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Author Topic: Small blip of increase in waveform amplitude, what's the cause and how to fix?  (Read 1382 times)

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Offline ycoop

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This is totally inaudible before I apply amplification, after which there's a tiny snippet of clipping. Haven't managed to take care of it with a limiter without hearing a change. Any input?

Mics: Avantone CK-1s, CA-14 omnis
Pres: CA9100
Recorders: DR-60d mkII, DR-22wl, DR-07

Offline ycoop

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Didn’t identify what caused this, but ultimately I split the stereo track, selected the section with the blip, and compressed it until it was in line with the rest of the waveform, merged split tracks back to a single track and then amplified to -1.0 dB. Still has a nearly inaudible little blip, but it satisfactorily fixed the issue.
Mics: Avantone CK-1s, CA-14 omnis
Pres: CA9100
Recorders: DR-60d mkII, DR-22wl, DR-07

Offline bombdiggity

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That is likely a minor mic bump or slight cable pinch. 

Actually the best fix for something like that is in Audition (in Audition 3 : Effects > Restoration > Click/Pop Eliminator) just highlighting that tiny section of the left channel (a smaller area than the view you show).  That should make it disappear. 
Gear:
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Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
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Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline rigpimp

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Warts and all...

If it is there and it really bugs you then fix it.  If you amplify and it is still barely audible then leave it in.

Just wait until you make a whole recording that is simply unlistenable.  Not trying to jinx you but we all do it at some point.  Its part of "the curve"

Shrug it off but test your cables and connections in the controlled environment of your home.

Easy fix: Zoom in an copy other channel
Moderate fix: Use on-board click control on your DAW software of choice
Expensive fix: Use expensive audio restoration software to perform click or spectral repair.

Good luck!
Mics: Schoeps MK5 G MP, Schoeps CCM 4 Lg MP, Schoeps MK8 MP, nBob cables > PFA, KCY 250/5 > PFA
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Recorders: Sound Devices Mixpre-6, Sony PCM-M10
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Offline ycoop

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Just wait until you make a whole recording that is simply unlistenable.  Not trying to jinx you but we all do it at some point.  Its part of "the curve"

My first time out trying to record with a handheld recorder I ended up next to small table top fan that was being used to cool some equipment. During the acoustic portion of the show it made things nearly unlistenable. I ended up having to do major work in post that left severe artifacts. I give the surroundings a good hard look now to identify any sources of fan noise (and I ended up buying those Movo windscreens :))
Mics: Avantone CK-1s, CA-14 omnis
Pres: CA9100
Recorders: DR-60d mkII, DR-22wl, DR-07

Offline nulldogmas

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If it's that short a blip, you could also probably get away with patching it from the other channel and it wouldn't be noticeable.

Offline ilduclo

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find zero crossings for both channels, cut

Offline ycoop

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find zero crossings for both channels, cut

This sounds like useful advice, but with my current knowledge and skill set I can’t figure out what you mean (even with help from Google).
Mics: Avantone CK-1s, CA-14 omnis
Pres: CA9100
Recorders: DR-60d mkII, DR-22wl, DR-07

Offline ilduclo

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might just be my program does that? I use an old Cool Edit Pro. Send me a flac and I'd be glad to do it for you. You can then decide if you like how it sounds.

Offline morst

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find zero crossings for both channels, cut

This sounds like useful advice, but with my current knowledge and skill set I can’t figure out what you mean (even with help from Google).
The suggestion is to copy the good channel over the bad one, but to do so at a point where it will not be noticeable.

A zero crossing is exactly where the signal goes from the positive to the negative or vice versa. In order to make the most seamless transition, I've found that you need to find a spot to start the patch where both the left and right channels cross zero in the same direction at the same point in time (up from neg to pos, or down, it doesn't matter as long as they're the same for each signal) and end it the same way (again, the in and out points need to have consistent "momentum" but it doesn't matter if it's going upwards or down on any given channel.) Think of a speaker cone trying to make the waveform. If the signal changes direction abruptly, the speaker will have no choice but to CLICK in protest!!

I think I need to illustrate this with pictures, but I'm getting tired at the moment. . . Here is someone else's description- https://ask.audio/articles/6-tips-for-vocal-editing

My main point is that the waves should not have a drastic change of direction at your edit point. One nice thing about my linked article is that the author reminds me that a zero crossing can be described as "momentary silence."

