Internet Radio vs Broadcast FM Sound Quality

[classicalfan]

I listen frequently to KUSC, which is a classical music station from the University of Southern California. I can get it either directly from their FM broadcast or with their Internet feed.

Listening recently with headphones, and not really very expensive ones at that, I believe the overall sound quality is significantly better with the FM broadcast than over the Internet.

I'm wondering if that makes sense from a technical perspective, or if perhaps I'm just imagining a difference.

 

[MarcelvdG]

If they use the same Internet feed to get their signal from the studio to the transmitter site, then it doesn't make sense. If they use some lossy subband coder with a fairly low bitrate for the Internet feed and something better for the studio to transmitter link, then it may make sense. Streaming and FM broadcasting each have their own artifacts, so it just depends on what imperfections bother you least.

 

[evsentry3]

Internet feeds are bit rate reduced feeds. How much reduced depends on the costs willing to be paid.

Not typical at all to use this feed to get to a transmitter. Never have heard of that actually. Usually used is a linear link to a transmitter.

EV3

 

[classicalfan]

I'm pretty sure KUSC is wired analog to the transmitting tower. That connection was in place way before the Internet and I don't see any reason they would have changed it.

I found an article on this very subject regarding KUSC. It's an old post from 2007, so I don't know if the details are still accurate or not

"So briefly in summary, there is NO streaming quality that even approaches that of an FM signal. NONE. Secondly, there are very, very, very few stations that even stream at 128 kpbs, which I consider to be an "acceptable" quality, but certainly not one to brag about.

And finally, something that you are also unaware of is the matter of sampling rate, which is critical in the conversion of an analog signal to a digital computer file. The industry standard for this sampling rate is 44.1 khz, and almost every online radio station that is streaming classical music uses this sampling rate. A notable exception is station KUSC in Los Angeles, which streams with a sampling rate of 32 khz (and a bit rate of 96 kbps). They are being extra cheap with this sub-par sampling rate and it seriously affects the quality of their musical stream. This is inexcusable."

Here is a link to the complete post if anyone is interested:

COMPARE FM RADIO BROADCAST TO ONLINE STREAM - WavePad - NCH Software User Community Public Forums

And this would certainly explain what I have been experiencing.

 

[MarcelvdG]

I'm more familiar with the Dutch situation and most Dutch local radio stations switched to digital studio to transmitter links, often via Internet streams, when the company that controls the telephone lines stopped renting out bare copper lines. It's usually a different stream than the one that the listeners can listen to. Good to hear that normal analog lines are still available in the US.

Regarding 32 kHz sample rate, with good anti-alias filtering, that should just be enough for a 15 kHz audio bandwidth, like you have with FM broadcasting. That 96 kbit/s bit rate is quite low, though.

 

[Galu]

For anyone interested in the history of FM broadcasting in the UK, here is a comprehensive article from Jim Lesurf:

The BBC PCM / NICAM Story

Most people still think of FM radio as 'analogue'!

 

[classicalfan]

What's also interesting is that while I can hear a big difference with cheap headphones between the FM broadcast and Internet streaming, I can't really detect much difference with my speakers. Which I think proves what I already knew that I need new and better speakers.

 

[MarcelvdG]

Great article!

Digital signal interpolation on a Z80... I once built a circuit that used a Z80 to just store audio samples in a memory and that already required most of the processing power of an 8 MHz Z80H, programmed in machine code.