Kemper "Popping" issue when playing through DAW and audio track

newb3fan

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1,355
I've had my KPA for 2-3 months now. I continue to get a sporadic short "popping" noise while I'm playing in my studio. The setup is: guitar-keeper-mains out in stereo to inputs 1 and 2 on apogee duet-audio track in Logic Pro. Computer is an iMac about 2014 age with 32MB RAM. I have been working with a customer service rep at Kemper. I cannot figure out why it is doing this. It is not specific to any rigs, clean or crunchy. It happens very sprodically. It is not a loud or long pop but it is there and I'm getting annoyed. It does not happen when I listen through headphones. I switch out the computer to an older iMac we have in the house with the same interface and running into garage band. It did not make the pop noise when I tested for 5-10 minutes. All the electronics in the setup are running through a Furman before going into AC power. I even tried switching to an isolated circuit in the house that I know nothing else is on...it did not eliminate the problem.

Has anyone else experienced anything similar and do you have any other suggestions for what I can try to resolve this? It's putting a damper on an otherwise great guitar/recording experience with a great piece of gear.
thanks,
Mike
 

newb3fan

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1,355
yes the pop is heard and recorded. IDK what a word clock is or which device is the master. Looks like I have some reading to do! Thanks for the post for me to check this out.
 

jwnc

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154
Are you using the main analog outs or the SPIDIF?
Do you hear it during the track playback after its been recorded?
Does it happen on all profiles?
 

burningyen

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15,099
The only time I experienced popping/crackle with my KPA was when I tried to record via SPDIF. It's odd that you're hearing it with the main outs.
 

newb3fan

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1,355
This is copy/pasted from the sweet water.com site...for those that ever encounter this type of issue in the studio.

This is a question I get a lot. Word clock is one of the most commonly misunderstood and enigmatic topics in the studio. Here's my explanation...
Every digital device, from a simple portable CD player to a Pro Tools HD rig, has a word clock. Not to be confused with sync clock (like MTC or SMPTE), word clock is what tells a A/D or D/A converter when to take the sample. It fires an impulse to the converter 44.1k (or 48k, or 96k, etc) times per second. The reliability of this clock, how evenly spaced those pulses are, determines the accuracy of the conversion process.
If you have digital connections in your studio (S/PDif, lightpipe, etc), you MUST have a single clock source. If multiple devices are each trying to be the master clock, you will probably experience pops, clicks, or sometimes chirps in your audio. The solution is usually to make sure that you only have one master clock, and that all slave units are getting a clean clocking signal.
But even without obvious problems like pops and clicks, you may still have more subtle word clock problems. Think of it like this...
Ever seen clips from the very early days of film? Back in the days of hand-cranked cameras, it was extremely difficult to get the shutter speed to be perfectly even. The result was a moving image that, when played back at a constant shutter speed, seemed "jittery." the motion was often jerky an unnatural. This was due to the imperfections of the original film speed.
The same thing happens in digital audio. The more "jitter" present in the clock source, the less accurate the resulting conversion will be. Jitter is manifested in audio as phase distortions and discepancies, particularly in the higher frequencies. They can lose some of their sparkle, transients can lose some attack, and stereo images aren't as vivid.
Improving the quality of your clock is an easy way to upgrade every A/D and D/A converter in your studio. In most cases, adding a high-quality master clock, such as Apogee's Big Ben or Antelope Audio's Isochrone OCX will result in a marked improvement in the overall quality and clarity of your finished product.
But what if you don't have a master clock? One of the hallmarks of Apogee and other high-quality converters is usually a low-jitter clock. If you have a great converter in your system, you can feed that clock source to everything else with an A/D or D/A converter on it (like an audio interface, for example). Replacing the built-in clock of your interface with the clock signal from the master clock will dramatically improve the quality of the conversion being performed by the interface. There are still other factors at play, so it's not identical to running the same signal through the high-quality converter, but it is usually a very noticeable improvement.
For more on this topic, check out my friend Nika Aldrich's book Digital Audio Explained for the Audio Engineer, available through Sweetwater.
 

newb3fan

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1,355
Are you using the main analog outs or the SPIDIF?
Do you hear it during the track playback after its been recorded?
Does it happen on all profiles?

Main Outs in Stereo JW...
And yes it is not specific to any one or particular type of rig.
 

jwnc

Member
Messages
154
Does it only happen with the Kemper plugged into the Apogee?
If you record a direct DI track with the same hardware, etc does the pop happen?
I really don't think its the Kemper since its just sending an analog signal out.

The word clock won't matter here because you are using the analog out of the Kemper.
The Apogee is the main clock so that should not really be the case here generally.

What is the audio buffer for the Apogee set at? Are you using direct monitoring if it supports it?
 

newb3fan

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1,355
Does it only happen with the Kemper plugged into the Apogee?
Yes. I have never had this recording instruments or vox with the apogee previously.
If you record a direct DI track with the same hardware, etc does the pop happen?
I'm not sure I follow you here? Do you mean just do instrument directly into apogee into a track in Logic?
I really don't think its the Kemper since its just sending an analog signal out.

The word clock won't matter here because you are using the analog out of the Kemper.
The Apogee is the main clock so that should not really be the case here generally.

What is the audio buffer for the Apogee set at? Are you using direct monitoring if it supports it?
The clocking sample rate is set at 44.1kHz. Is this what you mean?
 

newb3fan

Member
Messages
1,355
Logic can react this way with too small buffer size settings. I'd look into that.
How dumb of me not to think of this...took the i/o buffer size from 32 to 64. Resulting total latency is 5.8ms...and no occasional pop from what I've listened to in the last 10 minutes of playing. Thanks space jazzer!
 




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