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Good FM vs AAC streams

Nick_G

Nick_G

pfm Member
I just did a comparison of BBC Radio 2 on my newly acquired Yamaha T-2 FM tuner vs the 128k AAC stream of the same on the Squeezebox. The T-2 comprehensively thrashed the AAC stream, in a really obvious way! This was during a Nat King Cole track on Lisa Tarbuck's show. There was a much more palpable sense of space, depth and more precise stereo imaging. I have never heard the Squeezebox trounced so comprehensively. It just sounded so much more real, and life-like. The T-85, which used to be my benchmark had a different character to the AAC stream but it was only slightly better.

Previously, I would probably have said that the AAC streams were a good enough substitute, as in general it was debatable whether my other tuners produced better audio; they sounded a bit different. But the T-2 seems to be in a league of its own.

Perhaps if the bitrates were upped to 320k then it would be harder to choose. I will have to compare Radio 3 HD with the FM version next...

Regards,
Nick
 
The Radio 3 320k stream is excellent, certainly better than I remember FM - which was itself very good. Better frequency range, better dynamics, better detail, that sort of thing.
 
What I'd like to know is what is it about FM that makes it so good at conveying ambience, space & depth compared to even the high-quality AAC streams?

I also wonder if it has something to do with the way the signal is captured. The T-2 uses old-school analogue tuning i.e. a dial & pointer and it does sound different to the other tuners I have which employ digital synthesiser tuning. I've heard that this can be detrimental to the sound but I'm not sure why.
 
you cant generalize. it doesn't.

AAC stream at high rates has wider bandwidth than FM. at lower rates, lower bandwidth.

outside of that, theres no doubt a healthy dose of expectation bias at play.

(dedicated tuner vs "cheap plastic ", blah blah. completely wrong of course, but id bet my life on it existing)
 
Nick_G said:
What I'd like to know is what is it about FM that makes it so good at conveying ambience, space & depth compared to even the high-quality AAC streams?
Click to expand...

I'm sure things have changed, but back in the 70s when FM was recognised by many as the highest quality source available it was distributed digitally - using, I seem to remember, 13 bit samples.
 
I'm sure it has been discussed here before on PFM but the FM signal certainly isn't analogue all the way. I had a Naim NAT05 tuner and there was no difference between FM and streamed digital - is there such a thing as nostalgia bias?
 
Yes there was digital distribution in the 70's in the UK using IIRC a variant of NICAM (later used on analogue TV for digital sound). It may have been 13 bit, I don't have the white paper to hand but a noise masking algorithm would have been used to dynamically allocate those bits to where they're needed most to appear like a system with a larger bit depth.

Bandwidth isn't the only factor to enable lower bit rates with lossy compression either. Yes you can reduce bit rate by reducing the bandwidth encoded but equally you can keep the bandwidth and opt to throw more of the signal away in the hope that you won't notice it much. Remember that compressed (in the digital sense) audio relies on throwing away stuff your brain supposedly can't hear. It's why low bit rate audio sounds so odd because the artefacts of doing this can be quite objectionable.
 
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