You've not read my previous posts?
It has an excellent downgrade potential which the broadcasters grabbed to save money. In the same way as with digital TV.
You've not read my previous posts?
If a portable radio is how you judge sound quality, it says rather a lot.
Your not that bloke;
"DAB sounds worse than FM" are you;?...
No. But DAB does sound s**te. Problem being having some expensive audio gear at home gets you used to stuff sounding good. The last car's original owner had fitted a £1200 audio upgrade which sounded fabulous on my high rate MP3s and CDs but the DAB was dire. FM sounded fine.
What you fail to understand, and it is quite complex, is that the AM modulated part is transmitted over the air as FM.
Take the L and R signals filter to 15kHz and add them to give L+R and subtract them to give L-R.
Generate a 19kHz tone. Double it to 38KHz. Use the 38kHz signal as the "carrier" in a double sideband suppressed carrier AM signal. (DSBSC)
Add L+R + 19kHz + DBSSC to give the baseband signal and apply that to wideband FM modulator. The whole lot is transmitted as FM.
In reception you receive the signal and demodulate the FM to get back the baseband.
You use (normally) a PLL to lock to the 19kHz tone and double it to get a phase locked 38kHZ signal which is used to reinsert the suppressed
38kHZ carrier. You can then demodulate the difference and get L-R. Low pass filtering gives you the L+R signal.Add L+R + L-R to 2L Subtract L+R - L-R to get -2R and invert to get 2R.
Job done.
The stereo FM signal is massively wider in bandwidth than the equivalent mono meaning the signal to noise ratio is much worse. So IIRC you need about 23dB better signal strength for the same signal to noise ratio for stereo over mono. Due to the way FM works, a weak signal will be inherently nosier at higher frequencies which appears as hiss. FM audio is already pre-emphasised to minimise this, the gain rises with increasing frequency into the FM modulator.
The interesting issue is human brains can accept and mask out a lot of the imperfections with analogue signals, we just learn to ignore the pops and hiss and hear the music still. Digital signals will sound "perfect" at signal levels that would be noisy for analogue. Then they drop off a cliff and you get burbles and break up and cant hear anything.
The issue with DAB is it is an old crappy codec that doesn't compress the audio as well as modern codecs do. In order to maximise profit, signals are encoded at very low bit rates and strangled bandwidth to squeeze more in. So you get the worst of both worlds perfectly reproduced crap audio and no way to in-situ upgrade to better codecs.
It is completely bogus. But hey never mind the quality... look at the choice of stations. Just that they all sound s**te.
Someone calculated that intelligible speech could, if tokenized, be sent down a 50bps channel. I.e imagine reduing it to text or sylalables sending that, and re synthesing a voice at the other end.
Even FM shit is now s**te as the Beeb doesnt bother sampling its own feeds internally at high rates.
Ages ago I put up some files of the same programme from DAB, FM and Freeview.
Asked those who say DAB is shit to say which was which. Got the same results as using a pin. ;-)
That is how some broadcasters choose to do it to save money. Same happens on FreeView TV.
Not an inherent fault with DAB.
You might as well say a CD played on the average radio FM station sounds nothing like it does at home. Due to the signal processing all broadcasters use. That is nothing to do with the FM medium.
The difference in sound between CD and vinyl has nothing to do with the media too. Its down to the different processing needed to get a reasonable sound out of vinyl that they don't have to do on CDs. CDs being closer to the original but some still prefer the distortion in vinyl.
It's not distortion - it's "musicality"
FFS people, I made a comment that the stereo difference signal is more fragile than the main sum of the channels signal. This appears to be something that everyone agrees with, so why keep romping off down rabbit holes about how you name that bit of the signal?
Yup nice description... Pretty similar to how they described it in our transmissions system lectures some 30 odd years ago.
For certain values of "perfect" - if you make the "wrong" trade-offs in filtering, dithering, sample rate / depth, codec, reconstitution etc its not difficult to end up with something perfect that is not at all pleasant to listen to.
Indeed, case in point. In some respects the system development was a little ahead of its time - results would probably been better with another few years of development and experience in digital audio coding, before nailing it down as a standard. (and a more flexible spec would probably have helped greatly).
Still if you think DAB sounds bad, try listening to LPC-10 audio encoded at 600 bps. (actually quite intelligible for speech so long as one speaks slowly with distinct gaps between the words)
With the possible caveat that in moving receiver applications, and high ambient noise environments, you *might* value the lack of fading etc as a benefit that outweighs the loss of absolute quality. Cople that with the fact that many people seem to be blissfully unaware of the lack of fidelity in their audio, and enough people put up with it without that much complaint.
(personally if the radio quality is crap I would rather listen to a CD etc anyway).
I have done it on military systems at 600 bps[1] using a LPC-10 vocoder. Its far from telephony channel quality, and loses pretty much all character to the voice, but it is surprisingly intelligible so long as the speaker is trained to speak with discrete pauses between words.
[1] which could then be sent with FEC and crypto layered on top over even poor quality HF channels using a radio modem. With frequency agile transceivers, it made a robust comms channel that was pretty much undetectable let alone recoverable to the wrong people, and nicely skirted round most ECM systems as well.
Ever heard stations running the AAC+ or DAB2 codec at decent i.e.
112/128 K bit rates?..
Err, it has.
Different processing will of course make then sound different. But vinyl has inherent distortion - second harmonic?
Quite. Can make certain instruments sound more 'exciting'.
Yes they IIRC call it a Vocoder used in mobile telephony and similar low rate applications..
Can you be a bit more specific in that statement?..
I do tend to laugh at those saying DAB is crap because it may not be transmitted in what they consider true stereo. Then go on about listing on a portable radio or car FM. When in a car, the decoder spends much of its time blending stereo to mono. Except in high signal strength areas.
The fault with DAB is you cannot upgrade the codec to anything acceptable by 2019 standards. So we're stuck with a poorly performing codec and then have bean counters forcing low bitrate streams. Bad codec and then constraining the bit rate is a recipe for shitness.
I'm sure you can find something at a semi-acceptable bit rate on DAB. But the stuff I listen to such as DAB R4 is in mono. On R4 FM I can listen to The Archers in stereo. I can hear people enter on the left, walk into the centre and exit stage right. It's really quite good. And on DAB that is all missing. Not a big issue when driving but I have a stereo system in the kitchen area. We spend a lot of time in there cooking and eating and we can listen to CDs in stereo, The Archers in stereo for example. And DAB is not an improvement but a significant downgrade in comparison.
That's not a fault of DAB, per se, but of how it is used. In my bedroom I get a rock steady DAB signal, while FM wanders in and out.
Then don't use DAB. If you have a decent stereo system, it surely isn't your only choice?
Correct. Especially given an FM car radio will spend much of its time in mono anyway.
DAB was specifically designed for reception on the move.
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