Happy to clarify, please feel free to ask follow up questions here or in PM.
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Offline ycoop

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Thanks morst that was quite helpful. I was satisfied enough with my solution to upload the show to the archive, but might give this solution a try for the learning experience.

ilducio, I appreciate the offer but given my satisfaction with the solution I went with sending out the flac is more hassle than it’s worth.
Mics: Avantone CK-1s, CA-14 omnis
Pres: CA9100
Recorders: DR-60d mkII, DR-22wl, DR-07

Offline Gutbucket

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Here is someone else's description- https://ask.audio/articles/6-tips-for-vocal-editing

My main point is that the waves should not have a drastic change of direction at your edit point. One nice thing about my linked article is that the author reminds me that a zero crossing can be described as "momentary silence."

I may be picking nits, but I can't let this one slip by.  On quick glance, the linked article is accurate.. except for the "momentary silence" quip!   A zero crossing does not represent momentary silence anymore than any other single point elsewhere along the waveform.   If its a "crossing" that indicates a degree of positive or negative slope which specifically translates to not being a moment of silence.  Momentary silence would be represented as a fully horizontal line segment without any positive or negative trending slope to it.

The key is keeping the same slope on both sides of the edit without a sharp discontinuity.  Cutting on zero crossings is a way to automatically do that easily.  Most editing software either does so by default, or you can specify that it do so somewhere in preferences or it may be specified by how one selects a region or cut point.
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Offline morst

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I may be picking nits, but I can't let this one slip by.  On quick glance, the linked article is accurate.. except for the "momentary silence" quip!   A zero crossing does not represent momentary silence anymore than any other single point elsewhere along the waveform.   If its a "crossing" that indicates a degree of positive or negative slope which specifically translates to not being a moment of silence.  Momentary silence would be represented as a fully horizontal line segment without any positive or negative trending slope to it.

The key is keeping the same slope on both sides of the edit without a sharp discontinuity.  Cutting on zero crossings is a way to automatically do that easily.  Most editing software either does so by default, or you can specify that it do so somewhere in preferences or it may be specified by how one selects a region or cut point.

Good points. One thing I forgot to mention is that it's sometimes tricky to get both channels to line up with proper zero crossings, but you can force it using the fade out and fade in plugins. Make a zero crossing by fading down to zero very quickly! HAHA!

I guess rather than momentary silence, you could look at a zero crossing as the point where the speaker cone is moving through its resting position, despite the fact that it is in motion!
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Offline Gutbucket

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Quote
I guess rather than momentary silence, you could look at a zero crossing as the point where the speaker cone is moving through its resting position, despite the fact that it is in motion!

Moving at rest! A dilemma of modern life.

Yes that's nominally true at the speaker. 

But it's a long path from the digital representation of the waveform in your computer to that speaker cone.  DC offset can occur at different points along the way. A misaligned power amp with some degree of DC offset will cause a voltage difference across the terminals and some amount of current to flow through the voice coil at "rest", pushing or pulling the cone away from its nominal mechanical center resting point even though no signal is present.  Ideally that's adjusted or compensated for, such that a zero crossing = zero voltage output = speaker driver at its physically balanced mechanical resting point.

Here at TS we're more familiar with DC offset on the recording side of things, where acoustic waveforms are not always symmetrical, where batteries powering microphones die slowly sometimes causing asymmetric distortion or clipping, and where amplification stages may distort or clip asymmetrically.  Ideally, zero crossing should equate to what would be the position of the microphone diaphragm at rest (even though it's never actually at rest).

Determining where the zero crossing point of a digitally sampled waveform should be is somewhat arbitrary. We can shift it to any positive or negative value we chose and define that as zero.  Should it be the average of all sample values? The averaged value of just the input noise in the absence of any other signal? The median between the highest and lowest peak values? It's easy to determine precisely where the top and bottom are, but the midway point is less well defined.  It's essentially the center point between other well-defined things.


« Last Edit: June 12, 2018, 05:26:32 PM by Gutbucket »
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Offline bombdiggity

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All these other suggestions and details are great background knowledge but not necessary for this instance. 

Cool Edit Pro or Audition (probably even Audacity) click repair will smooth that right out.  Zero in really close so you're only running it on the click.  It's also good for extremely loud close claps in very quiet passages - the jazz taping nightmare - (as long as you apply it to all of the really loud ones). 

