In my initial observations of the first laptop (IBM Thinkpad T60) the laptop provided a clean audio signal from 0hz and above up until a week ago that signal became noisy which was fixed by using a different laptop (Panasonic CF-29) that has grounding.
Noisy Signal with Thinkpad T60, ungrounded:
Clean signal with grounded Panasonic CF-29:
Tests dB vs Hz
- Anomalous under 100hz:
2. Anomalous above 100hz:
To be continued….