Comment by rurp
7 years ago
I have a related question that someone here probably has a good answer for. I recently heard a song I like on the radio while driving. Shortly after it played I pulled up the same song on Spotify with my phone, plugged my phone into the car stereo through the headphone jack, and played it. The quality was MUCH worse. What's the likely reason for that?
I know very little about audio but my best guesses are:
1. The media cable was poor quality and/or playing music through the headphone jack is worse quality than radio station airwaves.
2. Spotify was sending back poor quality audio, possibly because I was not on wifi.
I'm sure the particulars matter but does anyone have a best guess as to why the quality would be so much worse? I don't really expect mainstream radio stations to serve up the highest quality audio, but maybe my assumptions are way off.
Radio stations often do additional processing of music to make it louder and more crisp when played on a car stereo, often by using techniques such as multi-band compression: the sounds is decomposed into several bands, and each band has dynamic range compression applied with different parameters to maximize the perceived sharpness/loudness.
It destroys a lot of subtlety and sonic detail in the original, but in exchange you get an overall louder, more in-your-face sound, with highs that come through even on bad audio systems. On car stereos, where you have a lot of low-frequency rumbling sounds, this especially makes a difference. And if you ask a random person to give a subjective quality assessment of original vs that processed audio, they'll almost always feel as if the latter is of higher quality.
For more info see e.g. [1].
[1]: https://www.soundonsound.com/techniques/multi-band-compressi..., section "Broadcast Applications for Multi-Band Compression."
Spotify definitely sends you low quality audio at times. Most people won't notice on common speakers and headphones, but even my "bad" speakers revealed the difference.
Amazon Music seems to be pretty good as far as quality is concerned. I think they download the MP3s onto the phone's local storage so they don't have bandwidth issues? Either way, I could hear the difference between Spotify and Amazon music. The difference between Amazon music and my own MP3s was not as apparent.
Pandora seems to sound "fine", although I seldom play it loud enough to notice. Spotify was the only one where I noticed the quality being notably bad. It's possible it's due to a low bandwidth fallback. And maybe they throttle their own servers at peak times, in addition to detecting the lack of local wi-fi.
The other thing to note is that Spotify will send you lower quality audio on the mobile vs. desktop client.
When I last moved, I plugged my phone (running Spotify) into my receiver to check that I'd gotten my speakers set up right. It was so muffled-sounding that I was worried I'd somehow damaged my speakers!
3. The A/D converter used by your car stereo headphone jack is low quality and introduced sampling artifacts.
4. You have a high definition radio and were listening to a high quality digital signal over FM as opposed to an FM analog signal.
It's probably a combination of all of these.
There is no "high definition radio." In the context of FM radio the H stands for hybrid and the D stands for digital. The digital often sounds worse when you compare them. Less noise for sure, but synthetic treble, almost as bad as Sirius XM.
Digital radio is very very low bitrate. A good FM signal is superior.
FM is capable of the same frequency response as CD, and it's a purely analog signal. If you don't have interference, you are getting a very pure stream of audio. The station is also probably using CD grade audio, so most of that quality is preserved.
From an audio standpoint, FM is a pretty decent sound medium. It's going to depend on your equipment, signal, and if you are moving.
There's quality setting in app settings, where you can choose the quality. Choices are automatic, low, normal, high very high. I guess "automatic" can adjust the quality based on connection.
I don't know if this is still common practice, but radio edits were often mastered differently back when I briefly studied music production. The station also likely uses signal processing to compress the dynamic range and increase the "loudness". Listening in a car is quite different than listening on home audio equipment, hence the different processing.
Spotify has compressed audio at pretty low bitrate. The FM signal has a full 20hz to 20khz frequency response and they are probably playing CD quality audio. Since it's just raw analog audio represented by radio frequency, it sounds better than the compressed stuff on spotify.
If you have a good signal, FM can be very high fidelity. Ever since people ditched CDs we've been listening to low quality streams and rips.