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What is causing this weird noise at the end of a sweep ?

post #1 of 7
Thread Starter 

Dear friends,

I have found and put into practice a little plugin script for Audacity to generate tone sweeps.

 

Whether I listen this from my iMac->headphone out->little H/K speakers

 

or

 

iMac->USB->ODAC->O2->Sennheiser HD600

 

I hear the same "artifacts" if played with Audacity or VLC:

 

Approx. from 1.5 to 3-5 seconds I'd describe the sound as oscillating from left to right

 

Approx. from 8.5 seconds onwards the frequency sweep is also piggybacked by apparently random oscillations similar to old radios being tuned.

 

What's happening ?

 

I am not hearing these artifacts if I play the same file via Audirvana or even if I drag and drop it on the browser

 

Here is the file: http://www.filedropper.com/sweep

 

Thanks a lot

post #2 of 7

Have you tried other sweep signals (google returns few good ones)?

post #3 of 7
Thread Starter 

WOW lol yes :-) Laughing since I had the volume a bit high on the speakers and played a 20-20K sweep from here http://www.wavtones.com/functiongenerator.php and my doors rattled at the low end startling me :-) Yes when the frequency goes up high I experience these weird "parasounds" ... no clue.

post #4 of 7
Thread Starter 

And thanks a lot for trying to help :-)

post #5 of 7
Quote:
Originally Posted by rjalex View Post
 

And thanks a lot for trying to help :-)

 

 

Did I ?

 

This may be caused by poor SRC.

 

I didn't check the audio you linked (I don't want to install aiff compatible software just to check this) nor the Mac audio system so, My next Q's are

 

1. Are you using CD audio quality sweep

2. Does the issue happen when sweep is done using 48kHz


Edited by jiiteepee - 1/7/14 at 8:20am
post #6 of 7
Thread Starter 

Ok I think I have interesting results.

 

It seems it's an aliasing problem and shows why using a good player like Audirvana DOES make a difference.

 

Here's a great web page to test:

 

http://www.audiocheck.net/audiotests_aliasing.php

 

If I play both the 44.1 or the 48KHz sweeps in my browser, even reproducing them with my ODAC+O2 I get a LOT of aliasing !!!

 

If I DLd the same files and play them with Audirvana the sweeps are perfectly the way they should.

 

Didn't quite get the math behind this LOL but I understand it's Mr. Nyquist fault ! :-)

 

If you have a dumbproof explanation, I'd love to hear.

 

Take care

post #7 of 7

Yes, just blame Nyquist ... ;)

 

Audirvana has a build-in digital filter for to remove unneeded frequencies?

 

You could use Audacity for to demonstrate this what happens when you apply a digital filter which removes those un-needed frequencies. Does the aliasing issue become fixed.

 

(Is it the hardware or the software which is poorly designed? )

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