This was a response to a discussion in the Discord; I realized after I posted it that it is in fact a valuable collection of resources for anyone wanting to tune up a cassette deck after doing repairs and realizing they needed to adjust/verify transport speed, wow/flutter, azimuth, etc so I'm reposting here for posterity:
I recently did a bit of a deep dive into this aspect of cassette deck service; the TapeHeads community have been at this for quite a while. Alan Freed has developed a bit of software that allows anyone to do this easily in their home lab; the video above is a good primer on what and how.
For playback speed and W/F you will need a Sony WS-48B 3KHz tone or equivalent test tape from a reputable supplier; these range in price from ~$20 to over $100 depending on hype and equipment used. Typical tapes found on eBay, etc will be made from a digital source and recorded on a normal bias tape using a supposedly calibrated Nak Dragon or similar deck; this is more than sufficient for most consumer playback adjustment.
Alex Nitikin is widely well-regarded in the community as very knowledgeable; he makes studio-standard calibration tapes using a full-track Revox cassette deck as most of these tapes are supposed to be made. Here is his site; it contains the WFGUI software DL and several other useful links:
http://www.ant-audio.co.uk/index.php?ca ... ry=library
http://www.ant-audio.co.uk/index.php?ca ... ment_tapes
His tapes are a bit more expensive, as you might guess; according to this thread at Tapeheads.net, as of October 2024 his azimuth tape is ~50 quid, while his combination tape is ~80 quid:
https://www.tapeheads.net/threads/a-n-t ... ss.109204/
This article covers the once commonly-available "standard" test/cal tapes and what they were/did:
https://www.petervis.com/Vintage%20Misc ... sette.html
Cheers!