The wider channels is the source of the available audio fidelity, but wider channels make you more exposed to noise, not less.
From a signal:noise perspective, what matters is the ratio of bandwidth available in the transmission channel to the bandwidth of the content you are trying to send. Consider GPS, for instance, where the use of a 2 MHz channel to send 50 bps data provides an SNR advantage that would otherwise be achievable only through witchcraft.
FM has strong noise immunity advantages -- notably AM rejection and the capture effect -- but they don't provide additional sound quality by themselves. That's where the bandwidth helps. An FM channel that is only as wide as an AM channel would sound pretty awful.
> FM has strong noise immunity advantages -- notably AM rejection and the capture effect -- but they don't provide additional sound quality by themselves. That's where the bandwidth helps. An FM channel that is only as wide as an AM channel would sound pretty awful.
Comparing such low-modulation factor FM with traditional AM would be an interesting experiment.
It certainly wouldn't sound good, but I'm not sure it would sound worse than traditional AM at the same SNR. The NFM use-cases I'm familiar with tend to cap audio bandwidth, so they're not fair comparisons.
I'm mostly imagining what music would sound like via NBFM on a VHF amateur or public-safety radio channel. It's not an appealing thought... the words "toll quality" come to mind.
From a signal:noise perspective, what matters is the ratio of bandwidth available in the transmission channel to the bandwidth of the content you are trying to send. Consider GPS, for instance, where the use of a 2 MHz channel to send 50 bps data provides an SNR advantage that would otherwise be achievable only through witchcraft.
FM has strong noise immunity advantages -- notably AM rejection and the capture effect -- but they don't provide additional sound quality by themselves. That's where the bandwidth helps. An FM channel that is only as wide as an AM channel would sound pretty awful.