Audio Frequency Modulation (AFM) is an audio recording standard used by Betamax and VHS Hi-Fi stereo, 8mm and Hi8 video systems. AFM is mono on 8mm systems and stereo on Hi8.
References Capelo, Gregory R.; Brenner, Robert C. (1998). "VCR Audio Processing: Theory and Troubleshooting". VCR Troubleshooting & Repair. Newnes. ISBN 978-0-7506-9940-2.