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Author Topic: Sounds like clipping...but it isn't...  (Read 888 times)

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Offline ycoop

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Re: Sounds like clipping...but it isn't...
« Reply #15 on: March 21, 2018, 03:13:39 PM »
I don’t think I had auto gain control turned on, I’ll check when I’m back home.

I discovered last night that running a high pass filter set to 150 Hz with a 6 dB rolloff per octave removes the crunching sound (it also makes the recording sound like its coming from underwater). I then used the internal mic recording to fill out the treble. Still not 100% satisfied, as people were chattering incessantly like 2 feet from the recorder. Haven’t been able to filter out the chatter without ruining the higher frequencies that are exactly what I’m looking for from that track.

Tonight I’m going to replicate the track, and run the high pass filter at those settings on one version while running a low-pass filter at a few different settings on the other one to see if I can “knock out” the sound. Will report back.

Offline nulldogmas

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Re: Sounds like clipping...but it isn't...
« Reply #16 on: March 21, 2018, 07:26:25 PM »
Sorry, reading back, I get the recording situation more clearly now.

It really does sound like the signal from the turntable is at fault, whether that's due to the turntable output itself or the RCA cables. It's possible you brickwalled, if the recorder's input is more sensitive to bass frequencies, maybe. But either way, you accurately recorded a distorted signal.

If the "crunching" is all in the upper frequencies, you could try the high pass filter on the turntable feed and compensate by cranking up the higher frequencies on the mic recording. How that sounds is going to depend on how much of the audience chatter is in the high frequencies, but it's worth a shot.

Offline rumbleseat

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Re: Sounds like clipping...but it isn't...
« Reply #17 on: March 22, 2018, 10:12:18 AM »
I am now thinking that the DR-40 might have been overloaded by low frequency energy.

There's an ominous statement in the DR-40 Reference Manual on page 38 under "Recording an External Device (LINE-IN)":
http://tascam.com/content/downloads/products/872/e_dr-40_rm_vb.pdf

CAUTION
Reduce the output level of the external audio device if the input sound is distorted even when reducing the input gain level on the unit.
When an external audio device with fixed output line level is connected, it would be impossible to control the gain level appropriately because of excessively large input signals.  In such cases, use the headphone jack or other level-controllable output for connection to the unit.


I looked at the spectrum of the WAV clip and during the worst distortion, there's significant energy down to 20 Hz.  Commercially produced music typically doesn't go that low, but synthesized bass certainly can.  And the the PA system would typically roll off those frequencies so they wouldn't wreak havoc with the power amps and main speakers.

So, I think the solution is to keep the lowest frequencies out of your DR-40.
The DR-40 does have a low-cut option, but apparently it only applies to the mics and not the external inputs - too bad.

Parts Express sells a handy assortment of RCA in-line filters that should do the trick:
https://www.parts-express.com/brand/harrison-labs/265

They've got high pass filters at several cutoff frequencies and I'm thinking the 30 Hz High Pass Filter might work.
https://www.parts-express.com/harrison-labs-fmod-inline-crossover-pair-30-hz-high-pass-rca--266-248

They also have 6 and 12 dB attenuators that could solve this problem.
https://www.parts-express.com/harrison-labs-6-db-rca-line-level-audio-attenuator-pair--266-242
https://www.parts-express.com/harrison-labs-12-db-rca-line-level-audio-attenuator-pair--266-244

I don't have any experience with these devices, so I don't have a guess as to which would work best...

Hope this helps!


AKG C480B CK61 cards >  Canare L-4E6S with Neutrik EMC > Tascam DR-680 MKII > memories

Offline ycoop

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Re: Sounds like clipping...but it isn't...
« Reply #18 on: March 22, 2018, 04:30:00 PM »
Thanks for all the input folks, this has been an informative (though horribly frustrating) process. I came up with something border-line listenable last night by running a high pass filter (600 Hz and 12 dB per octave IIRC) to isolate the bass and filling out the treble from the internal mics. Better than nothing, we’ll see what the DJ thinks. I’ll post a clip tonight. Those RCA attenuators look good if I want to record another one of his sets, which he’s going to be doing every month. Don’t have any budget for recording equipment at the moment (waiting for a few months of delayed paychecks from work).

Interesting that the low pass filter removed the noise though.

Also reading that caution statement has me concerned about the inputs being fried again. Well I guess I’ll see how they fare if I manage to get a patch in to someone’s rig at Ghost Light this weekend.

Thanks again for troubleshooting this with me.

Offline rigpimp

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Re: Sounds like clipping...but it isn't...
« Reply #19 on: March 22, 2018, 05:00:14 PM »
Interesting that the low pass filter removed the noise though.

Are you sure that it was a low pass filter and not a high pass filter?

I have had my Tinybox puke on bass-heavy rap shows.  My results for several were just like what you describe in your OP, crunching distortion but not clipping or brickwalling.  I knew when I could feel the low frequencies vibrating the walls of my digestive system the raw end product was gonna have problems.  Someone here pointed me in the direction of Fabfilter Pro-Q 2 and the problem was solved with a high pass filter and some frequency massaging.

Either way, I am glad that you found approaching the listenable threshold.  Keep playing with it and remember when you are doing repair try little bits at a time and stop.  It is way too easy to get carried away and end up with something really bad.
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Offline 108Ω

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Re: Sounds like clipping...but it isn't...
« Reply #20 on: April 18, 2018, 04:01:33 AM »
Today's lesson may well be that an input level control isn't always a pad. (often not)

A good refresher:
https://support.biamp.com/General/Audio/Gain_structure%3A_input_and_output_levels

Glad to hear that you worked through it!
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Offline ycoop

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Re: Sounds like clipping...but it isn't...
« Reply #21 on: April 18, 2018, 04:29:48 AM »
Funny you replied today, I was just checking back in for a link to those in-line RCA attenuators. I’m thinking about buying a pair of the 12 dB ones. I figured those would be more useful to keep around even if they don’t end up solving the problem.

edit: Forgot to ask this before, but why can I only find RCA attenuators and not 1/4" TRS/TS ones?
« Last Edit: April 18, 2018, 06:18:11 AM by ycoop »

Offline 108Ω

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Re: Sounds like clipping...but it isn't...
« Reply #22 on: April 21, 2018, 02:03:18 AM »
XLR are the common types for Mic level / board connectors
TRS / TS stuff usually a "Direct Box" level control

Resistors may add noise, and even more so if unbalanced, so take a listen at the floor when using them
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