simply slide the entire waveform L/R to line the 2 up. You then do a slight cut of both at the front end, and you are good to go.
Thanks for this. I was unsure of how to do this after being presented with the unexpected SBD patch at a recent show. I was about 110 feet away and used 98ms using Audacity with the timeshift tool. Thanks again.!
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