# why does AM radio music sound different than FM? **URL:** \ **Category:** Factual Questions\ **Created:** [August 16, 2005, 10:05am UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246 "2005-08-16T10:05:03Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [August 16, 2005, 10:05am UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/1 "2005-08-16T10:05:03Z")
FM music sounds clearer (as I understand that it doesn’t have so much intereference). But it also sounds brighter. I suspect that the AM radio is filtering out some of the higher frequencies or distorting them? ---
**Author:** ![Thin\_Lizzy](https://avatars.discourse-cdn.com/v4/letter/t/e9a140/32.png) [@Thin\_Lizzy](https://boards.straightdope.com/u/Thin_Lizzy)\ **Post date:** [August 16, 2005, 10:10am UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/2 "2005-08-16T10:10:58Z")
I think am is in mono, fm is stereo. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [August 16, 2005, 10:29am UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/3 "2005-08-16T10:29:20Z")
Yes. It doesn’t have to be, but FM is traditionally broadcast in stereo. The downside of FM is that it doesn’t have as good a range as AM. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [August 16, 2005, 10:37am UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/4 "2005-08-16T10:37:27Z")
I dont think that is the whole difference as it is also apparent when heard on mono or through my trani which only has one speaker. The stereo would certainly have an effect though ---
**Author:** ![F.U.Shakespeare](https://avatars.discourse-cdn.com/v4/letter/f/aca169/32.png) [@F.U.Shakespeare](https://boards.straightdope.com/u/F.U.Shakespeare)\ **Post date:** [August 16, 2005, 11:02am UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/5 "2005-08-16T11:02:07Z")
FM channels also have a wider bandwidth than AM channels. This means that FM contains higher frequencies that AM doesn’t. This is separate from the lack of static on FM, which is due to the modulation method (Frequency Modulation vs. Amplitude Modulation) – FM encodes the sound using variations in the radio wave’s frequency, which isn’t affected by interference the way the wave’s amplitude is. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [August 16, 2005, 2:11pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/6 "2005-08-16T14:11:46Z")
The mono versus stereo actually makes zero difference in why FM sounds brighter - it’s the bandwidth as Mr. Shakespeare noted. AM is band-limited to 5 kHz, barely more than a long-distance phone connection. FM transmits pretty much the whole frequency range your ear can hear. The human voice doesn’t use much of the higher frequencies, so voice sounds just fine over AM. Music on the other hand has more high-frequency content, so FM makes a big difference. A bunch of years ago, they came out with “AM Stereo,” apparently because some people believed that the difference in sound quality was due to stereo vs. mono. It wasn’t popular because it still sounded crappy. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [August 16, 2005, 2:13pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/7 "2005-08-16T14:13:38Z")
> [@F. U. Shakespeare](#): > > This is separate from the lack of static on FM, which is due to the modulation method That’s a big part, and another factor is that there is less electrical noise from motors, etc., up around 100 MHz than there is around 1 MHz where AM operates. ---
**Author:** ![bordelond](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bordelond/32/150_2.png) [@bordelond](https://boards.straightdope.com/u/bordelond)\ **Post date:** [August 16, 2005, 2:20pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/8 "2005-08-16T14:20:59Z")
> [@F. U. Shakespeare](#): > > This is separate from the lack of static on FM, which is due to the modulation method (Frequency Modulation vs. Amplitude Modulation) – FM encodes the sound using variations in the radio wave’s frequency, which isn’t affected by interference the way the wave’s amplitude is. Is this also why you can pick up FM radio in a parking garage, but not AM? ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [August 16, 2005, 2:59pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/9 "2005-08-16T14:59:54Z")
> [@bordelond](#): > > Is this also why you can pick up FM radio in a parking garage, but not AM? This might have more to do with the frequencies being used than the modulation. Basically, FM sounds better than AM for three reasons: [ul] [li] **FM is better technology.** Specifically, it’s more noise-resistant: With AM, anything noise on the frequency will be audible to the person listening to the signal, whereas FM is much more resistant to ambient radiation.[/li][li] **FM is on a clearer wavelength.** CurtC touches on this: There’s simply less noise, especially from things that aren’t meant to transmit a real signal, in the higher frequencies. (Up to a point, of course.)[/li][li] **FM stations have more bandwidth.** An FM signal simply has more information packed into it than an AM signal does, and not just because most FM is stereo and most AM is mono. This extra information translates to extra sound quality.[/li][/ul]Of course, two of those three points are due solely to FCC regulations and have nothing to do with AM technology as such. If AM stations had clearance to use the same frequencies and the same kind of bandwidth currently allocated to FM stations, I’m sure we’d hear better AM signals. There’s even a stereo AM standard in existence, but I don’t know of any modern stereo AM stations, or if modern radios can even take advantage of such a thing. There are plenty of people who actually know about this stuff, or know it better than I do. They can expand or correct my points above, but I do think I’ve hit all of the relevant ones. ---
**Author:** ![F.U.Shakespeare](https://avatars.discourse-cdn.com/v4/letter/f/aca169/32.png) [@F.U.Shakespeare](https://boards.straightdope.com/u/F.U.Shakespeare)\ **Post date:** [August 16, 2005, 4:32pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/10 "2005-08-16T16:32:29Z")
> [@bordelond](#): > > Is this also why you can pick up FM radio in a parking garage, but not AM? Derleth is right – the higher frequencies used by FM result in shorter wavelengths (on the order of 3 meters), which penetrate further into apertures than the larger (175-566 meters) AM wavelengths. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [August 16, 2005, 5:26pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/11 "2005-08-16T17:26:14Z")
