Convert WAV to M4A
Drop a WAV and download an .m4a file carrying AAC audio at 192 kbps. The source sample rate and channel count are preserved.
Encoding once from an uncompressed master is the best case for any lossy codec: the encoder sees the full signal and makes a single set of tradeoffs.
AAC against MP3
At matched bitrates AAC keeps more high-frequency content and handles transients with less smearing than MP3. The gap is small at 256 kbps and obvious at 96 kbps, which is why streaming services and mobile platforms standardized on it.
The cost is compatibility. A decade-old car stereo or a cheap standalone player may read .mp3 and nothing else.
Size
At 192 kbps, expect roughly 1.4 MB per minute regardless of the source sample rate. A 40 MB, 4-minute stereo WAV comes out near 5.5 MB.