Both managed to convert my AAC recording (from the VoiceRecorder Ap on the Android smart phone) to MP3.
(1) foobar created at 10MB file but reported errors
(2) FFmpeg created a 15MB file and reported no errors
I could not spot a difference between the two MP3 files; both began with mt pulling the door shut on a 15-munute walk and both ended with me pulling my door shut on my return home.
FLAC files may be 8, 16 or 24 bits per sample. 16-bit FLAC are the most common. If the Foobar file is 16-bit and the FFmpeg file is 24-bit, that would account for the size difference. You could check the file formats here: https://mediaarea.net/MediaInfoOnline
Thank you, Steve. That might explain the size difference.
I quoted the sizes with the error in case anyone else was puzzled.
All of this was a major step for me because, until this week, I had not known how to convert (and hence edit, or make use of) an audio file produced by the Android VoiceRecorder ap (Voice Recorder_v3.08_apkpure.com.apk).
Of course, I deleted my test files after the experiment , but I will make two more and test them against MediaInfoOnline.