Pushing the QA403 to its limits: THD below -142 dB with E1DA Cosmos APU Notch + Victor Oscillator

In this video I show how to dramatically improve THD measurement performance of the QuantAsylum QA403 audio analyser by combining it with the E1DA Cosmos APU Notch filter and the Victor ultra-low-distortion sine wave oscillator. T
his setup consistently achieves THD readings below -142 dB — results that rival professional laboratory-grade equipment at a fraction of the cost.
I also test the older QA400 with the same signal chain, reaching THD = -130 dB on a ten-year-old unit — remarkable for such affordable hardware.
📊 Key results:

QA403 + APU Notch + Victor + 6dB gain: THD = -142.09 dB SNR=-122,6db, THD+N=-122,11db
QA400 + APU Notch + Victor: THD = -130 dB, SNR = -120 dB, THD+N = -119 dB
🔗 Links & Resources:
https://forum.quantasylum.com/t/thd-measurement-lower-than-127-db/2138/11?u=eric
Victor Ultra-Low-Distortion Oscillator: https://viccc42.wixsite.com/uld-audio
Full measurements & discussion on the QuantAsylum forum: https://forum.quantasylum.com/t/thd-measurement-lower-than-127-db/2138/11?u=eric
E1DA Cosmos APU: https://www.e1da.com
QuantAsylum QA403: https://quantasylum.com

Видео Pushing the QA403 to its limits: THD below -142 dB with E1DA Cosmos APU Notch + Victor Oscillator канала Eric Gross ZenViewStudios LAB