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Old 4th April 2012, 08:20 PM   #21
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Quote:
Originally Posted by studiostevus View Post
This is 19+20Khz 1:1 on my NOS TDA1541a.... to be honest, I don't really know what I am (supposed to be) looking at.... enlighted me..
What I was looking for is the "grass" that is present in-band and also out-band, past the 20kHz mark.

For PCM61 the higest off-band alias apears at -84dB, for TDA1541 at -70dB (worse), for PCM1791 at some -110dB (best).
In-band I have some "grass" between the spectrum at noise floor level.
You have two huge off-band spikes mirrored around the 22.05kHz and you have a lot of in-band "grass" that rises numerous times to -80dB (don't know what the averaged total would end up). That is distortion of the original signal.

Now... What I don't know is why you don't have any beats between the fundamentals in your signal. What ADC are you using?

Last edited by SoNic_real_one; 4th April 2012 at 08:26 PM.
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Old 4th April 2012, 11:26 PM   #22
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I redid my measurements with different setup for the ballanced inputs (to accept unballanced signal). No change.
Loopback E-MU1820m, PCM61@0dB, PCM61@-60dB, PCM61@19+20kHz@-3dB. I still don't get what's up with the beats...
Attached Images
File Type: png EMU1820m_loopback.PNG (69.7 KB, 391 views)
File Type: png PCM61_0.PNG (71.5 KB, 120 views)
File Type: png PCM61_60.PNG (64.4 KB, 117 views)
File Type: png PCM61_19+20_0dB.PNG (63.3 KB, 114 views)

Last edited by SoNic_real_one; 4th April 2012 at 11:52 PM.
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Old 4th April 2012, 11:40 PM   #23
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Same measurements for TDA1541@0dB, TDA1541@-60dB, TDA1541@19+20kHz/-3dB. Same OpAmp (LM4562) as PMC61.
Attached Images
File Type: png TDA1541_0.PNG (86.1 KB, 114 views)
File Type: png TDA1541_60.PNG (89.1 KB, 27 views)
File Type: png TDA1541_19+20_0dB.PNG (89.7 KB, 22 views)
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Old 4th April 2012, 11:48 PM   #24
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And for PCM1791@0dB, PCM1791@-60dB, PCM1791@19+20kHz/-3dB.
Attached Images
File Type: png PCM1791_0.PNG (85.9 KB, 33 views)
File Type: png PCM1791_60.PNG (83.1 KB, 27 views)
File Type: png PCM1791_19+20_0dB.PNG (75.8 KB, 20 views)
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Old 5th April 2012, 12:30 AM   #25
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Hi,

Quote:
Originally Posted by studiostevus View Post
LPF... How? Where? In Arta?
In the signal. Generate a test signal, for example using Audacity etc...

Ciao T
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Old 5th April 2012, 10:34 PM   #26
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Quote:
Originally Posted by SoNic_real_one View Post
I redid my measurements with different setup for the ballanced inputs (to accept unballanced signal). No change.
Loopback E-MU1820m, PCM61@0dB, PCM61@-60dB, PCM61@19+20kHz@-3dB. I still don't get what's up with the beats...
For -60 dB, did you adjust the MSB ?
You can do it using a headphone, adjusting for most pure tone
and watching the live measurement, grass sinking in the noise floor.
Also try other pcm61 chips, you may find better ones.
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Old 6th April 2012, 12:24 AM   #27
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I did ajust the MSB, it did affect the 2nd harmonic the most. Maybe I can redo the adjustment now, with the better card.
I have (6) PCM61 but didn't really had time to rotate them. I was thinking to parallel them when I am bored
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