Topic: Mic / SB Matrix Time/Phase Shift

[nulldogmas]

Yeah, be careful with that "slight delay between channels" stuff.  I pulled a board feed at a local venue (later mixed with mics) and the traveling FOH was a little too heavy in that channel-delay trick.  In post, when I laid out the tracks in Soundforge, I didn't initially notice the delay and after mixing with the mics and using the 1 foot per ms formula, the result was echo-garbage. 

That's bizarre. Why would the FOH need to impose artificial fake room echo when they have an actual, you know, room to work with?

I'm equally baffled by the occasional soundfolk who lather on the plain old reverb on vocals to absurd levels, especially in fairly wet rooms. But topic drift, I know.

[robgronotte]

Could someone tell me how I can easily delay one channel when doing a SBD/AUD mix in Audacity?

I have found a few tutorial videos which show you how to use the Latency function, but that seems to be for when you are recording a new track with a microphone, not working with two existing tracks.

I guess I could just delete the correct amount of time from the beginning of the AUD track, but it seems like there must be a better way.

[AbbyTaper]

Can't you just add silence to the start?

[robgronotte]

Can't you just add silence to the start?

Yes, I guess I could do that also, but either way now the two recordings won't be the same length which gives me another issue to deal with.

[Gutbucket]

There are various ways of doing it via shifting, adding, cutting, delaying.  Haven't used Audacity in a long while, but can't you shift alignment by clicking and dragging one stereo pair along the timeline while leaving the other in place?  May need to unlock the track first to allow movement, and zoom in enough so that the shift is relatively small (on the order of milliseconds), but you'll need to zoom in to near that level to accurately see the position of the transients anyway.  In that way its easy to play around with alignment while listening to get it just right.

[unidentified]

I am no expert, but I have dabbled successfully more than a few times with synchronizing and mixing sbd and audience sources, and have two suggestions. First, the above comment about using the sound of folks talking as an indicator of accuracy is consistent with my experience,  Any trace of the dreaded "ball-park echo effect" in on-stage banter between tracks in a mix I produce tells me that I have to try again. Second, in open situations in fairly modestly-sized rooms, my best friend is a D Day-style "cricket" -- a brass clicker as used in WWII that you can buy on Amazon for about $10 and which produces a distinct and precise click-clack sound that is very easy to find on the wave forms of the two sources.  Ideally, you click it after you start rolling and before the set starts and then again after the set ends and before you stop rolling.  Works for me but YMMV.

[Gutbucket]

^ I keep a similar dog training "cricket style" clicker in my recording bag.  Little rectangular plastic thing with a spring steel thumb plate in it.   I bought a few of them years ago out of a big bin at a pet supply place for like a dollar or two each.  Great for making audible alignment clicks as you describe at the start and stop.  ..which is brief and generally won't call attention to what you are doing.

The clicker is also useful for hearing how the stereo distribution of your mic-setup translates on playback, if/when you ever get a chance to walk all the way around the recording position at some distance while clicking / calling out each of the 12 clock positions before or after the performance.  Super interesting thing to do.  But unlike a couple alignment clicks, this will call attention to what you are doing and generate looks!  Pick your opportunity wisely.

[unidentified]

^ I keep a similar dog training "cricket style" clicker in my recording bag.  Little rectangular plastic thing with a spring steel thumb plate in it.   I bought a few of them years ago out of a big bin at a pet supply place for like a dollar or two each.  Great for making audible alignment clicks as you describe at the start and stop.  ..which is brief and generally won't call attention to what you are doing.

The clicker is also useful for hearing how the stereo distribution of your mic-setup translates on playback, if/when you ever get a chance to walk all the way around the recording position at some distance while clicking / calling out each of the 12 clock positions before or after the performance.  Super interesting thing to do.  But unlike a couple alignment clicks, this will call attention to what you are doing and generate looks!  Pick your opportunity wisely.

Clearly, great minds think alike, Gutbucket!   

[Gutbucket]

  

[nulldogmas]

Can't you just add silence to the start?

Yes, I guess I could do that also, but either way now the two recordings won't be the same length which gives me another issue to deal with.

As others above have noted, you're not trying to get the two recordings to be the same length; you're trying to get them to align throughout the course of the music, which is slightly different.

My workflow, which I've been following for a mind-numbing number of Merge festival tracks now, is:

1) Import both tracks into Audacity.

2) Trim the start of one track or add silence to the other until the first big spike of amplitude aligns. (I do this visually while zoomed in by an extreme amount, then check to hear that it sounds okay, which it always does.)

3) Scroll to near the end of the recordings, and find a clear loud fast-attack spike (snare drum hit is usually good) in both recordings.

4) Click on the spike in one recording, change the Selection display to "Samples," then copy down the number.

5) Click on the same place in the spike in the other recording, and drag to select everything between there and the start of the recording.

6) Effect > Pitch and Tempo > Change Speed and Pitch, then type the number from step 4 into "New Length."

Done. There will be a teeny amount of drift in any part of the recording after that late spike, but it won't be enough to be noticeable over the few minutes left to run at that point.

[morst]

Could someone tell me how I can easily delay one channel when doing a SBD/AUD mix in Audacity?

I have found a few tutorial videos which show you how to use the Latency function, but that seems to be for when you are recording a new track with a microphone, not working with two existing tracks.

I guess I could just delete the correct amount of time from the beginning of the AUD track, but it seems like there must be a better way.

F5 (function 5) gives you the double headed arrow tool which enables sliding tracks left-right.
If you really mean ONE CHANNEL then you will need to split stereo track first, which is hidden in the downward pointing triangle to the right of the track name

[AbbyTaper]

There will be a teeny amount of drift in any part of the recording after that late spike, but it won't be enough to be noticeable over the few minutes left to run at that point.

Thanks for adding that Neil.  I've seen a number of times where people say there won't be drift "because both sources are digital".  In my experience there is ALWAYS some small amount of drift.

[nulldogmas]

There will be a teeny amount of drift in any part of the recording after that late spike, but it won't be enough to be noticeable over the few minutes left to run at that point.

Thanks for adding that Neil.  I've seen a number of times where people say there won't be drift "because both sources are digital".  In my experience there is ALWAYS some small amount of drift.

There shouldn't be drift in the section where you change the pitch and tempo of one source to match the other, because you just changed them to match. After that they'll still run at slightly different speeds, but it shouldn't be noticeable over a span of just a few minutes.

[robgronotte]

I did mean shifting one source, not one channel.

In this particular case there shouldn't be any drift because both sources were recorded at the same time on the same multi channel recorder, so the recordings are exactly the same length and only issue to deal with is the very slight time delay of the microphone source. I visually found it to be about 20ms, small enough that I can't hear any echo effect, but it was recommended to me that I try to account for that.

After this I do plan to tackle a matrix of two sources recorded on different devices though. It still seems odd to me that there would be a drift in digital recordings, but I will try to check for it.

[AbbyTaper]

I did mean shifting one source, not one channel.

In this particular case there shouldn't be any drift because both sources were recorded at the same time on the same multi channel recorder, so the recordings are exactly the same length and only issue to deal with is the very slight time delay of the microphone source. I visually found it to be about 20ms, small enough that I can't hear any echo effect, but it was recommended to me that I try to account for that.

After this I do plan to tackle a matrix of two sources recorded on different devices though. It still seems odd to me that there would be a drift in digital recordings, but I will try to check for it.

If both your sources went into the same recorder there won't be any drift.