Match the encode to the bandwidth the station and receiver actually delivered
Source-aware MP3 settings for AM and medium-wave recordings, from wide-band 10 kHz captures to typical 5–7 kHz receiver recordings.
MP3 Settings for AM and Medium-Wave Radio Recordings
AM bandwidth varies by era, station and receiver
Modern North American analogue AM transmission standards specify a 10 kHz audio bandwidth, but historical practice and real receivers vary considerably. NRSC guidance notes that many consumer receivers are limited to about 5 kHz or less, and broadcasters have also used narrower 5–7 kHz bandwidths to reduce adjacent-channel interference.
Measure the recording you actually have
An AM recording taken from a narrow portable receiver is very different from a wide-band off-air recording made with a specialist tuner. Do not automatically apply a 10 kHz low-pass merely because the transmitter standard permits it. Look at the spectrum and listen for the point where programme information gives way to receiver noise and adjacent-channel energy.
| Observed source | Starting low-pass | Comment |
|---|---|---|
| Wide-band AM capture | 9–10 kHz | Preserves unusually good AM fidelity. |
| Typical receiver recording | 5–7 kHz | Often closer to the bandwidth real listeners received. |
| Communications / poor archive source | 3–5 kHz | Use only when the programme itself is already that restricted. |
Example commands
lame.exe --abr 128 --lowpass 10 am-wideband.wav am-wideband.mp3lame.exe -m m --abr 80 --lowpass 6 am-archive.wav am-archive.mp3Mono is appropriate when the recording contains no useful stereo information. Preserve stereo if the capture itself includes meaningful stereo ambience, processing or later production.
Standards context
NRSC-1-C specifies a 10 kHz analogue AM transmission bandwidth with a defined stopband above it. NRSC guidance also documents the long-standing use of narrower bandwidths and the limited high-frequency response of many consumer receivers.