Bob Cordell said:
http://www.diyaudio.com/forums/showthread.php?s=&postid=1312164&highlight=#post1312164
I have noticed Audacity gives occasional dropouts: I've seen ~100mS gaps with 24/192K on a refurb gateway 2.0 GHz XP home 1 G dram, proabably need to check with 2nd channel digitizing the drive V to see if smaller dropouts aren't ruining the data, maybe slower would work better, need to find settings to optimize cpu performance, maybe ram disk?
the Juli@ does suffer from noise spurs, it looked like the emu 1820m was somewhat better @ ~ US$500, other cards/usb boxes in the prosumer world should be pretty good
mige0,
theoretical noise floor is:
SNR = 6.02N + 1.76dB + 10 log(M/2)
N ..... number of bits of A/D
M .... number of samples in FFT record
For this reason, it is possible to get something like 125-130dB even from 16-bit A/D.
My "noise floor" image was taken with 24-bit, 128K samples.
1Vrms (0dB) is close to max. level, so the narrowband SNR is up to some 140dB in the midband. The higher M (more samples in FFT), the narrower band of noise analysis.
theoretical noise floor is:
SNR = 6.02N + 1.76dB + 10 log(M/2)
N ..... number of bits of A/D
M .... number of samples in FFT record
For this reason, it is possible to get something like 125-130dB even from 16-bit A/D.
My "noise floor" image was taken with 24-bit, 128K samples.
1Vrms (0dB) is close to max. level, so the narrowband SNR is up to some 140dB in the midband. The higher M (more samples in FFT), the narrower band of noise analysis.
Hi
Yeah, with resolution cranked up to 0,17 Hz ( 262144 FFT points implemented in AudioTester due to a feature request of mine some time ago ) it looks really impressive !
Noise floor is down a 150 dB from full scale this way.
Same setup as shown in earlier posts ( done at 4096 FFT points ) but scaled to full scale and average = 5.
The lower noise floor with signal applied is most likely due to the low source impedance of the –60 dB divider of around 50 Ohm compared to the no signal input impedance of around 10 kOhm.
Wonder if that can be topped by earls method ?
Greetings
Michael
PMA said:
Yeah, with resolution cranked up to 0,17 Hz ( 262144 FFT points implemented in AudioTester due to a feature request of mine some time ago ) it looks really impressive !
Noise floor is down a 150 dB from full scale this way.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Same setup as shown in earlier posts ( done at 4096 FFT points ) but scaled to full scale and average = 5.
The lower noise floor with signal applied is most likely due to the low source impedance of the –60 dB divider of around 50 Ohm compared to the no signal input impedance of around 10 kOhm.
Wonder if that can be topped by earls method ?
Greetings
Michael
As promised, I made measurements at low power. Load was 4ohm, power 10mW, 100mW and 1W. I equalized measurements at same peak level, corresponding to lowest power, by means of a voltage divider. Peak level is always declared in plots.
For low powers, there seems to be generator contribution in noise floor modulation. Amplifier itself, wit input shorted, does not show such increase and modulation of noise floor, measured at same sensitivity.
The 1st plot is complete view at all the 3 measurements:
For low powers, there seems to be generator contribution in noise floor modulation. Amplifier itself, wit input shorted, does not show such increase and modulation of noise floor, measured at same sensitivity.
The 1st plot is complete view at all the 3 measurements:
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Very interesting.
Well, i should be easy to distinguish generator effects from generator+amp effects, by measuring
- generator by itself into some input impedance similar to the amp's
- generator into the amp, signal off
Because it could also be the amp's reaction to generator input.
PMA said:
Well, i should be easy to distinguish generator effects from generator+amp effects, by measuring
- generator by itself into some input impedance similar to the amp's
- generator into the amp, signal off
Because it could also be the amp's reaction to generator input.
I am sorry but I made a fatal mistakes in the PM-AB1 measurements (posts no. 153,4 and 5). I forgot to switch on power supply of the LP active filter behind the generator, so all the distortion was from that.
Hereby the corrected image. You can see again modulated noise floor, this results from the active filter.
Hereby the corrected image. You can see again modulated noise floor, this results from the active filter.
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