The copying from one channel to the other (at zero crossing points) is particularly useful when you have substantial dropouts or long passages where one channel is roached and the other OK.  On a stereo recording you end up with dual mono (which can often be heard flipping back and forth from stereo to mono if the patches are extensive) but that's better than nothing or a disaster on one channel.  One of the issues that normally arises with a stereo that sometimes makes that a little less ideal is that the same sound typically appears a few samples off in one direction or the other on the two channels so finding a truly neutral point to cut and paste the same material over to the other channel can be a challenge.  The same point for the same instrument is usually in a slightly different place along the timeline in each channel (not to mention relative volume and potentially a somewhat different mix depending on how much separation you got.  If close enough a cut and paste may not be too noticeable but it may be more apparent on a transitory spike like this than a good click repair tool and it's a lot more work. 

The advice about zero crossings is particularly useful.  Always edit on zero crossings (whether adjusting levels at points, applying repair tools, whatever).   If you right click from any point in Audition that provides the option to move the cursor to the previous or next zero crossing from wherever the cursor is, which makes it very easy. 
Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline rigpimp

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ycoop, you following along at home?    :P
Mics: Schoeps MK5 G MP, Schoeps CCM 4 Lg MP, Schoeps MK8 MP, nBob cables > PFA, KCY 250/5 > PFA
Pre/A>D/P48: Sonosax SX/M2, Sonosax SX/M2-LS, E.A.A. PSP-2, Naiant Tinybox, Neumann BS48i-2 (for sale)
Recorders: Sound Devices Mixpre-6, Sony PCM-M10
Playback: McIntosh MC 2105 > McIntosh MX 130 > Von Schweikert VR-4 JR
http://archive.org/bookmarks/kskreider

Offline ycoop

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Well at work, but yeah.

Don’t have access to Audition, maybe Audacity’s click removal will work.
Mics: Avantone CK-1s, CA-14 omnis
Pres: CA9100
Recorders: DR-60d mkII, DR-22wl, DR-07

Offline bombdiggity

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I'd think any of them would on something simple like this.  It can be trial and error playing with the settings and profiles a bit to get what works best.  Audition has four models in the click and pop and a bunch of settings but I think I more or less rely on one of the defaults. 
Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline ycoop

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Audacity click removal was not successful. Tried the zero crossings cut from other channel which resulted in a small blip when the cut happens as the two tracks don’t have zero crossings at the exact same locations. I know I could do a fade in/fade out on a new track before and after the cut and then merge the tracks, but that seems like overkill when my original solution was satisfactory.

Mics: Avantone CK-1s, CA-14 omnis
Pres: CA9100
Recorders: DR-60d mkII, DR-22wl, DR-07

Offline Gutbucket

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Zoom way, way, way in on the edit point until you see the discrete sample points of the waveform.  Manually drag a few sample points to smooth out the sharp discontinuity and that will nick the blip.
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline morst

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Zoom way, way, way in on the edit point until you see the discrete sample points of the waveform.  Manually drag a few sample points to smooth out the sharp discontinuity and that will nick the blip.
Yeah, just pencil-tool right over it, if that's easier. It's just an unwanted noise, right?
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Offline Ben Turnbull

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Click repair will normally work... what bugs me more is the cause of this particular wave form/deform.  I've never pressed the issue and have always attributed it to some sort of power irregularity. Screwed up as it looks, most of the time it will "track" without a major glitch.  YMMV  :shrug:
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Offline relefunt

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I've been following this thread and reading some replies by some very smart and knowledgable people. I thought maybe we might be able to use some thoughts on the issue from someone not so smart and not so technically knowledgable (me).

If one were using Audacity I would recommend first trying the repair tool. If the noise is too many samples long in duration for that, then click repair sometimes works (there are adjustments to how sensitive and specific the tool is -- that can have an effect on what type of click is removed), or even splitting the channels, highlighting the noise, and using negative numbers with the amplify tool until it resembles the baseline, then attaching the channels back to a stereo track.

In terms of "what's the cause" -- there are countless causes of noise, as people have pointed out. Loose cables, RF interference, loose wire in the mic, a power surge from the battery/power source, and I also sometimes wonder about static electrical discharges when touching the gear to make adjustments.

Good luck. Sometimes I record a show and there are a dozen or so UNOs (Unidentified Noisy Object) and other times there are none. i wish i could see a pattern. Maybe someday. Thanks to all the people who contributed to this thread -- i continue to learn quite a bit on TS and I really do appreciate your time and effort.
« Last Edit: June 20, 2018, 03:13:09 AM by relefunt »
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