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Old 8th December 2016, 06:49 AM   #1
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Default Hearing strange distortions

I have a es9018 based multichannel DAC connected to Hypex Ncore400 and UcD400 amps. The interconnection is balanced.

This is used in a DSP active 4way

I notice strange scratchy, crackling, distortion almost modulating with the music, when i just play the bass channels with mid/tweeter muted.

Bass is two seas excel W22 8" drivers in parallel for a 4ohm load.

Bass is bandpassed in the range 60Hz to 300Hz using LR4 slopes.

I do notice the same distortion with all my DSP bypassed and running some bass tones directly from another software player. So this is not an issue with the DSP.

The DAC itself measures clean in distortion checks using a spectrum analyzer.
But replacing the DAC with a motu/focusrite DAC in the same configuration gets rid of the distortion.

Here are some samples.
https://drive.google.com/open?id=0B7...UowV21JeU5BSWM

The distortion/noise seems to be some higher frequency components as they are audible only on-axis with the drivers. They are audible at nominal listening levels even from about 1m straight in front of the drivers.

Please give them a listen and advice.

Last edited by diyaudnut; 8th December 2016 at 06:51 AM.
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Old 8th December 2016, 11:10 AM   #2
fluid is offline fluid  Australia
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Do you have a passive speaker or a headphone amp that you can listen to the individual channels of the ES9018 to see if they are all affected the same way if used with full range signals?

Are you able to use ARTA or rightmark to see what is coming out of the DAC when you play a test tone?

If you can do either of those it will probably help to narrow down what the issue could be.
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Old 8th December 2016, 04:30 PM   #3
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Thanks Fluid.

Its not audible in presence of full range signal.
Headphone amp is a good suggestion, i dont have one, but will try to get that tested.

When tested on Spectraplus with a EMU0404 USB soundcard, the distortions seem to be below -100db
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Old 8th December 2016, 04:41 PM   #4
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And all channels produce this distortion when fed bass only.
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Old 9th December 2016, 01:30 AM   #5
fluid is offline fluid  Australia
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Strange that the distortion is not audible with a full range signal perhaps it is an interaction between the DSP processing and the DAC.
When you say full range signal how are you testing that? If you can use two channels of the DAC to a separate pair of passive speakers or headphone amp and have no issues then you have eliminated the DAC as being inherently faulty.

Any distortion at -100dB would be very difficult to hear at all. What I hear in your videos sounds much louder than that.

It sounds as if something is being clipped slightly, are you able to monitor the gains throughout your signal chain in some way?

Try some test tones at different frequencies through spectraplus it may be that one frequency in particular is resonating or clipping, it is hard to isolate with music as a test signal.

Last edited by fluid; 9th December 2016 at 01:34 AM.
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Old 9th December 2016, 05:49 AM   #6
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fluid

It is unlikely a DSP issue.

I tested the DAC with everything in the chain completely bypassed. That is no DSP no Jriver and the distortion is still present.

For example i tired REW output directly though the DAC driver and i reproduced the issue.

In full range i think the distortion is hidden away by mid/tweeter sound. Carefully listening close to the bass driver still reveals the distortion being present.
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Old 9th December 2016, 05:52 AM   #7
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could you explain the clipping thought.

This sounds like some high freq noise getting modulated by the music.
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Old 9th December 2016, 06:28 AM   #8
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Quote:
Originally Posted by fluid View Post
Strange that the distortion is not audible with a full range signal perhaps it is an interaction between the DSP processing and the DAC.
When you say full range signal how are you testing that? If you can use two channels of the DAC to a separate pair of passive speakers or headphone amp and have no issues then you have eliminated the DAC as being inherently faulty.

Any distortion at -100dB would be very difficult to hear at all. What I hear in your videos sounds much louder than that.

It sounds as if something is being clipped slightly, are you able to monitor the gains throughout your signal chain in some way?

Try some test tones at different frequencies through spectraplus it may be that one frequency in particular is resonating or clipping, it is hard to isolate with music as a test signal.
Fluid, with a passive speaker, I think the noise will get filtered out by the LP on the bass driver. It is not really audible mixed with mid/tweeter.
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Old 9th December 2016, 06:29 AM   #9
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Everything currently points to the DAC as a Motu and Foucsrite DAC in the same system doesnt produce the distortion.
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Old 9th December 2016, 06:33 AM   #10
fluid is offline fluid  Australia
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Quote:
Its not audible in presence of full range signal.
Maybe I misunderstood what you wrote before.

To me the only way to test if the DAC alone has the issue is to isolate it. Use it just by itself straight from your source into an amplifier and into a speaker. If you have a passive speaker or headphone setup that makes it easier if not then use the speaker that covers the widest range which may be your mid driver.

If you get the same distortion then you know the issue is coming from the DAC. Run some test tones through the DAC and see what comes out, that will help to identify what is being distorted.

I don't see how high frequency noise would be modulated by the music signal. When the distortion coincides with a musical event it is often that a peak in the music is causing clipping or overloading somewhere in the chain.

When using DSP there is opportunity to cut and boost and sometimes this can cause one of the stages to clip. If you have completely bypassed any processing then you should be able to rule that out as a cause.

Digital clipping is a very horrible crunching noise which does not sound like your video. I have a DSP based active system and have heard the DSP clipping it is fairly unmistakeable, your's sounds more analogue in nature.

Depending on the voltage output of the DAC it could be causing clipping in your amp although that would likely make it very loud. Without knowing more about the equipment you are using it is hard to guess what might be going wrong.

Is the DAC a commercial unit or DIY? Has it ever worked properly just as a stereo DAC or is this the first time you are testing?
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