// MODULE 4 OF 8 · SBE CPT PREP v1.0
A file is a promise about what the air will sound like.
Sampling
CONVERSIONAnalog becomes digital by sampling. Nyquist: sample rate must be at least 2× the highest frequency — hence 44.1 kHz covers hearing. Broadcast plants run 44.1/48 kHz. Bit depth sets dynamic range: ~6 dB per bit — 16-bit ≈ 96 dB, 24-bit ≈ 144 dB working room.
Formats
FILESWAV/AIFF — uncompressed masters. FLAC — lossless compression. MP3/AAC — lossy: discards audio to shrink; fine for delivery, never as an editing master, and never re-encode lossy-to-lossy more than you must. Streaming default on the network: MP3/AAC mounts at 128–320 kbps.
Metadata
THE PART EVERYONE SKIPSID3 tags carry artist, title and embedded art. When a file has no embedded art, AzuraCast serves the generic station badge — which is exactly why Recent Plays used to show the U-Rock badge instead of band photos until profile photos were wired in as the fallback. Clean metadata = clean now-playing, clean charts, clean royalty logs.
On the U-Rock rails
NETWORK TIE-INMedia Library ingest probes duration with ffprobe and infers category (a 5-second WAV named 99-track-99 is an effect, not a Station ID; a 5-minute 'Artist - Title' is music). Feed the machine clean names and tags and it stays clean.
Do this now
HANDS ON- Tag one music file completely: artist, title, album, year, embedded art.
- Explain why you never 'upgrade' a 128 kbps MP3 by re-exporting it at 320.