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A 10-bit ADC chip and a Raspi zero together cost under $10 on Adafruit. You would sidestep the audio card altogether.

or one of those even cheaper 16bit USB soundcards https://github.com/ozel/DIY_particle_detector/wiki/Soundcard... I believe Steve (who wrote the blog) might have had the wrong cable for his other computer (3-pin vs. 4-pin 3.5 mm jack)