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| Question: Cheap pure sine wave genertor 1khz? |
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| Vovk_Z:
--- Quote from: MasterT on January 11, 2020, 04:02:09 am --- --- Quote from: innkeeper on January 11, 2020, 03:13:46 am ---i've hit up victor from the diyaudio forum to see if he has any of his boards available. he is getting better then -150 Db. --- End quote --- What circuits? I've seen link to e-b https://www.ebay.com/itm/Low-Distortion-Audio-Range-Oscillator-1KHz-Sine-Wave-Signal-Generator-PCB-Board/262844562138, let's call it JFET-Wein, description says: --- Quote ---Low distortion coefficient of the sinusoidal oscillator circuit board, oscillation frequency: 1KHz, low distortion, distortion factor 0.0064% (- 124dB) --- End quote --- --- End quote --- - this one isn't Victor's, it's unnamed RC-oscillator. It really have 0.006%, but have a potential to go to 0.001% with smal change (resistor "120-150k" change to value 27-30k if I'm not wrong). Best side of it that it is variable frequency with stable amplitude. Victor's oscillator is constant frequency and ultra low distortion. |
| f5r5e5d:
much work on ADC/DAC THD cancellation: https://www.diyaudio.com/forums/equipment-and-tools/328871-digital-distortion-compensation-measurement-setup.html |
| MasterT:
--- Quote from: trobbins on January 13, 2020, 10:41:02 pm --- --- Quote from: MasterT on January 13, 2020, 10:00:47 pm ---This trick IS limited by performance of the adc. --- End quote --- ... Noise level will depend on a few factors, so not straightforward to report on. The mid-band noise level for that EMU soundcard is down around -130dB from full-scale signal, and uses 24-bit 192 kHz AKM AK5385A ADC and AK4396 DAC. --- End quote --- Dreams, dreams... Based on a DS from this http://www.datasheetcatalog.com/datasheets_pdf/A/K/5/3/AK5385A.shtml THD of the appointed ADC is -103 dBc. Period. Nothing could be measured below this level. More than that, depends on a driver analog front end , likely results never cross -100dB . I see here https://www.soundonsound.com/reviews/emu-0404 they honestly print 0.001% THD+N. No where close to -130dB. |
| rhb:
Unless I were prepared to launch into a serious development project, I'd use a sound card. Write .WAV files covering the test amplitudes and frequencies. Play them back through the sound card. Record L->L, L->R, R->L & R->R Solve for the input and output errors of each channel and correct. At each frequency and amplitude there are 4 equations and 4 unknowns. You can get almost arbitrary accuracy via signal processing with large datasets. Otherwise, I'd recommend building a single frequency version of Jim Williams last version from "Max Wien, Mr. Hewlett and a Rainy Sunday Afternoon" using well matched fixed parts. But then you have to design and test the distortion analyzer. Having lived through the THD wars in audio gear in the late 70's I feel obliged to point out that the distortion of the best sound transducers (microphone and speaker) are an order of magnitude larger than a cheap audio IC. Have Fun! Reg |
| MasterT:
--- Quote from: rhb on January 14, 2020, 03:10:20 am ---... Record L->L, L->R, R->L & R->R Solve for the input and output errors of each channel and correct. At each frequency and amplitude there are 4 equations and 4 unknowns. You can get almost arbitrary accuracy via signal processing with large datasets. --- End quote --- No, you can't. The issue is that harmonic's magnitude & phase (thd-n) are not constants. Doesn't matter how big data sets are, how accurate equation written or what precision of the floating math. The data becomes a junk after a few milliseconds, because ADC is drifted, always changing - there is no single static constant magnitude & phase below -100 dBc with audio ADC, or -110 with precise SAR. Same with a DAC. During debugging my project, I came to conclusion that uCPU has to continuously monitor each thd-n and make adjustment "on the fly" . Calibration & look-up table doesn't work, actually it does for stm32f767 internal 12-bits DAC with initial start-up thd-3 about -70 dBc, LUT could fix this value to -95/-100, but than magic show begins. |
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