> [@CurtC](#): > > The mono versus stereo actually makes zero difference in why FM sounds brighter - it’s the bandwidth as Mr. Shakespeare noted. AM is band-limited to 5 kHz, barely more than a long-distance phone connection. FM transmits pretty much the whole frequency range your ear can hear. 5Khz is correct for AM. FM baseband is limited to 12 Khz, so you still lose most of the top octave of human hearing range…but a lot of what is up there is not very “musical”. A violin, for example might sound better, as a lot of the scraping noise of the bow on the strings will be lost. Note that these bandwidth differences are historic, and leagle, not technical limitations. Television video is broadcast as AM, with approximatly 10X the bandwidth of an AM radio signal. (Interestingly, TV audio is FM) There is also Narrowband-FM used by, among others, police and buisness band radio FM also has a property of rejecting interference…known as "capture effect. Not only of atmospheric static, but also distant stations. The FM band is high enough, that it is rare for propagation beyond line-of-sight to occur, but if it does, you’ll still only hear the strongest station. With AM you hear everything mixed togethor. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [August 17, 2005, 3:10pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/12 "2005-08-17T15:10:39Z")
tx for the replies. Was the 5 kHz bandwidth chosen to cram more stations in the AM band? Or perhaps early recievers/speakers couldn’t handle any more? ---
**Author:** ![rfgdxm](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rfgdxm](https://boards.straightdope.com/u/rfgdxm)\ **Post date:** [August 17, 2005, 3:33pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/13 "2005-08-17T15:33:39Z")
> [@scm1001](#): > > tx for the replies. Was the 5 kHz bandwidth chosen to cram more stations in the AM band? Or perhaps early recievers/speakers couldn’t handle any more? To cram more stations in the band. ---
**Author:** ![McDeath\_the\_Mad](https://avatars.discourse-cdn.com/v4/letter/m/a3d4f5/32.png) [@McDeath\_the\_Mad](https://boards.straightdope.com/u/McDeath_the_Mad)\ **Post date:** [August 17, 2005, 5:44pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/14 "2005-08-17T17:44:23Z")
It’s not the stereo thing either, you can get AM Stereo radio stations as well. I’ve gotten them twice, both times in Alberta. It was an AM station and my Stereo light was lit up. The station was in stereo, but had no where near the quality of an FM stereo station. MtM ---
**Author:** ![whitetho](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whitetho/32/1059_2.png) [@whitetho](https://boards.straightdope.com/u/whitetho)\ **Post date:** [August 17, 2005, 11:11pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/15 "2005-08-17T23:11:13Z")
> [@scm1001](#): > > tx for the replies. Was the 5 kHz bandwidth chosen to cram more stations in the AM band? Or perhaps early recievers/speakers couldn’t handle any more? The “5 kHz limit” is nothing more than a widely believed myth. In the US, AM (mediumwave) stations are actually limited to 10 kHz audio. This causes some bandwith overlap between stations on adjacent frequencies, which is handled by avoiding putting stations on adjacent frequencies too close together. Although AM cannot match FM in fidelity, it is capable of far better sound quality that you have probably ever heard. In particular, many AM receivers are designed with the idea that all you will ever listen to is talk radio, so they cut off the response at 5 kHz – or even lower. Someone who grew up listening to a high quality receiver in the 1940s would be appalled at how bad present day AM receivers sound. For a more detailed review, I suggest looking at [The AM STEREO Page](http://users.hfx.eastlink.ca/~amstereo/amstereo.htm). ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [August 17, 2005, 11:19pm UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/16 "2005-08-17T23:19:11Z")
> [@Kevbo](#): > > FM baseband is limited to 12 Khz, so you still lose most of the top octave of human hearing range…but a lot of what is up there is not very “musical”. A violin, for example might sound better, as a lot of the scraping noise of the bow on the strings will be lost. EEeeekk! Quite the opposite. Much of the crucial timbral nuances will be lost with a 12KHz cutoff - which actually eliminates anything above the fifth overtone of the top notes of the violin. The sounds of some other instruments, especially percussion, will be affected even more. Classical music will not be a success with current commerical downloads, because the compression is shockingly bad when head through a half-decent system. ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [August 18, 2005, 2:39am UTC](https://boards.straightdope.com/t/why-does-am-radio-music-sound-different-than-fm/317246/17 "2005-08-18T02:39:36Z")
Part 73 FCC rules: > [@](#): > > (b) Emissions 10.2 kHz to 20 kHz removed from the carrier must > be attenuated at least 25 dB below the unmodulated carrier level, > emissions 20 kHz to 30 kHz removed from the carrier must be attenuated > at least 35 dB below the unmodulated carrier level, emissions 30 kHz to > 60 kHz removed from the carrier must be attenuated at least > [5 + 1 dB/kHz] below the unmodulated carrier level, and emissions between > 60 kHz and 75 kHz of the carrier frequency must be attenuated at least > 65 dB below the unmodulated carrier level. Emissions removed by more > than 75 kHz must be attenuated at least 43 + 10 Log (Power in watts) or > 80 dB below the unmodulated carrier level, whichever is the lesser > attenuation, except for transmitters having power less than 158 watts, > where the attenuation must be at least 65 dB below carrier level. That means that audio frequencies above approx. 10 kHz must have their total power limited to a small fraction of the total power output. AM radio can sound surprisingly good if the station’s engineers and management want to broadcast a clean signal. Unfortunately, most AM stations, like their FM counterparts, would rather sound loud than clean.