Is there a way to view in an oscilloscope (ideally, PC-based and cheap) the carrier signal by itself? With the right tonearm you could micro-adjust the rake angle until the carrier is cleanest and/or loudest (a single, constant signal is easier to monitor).
It's quite easy to judge subcarrier amplitude even from the composite baseband+subcarrier waveform. If you record needle-drops of CD-4 material into a DAW (like the GNU (GPL) Audacity program), you can inspect the subcarrier amplitude with ease. (I've attached a screen shot).
Test recordings of some "dead-wax" (silent grooves) towards the centre of the record are best. If one exists, the inter-track grooves between the last two tracks on a side is very suitable because the subcarrier is always present even when the baseband modulation is silence.
I do wholeheartedly agree that stylus rake angle (SRA) is critical to the best CD-4 replay. Appendix 2 of this page:
http://pspatialaudio.com/vertical_tracking_error.htm
develops a very simple model of the devastating effect upon frequency response if a Shibata/ line-contact stylus is not orthogonal with the groove.
Richard
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