Measuring ClassD with Audigy 2 Value

Pafi · 22nd June 2010, 08:50 AM

I bought an Audigy 2 Value (SB0400) for measuring ClassD amplifiers, and there is a strange thing: on output I see a high freq noise with quite high amplitude (80 mV). It's spread between 60 and 300 kHz. Is it normal? Would anybody check his/her similar soundcard?

savu · 23rd June 2010, 07:40 PM

Hello Pafi ...
I have Audigy 2 ZS paltinume edition or something like that.
What is the name of the software u use for FFT with the soundcard?

Regards,

Pafi · 24th June 2010, 10:24 AM

Hello!

Yesterday I measured on an other card, EMU1212, and it has the same issue, so it's not unique.

I measured it with oscilloscope. FFT is not neccessary, however useful. You can't check the sound card with itself, since there is a low pass filter on input with ~40 kHz corner freq.

81bas · 24th June 2010, 02:57 PM

Did you measured EMU1212 in the same your computer? maybe it is an PSU or motherboard issue, which produces such "side effect"?

Pafi · 24th June 2010, 03:34 PM

Quote:

Did you measured EMU1212 in the same your computer?

No, it was an other PC. It cannot come from the PSU, because it's not periodic at all, and it's present only on the output of sound card. And too strong to be a PSU (or motherboard) noise. And the motherboard noise would be audible, but this isn't.

81bas · 24th June 2010, 05:04 PM

I heard, some audio cards are using so called 'jack sensing' feature, to determine, what was plugged in - microphone or headphones, etc... Maybe this does produces such a problem? Is this HF signal presented at the card output all the time during PC startup? Is this noise present during playback of some track at low volume level?
Very interesting problem

Pafi · 24th June 2010, 10:58 PM

Quote:

Maybe this does produces such a problem?

No. This problem is due to the nature of sigma-delta converters. All sigma-delta converters has more or less out of band noise, while in band noise is suppressed by a so-called noise shaping. Out of band noise is suppressed by analog filter, but since in this case the pass-band is wide, it can't be filtered out as good as in a low sampling rate DAC. Also the oversampling ratio is lower, what makes the situation worse.

SoNic_real_one · 25th June 2010, 12:15 AM

Maybe, but NOT at this level! He is talking about 80mV form a total of 2000mV. That is some 28dB! What DAC has this level of noise?

fehrudi · 25th June 2010, 04:56 AM

For example CS4392 (EMU0202).

AP2 · 25th June 2010, 08:09 AM

Hi,
when measure output noise what is parameters (samples/sec)?
I know Audigy 2,flat-108dB up to 46KHz.
noise have relation with samples/S (non linear) because board use multiplier clock divisor . plus dac not professional.

22nd June 2010, 08:50 AM	#1
Pafi diyAudio Member Join Date: May 2004 Location: Budapest	Measuring ClassD with Audigy 2 Value I bought an Audigy 2 Value (SB0400) for measuring ClassD amplifiers, and there is a strange thing: on output I see a high freq noise with quite high amplitude (80 mV). It's spread between 60 and 300 kHz. Is it normal? Would anybody check his/her similar soundcard?

23rd June 2010, 07:40 PM	#2
savu diyAudio Member Join Date: Feb 2007 Location: Cluj - Napoca	Hello Pafi ... I have Audigy 2 ZS paltinume edition or something like that. What is the name of the software u use for FFT with the soundcard? Regards, __________________ 1'st rule of chess: The only way to get smarter is by playing a smarter opponent.

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24th June 2010, 10:24 AM	#3
Pafi diyAudio Member Join Date: May 2004 Location: Budapest	Hello! Yesterday I measured on an other card, EMU1212, and it has the same issue, so it's not unique. I measured it with oscilloscope. FFT is not neccessary, however useful. You can't check the sound card with itself, since there is a low pass filter on input with ~40 kHz corner freq.

24th June 2010, 02:57 PM	#4
81bas diyAudio Member Join Date: Jan 2006 Location: Kiel	Did you measured EMU1212 in the same your computer? maybe it is an PSU or motherboard issue, which produces such "side effect"?

24th June 2010, 05:04 PM	#6
81bas diyAudio Member Join Date: Jan 2006 Location: Kiel	I heard, some audio cards are using so called 'jack sensing' feature, to determine, what was plugged in - microphone or headphones, etc... Maybe this does produces such a problem? Is this HF signal presented at the card output all the time during PC startup? Is this noise present during playback of some track at low volume level? Very interesting problem

25th June 2010, 12:15 AM	#8
SoNic_real_one diyAudio Member Join Date: Jan 2008 Location: Virginia	Maybe, but NOT at this level! He is talking about 80mV form a total of 2000mV. That is some 28dB! What DAC has this level of noise?

25th June 2010, 04:56 AM	#9
fehrudi diyAudio Member Join Date: Aug 2004 Location: Hungary	For example CS4392 (EMU0202).

25th June 2010, 08:09 AM	#10
AP2 diyAudio Member Join Date: Dec 2009 Location: Italy	Hi, when measure output noise what is parameters (samples/sec)? I know Audigy 2,flat-108dB up to 46KHz. noise have relation with samples/S (non linear) because board use multiplier clock divisor . plus dac not professional.

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