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It contains two copies of an image file. If there are bit errors, then you'll see some of the pixels change from the first copy to the second - I see this when the volume is outside the reliable range.
Let me know failure/success, what kind of Apple you have, what your sound output device is, and what range of volumes seem to work.
I got your wave file to load. Took about 5 seconds, counting 1-1000, 2-1000, etc. Final result: a hi-res picture of random dots/dashes of colors/white/black. I did not see two pictures, or if I did, I did not see a change from one to the other, IIRC, but I was not watching very closely.
I used an audio cable from my Lenovo PC to my Enhanced Apple //e. I extracted the 23k_test.wav file from 23k_test.zip using 7-zip. Played the 23k_test.wav file using (default) Windows Media Player. Speaker volume was set to 50% with no enhancements. [This is the same volume that I used to bootstrap ADT ProDOS.]
I had to turn off my Apple //e to get out from under your program and then turn it back on to park my Sider HDD heads. My Apple //e kept dropping into the monitor after escaping your program instead of cold/warm starting when I pressed ctrl+reset or ctrl+apple+reset.
I think it might be easier to see changes if you had two pictures of real things that are different from each other but very recognizable (like your "mug shot," front and profile, with a placard numbered one and two [ ;-) & )-; ], LOL). Then, if there were errors, they would not look as good (as you), full of holes (random dots/dashes of colors/white/black). You could show each picture for a few seconds each, repeatedly until escape is pressed, then exit to Applesoft/Integer BASIC via the cold start entry vector ($E000). [That is what I had to do after booting up ProDOS/ProSel and dropping into Applesoft, then into the Monitor ( ]Call-155 then *E000G ) before I could LOAD successfully. Later, I realized that all I really had to do was to turn off my Sider before turning on my Apple //e.]