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Author Topic: Does digital drift exist? (marco benevento at schubas chicago cont)  (Read 1829 times)

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Offline Elguapo511

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i recorded this show w four miss on the stage (dr2d four track recorder)
Then I plugged in a two track recorder (dr07) to the sound board.

no problems. and a totally radical show.
but

I loaded them all into audacity and aligned them, yet there is still drift at the end.  Does digital drift exist.

What tools do are available for making a matrix and do i have cut the tracks and re align every track?

thanks for any help.

Online kingdong

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #1 on: April 15, 2018, 06:15:06 PM »
Two different devices may/will have internal clocks that run at slightly different speed.  Over the length of a whole show you will usually see a slightly different file length.  When I have to fix this I typically use Audacity and stretch the shorter file to be the length of the longer.
http://manual.audacityteam.org/man/change_speed.html

The process I loosely use is to open both waveforms in the same Audacity project and align the beginning of the files.  Then I go the the end of the files and look for an identifiable peak.  I will note the time difference between the two and use that amount to stretch the shorter file.  Since we are typically talking about less than a second over the course of a set I don't worry about the very slight pitch shift that this will induce.  I haven't noticed it to cause phasing issues or other atrifacts, but I don't have the most discerning ear on this forum by a long shot.

Offline if_then_else

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #2 on: April 16, 2018, 01:28:49 AM »
Even if the tracks are aligned perfectly there might be some issues with the timestretching / pitch correction algorithm on the resulting mix-down file  - e.g. depending on the genre. E.g. I was having some issues with 2 psychedelic rock and drone music recordings and the default algorithm in Samplitude 10.2. No issues with the same project and the "élastique pro" algorithm.
« Last Edit: April 16, 2018, 03:03:19 AM by if_then_else »

Offline Elguapo511

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #3 on: April 16, 2018, 04:31:48 PM »
gotcha.  this is what i was looking for.  Ill give it a try.

also,  any real time eq available for mac? and free

Offline Elguapo511

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #4 on: April 17, 2018, 12:20:29 AM »
sooo.... i recorded the show with four mics and two soundboard channels.

is there a way to mark a point in one track, then mark another point in another track.  then match those points up automatically.


I am having trouble aligning the tracks, i can't seem to get them together.   

i used math, and the track move tool.

just wondering if I can do it with less guessing.

thanks

Offline if_then_else

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #5 on: April 17, 2018, 01:57:13 AM »
Set a marker at a single cymbal or kick drum hit at the beginning of the show.
Do the same thing for a single event at the end of your first stereo track.
Now lock the individual channels and vary the time stretch factor on the second source until both stereo tracks are aligned correctly.
Listen back to the aligned tracks. If they still sound out of phase, unlock the second source and carefully move ("nudge") the stereo track to the left or right by a few samples. Repeat until you're happy with the result.
With my own recorders and the typical distances at small to medium sized venues you're looking into a ratio of ~1.000004:1 - ~1.000006:1.

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Offline nulldogmas

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #7 on: April 17, 2018, 04:16:35 PM »
Set a marker at a single cymbal or kick drum hit at the beginning of the show.
Do the same thing for a single event at the end of your first stereo track.
Now lock the individual channels and vary the time stretch factor on the second source until both stereo tracks are aligned correctly.
Listen back to the aligned tracks. If they still sound out of phase, unlock the second source and carefully move ("nudge") the stereo track to the left or right by a few samples. Repeat until you're happy with the result.
With my own recorders and the typical distances at small to medium sized venues you're looking into a ratio of ~1.000004:1 - ~1.000006:1.

^This.

Note that it doesn't have to be the very beginning and very end of the show — so long as you have two good markers a reasonable distance apart, you should have enough spread to get a good measurement of the drift.

Offline wforwumbo

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #8 on: April 18, 2018, 12:13:47 PM »
Question... we’re both recorders at the same sample rate? If you had to resample one track, there will be an inherent linear group delay. With linear filters, this will result in minimal (if any audible) distortion, but it will mean that tracks won’t align without time stretching with a phase vocoder.
2x Schoeps mk21 (matched pair) -> nbob KCY -> Naiant PFA -> Sound Devices Mixpre 6

Offline Elguapo511

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #9 on: April 18, 2018, 09:15:33 PM »
both 16 bit.   but thanks for the tip.

the pics are very different and picking up different frequency is making it hard to find alignment....

Offline nulldogmas

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #10 on: April 18, 2018, 09:37:54 PM »
A loud clap, start of PA music, anything? It doesn't have to be perfect alignment, just closer than what you have now.

Offline Elguapo511

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #11 on: April 18, 2018, 09:59:11 PM »
this is pretty impossible.

 :banging head:

it still seems to get nuts at the end.

does it matter if i slow one down  or speed one up?

Offline noahbickart

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #12 on: April 18, 2018, 11:27:05 PM »
Question... we’re both recorders at the same sample rate? If you had to resample one track, there will be an inherent linear group delay. With linear filters, this will result in minimal (if any audible) distortion, but it will mean that tracks won’t align without time stretching with a phase vocoder.
Recording:
Capsules: Schoeps mk41v (x2), mk4v (x2), mk22 (x2), mk3 (x2), mk21 & mk8
Cables: 2x nbob KCY, 1 pair nbob actives, Darktrain 2 and 4 channel KCY extensions:
Preamps:    Naiant Littlebox, Naiant IPA, Naiant PFA, Sound Devices Mixpre6
Recorders: Sound Devices Mixpre6, Sony PCM m10

Home Playback: Mytek DSD 192> McIntosh MC162> Eminent Tech LFT-16; Musical Fidelity xCan v2> Hifiman HE-4XX / Beyerdynamic DT880

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Offline nulldogmas

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #13 on: April 19, 2018, 07:30:39 AM »

does it matter if i slow one down  or speed one up?

Nope.

Offline capnhook

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Re: Does digital drift exist? (marco benevento at schubas chicago cont)
« Reply #14 on: April 19, 2018, 08:22:25 AM »
this is pretty impossible.

 :banging head:

it still seems to get nuts at the end.

does it matter if i slow one down  or speed one up?

Are you using a version of Audacity, other than V2.1.0?
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