Hi,

If you wanted to make the best possible digital recordings from radio broadcasts, would you choose an FM feed or an MP2 feed? At what MP2 bitrate would your answer change?

Or is it not sensible to generalise, and I should consider each radio station on a case by case basis?

I currently record a lot of DVB satellite radio broadcasts (mainly the BBC's channels at 192kbps or 160kbps). I use a DVB-S receiver card to capture the MP2 stream directly to my computer - which is relatively cheap and easy and gives me a perfect "clone" of the broadcast.

In David Robinson's paper at http://www.david.robinson.org/commsbill/ he makes the following set of comparisons between FM and MP2:

* 256 kbps = much better than FM
* 192 kbps = almost always better than FM
* 160 kbps = about the same as FM, but sometimes better, sometimes worse
* 128 kbps = usually worse than FM, sometime much worse

I am interested to know opinions on how controversial these statements are. The paper itself does not go into much detail on the methodology used to come to these judgements.

Does "FM" refer to "average FM" or does it refer to FM at it's best (i.e. good aerial, strong signal, good quality tuner) ?

(I'm aware that David Robinson is active in these forums, which is why I've posted here.)

Apologies if this has been discussed before - I've browsed the forums, but the search facility doesn't let me search for "FM" because it contains less than 3 letters.

Thanks,

Dave.

If you search alt.radio.digital or uk.tech.digital-tv using google groups you'll find hundreds of pages of relevant debate!

You can search for two letter words on here by adding a *

FWIW I would do exactly what you are doing - grab the 192kbps mp2 feed from DSat or DTT and store it. Obviously DAB at 128kbps sounds worse.

FM broadcasts sound totally different because dynamic range compression is used much more. BBC Radio 2-4 on DAB/DTT/DSat have little if any DRC, whereas on FM Radios 2 and 4 are audibly processed all the time, and Radio 3 is "gently" processed some of the time. Radio 1 is trashed with multi-band DRC on all platforms, though to different amounts. Apart from this, a good recording from a good FM signal can sound excellent.

IME it's quite difficult to get a good FM signal with a PC switched on.


The figures in that report assumed good FM reception, with the "sometimes worse, sometimes better" statements indicating that, depending on the content, a psychoacoustic codec may struggle, or may have no audible flaws and also beat the FM noise floor by 20dB.

The comparison between mp2 performance and FM performance was extrapolated from the official MPEG listening test results, and the repeated observation that FM can be near-transparent under good conditions. Younger listeners hear the low pass, but don't judge it to be annoying. Few signals are audibly damaged by -70dB noise. Better encoders may improve the performance of any mp2 based system at a given bitrate, and obviously poor reception will blight FM.

I think the BBC stations on DAB sometimes sound surprisingly good for 128kbps mp2. However, the low bitrate is still usually the limiting factor on the audio quality.

I think many of the commercial stations on DAB sound truly awful at 128kbps mp2 - infact it takes great effort to make things sound so bad! I suspect lots of transcoding, poor encoders at sub-optimal settings, far too much dynamic range compression, and general incompetence or lack-of-interest from the broadcasters.


The simple answer to your question is listen to all options and pick one. All things being equal, I think 160-192kbps is the point where mp2 coding starts to match or beat good FM, but others swear that Radio 3 FM sounds nicer than 192kbps mp2. Sometimes I agree, but I still tend to listen to the BBC nationals on DTT (192kbps mp2 discrete stereo). What's more, I'm sure they'll be a 192kbps station somewhere that's transcoded from a 128kbps land-line link! In this case, the (hypothetical) analogue fed FM transmitter will sound much better.

Cheers,
David.

They're very controversial, because people have spent so much money on DAB that it must sound better. (or it all sounds the same anyway).

That's the usual argument in defence of 128kbps mp2 as a broadcast standard. As you might guess, I think it's rubbish!

Thanks for your quick response.

Most views I have read in the FM vs MP2 debates concentrate on criticising low bitrate MP2 - e.g. arguing that current UK DAB sounds worse than FM.

I would like to think that MP2 was a good choice for broadcast radio, and that given sufficient bitrate will generally beat FM in a listening test. Is that the case?

So I am more interested in how controversial the statements about 256kbps and 192kbps are, rather than the comments about 128kbps.

Most defenders of FM generally seem to be people who prefer the sound of analogue audio in general. As I am only planning on recording digitally, this probably isn't relevant.

Regards,

Dave.

I agree with David/2BDecided that it's definitely not as simple as it first might seem. IMO the following are all very important:

* whether best practice is being used at the broadcaster's offices

The broadcasters can, and frequently do, screw up the audio before it's even left their offices.


* the quality of the FM tuner

The difference between good and bad is huge, but you don't have to spend the earth to get a good one. This one is the best entry-level FM tuner:

Denon TU260L Mk2

The FM audio samples on my audio samples page were all recorded from that tuner (well, the Mk1, but I don't think there's much difference other than the Mk2 has RDS)


* the quality of the FM reception

Most people use the wire aerial that came with their hi-fi system of FM tuner, but the main problem with this is that you've got to have the aerial next to the hi-fi, which is usually in a high multipath environment, and this degrades your FM reception. I can't have an external aerial, so I use a £15 single-element FM dipole from Maplins:

aerial

and place it on my windowsill, and I get very good FM reception.


* which stations you want to listen to

Some stations (mainly pop stations) use very high levels of audio processing (dynamic range compression) on FM, which makes it tiring to listen to for prolonged periods of time and just generally completely alters the sound of the original track. The same stations on DAB and DTT/DSat still use high levels of audio processing, but just not quite as high as on FM.


I've recorded samples of Radio 3 off FM and off DAB for you to compare:

Radio 3 FM MP4 file 7 MB
Radio 3 DAB MP2 file 4.5 MB

There's a Winamp MP4 plug-in if you need one here:

MP4 plug-in 217 KB

The brief bits that sound like there's some "bubbling" on DAB is caused by the signal dropping briefly. It's a common problem on DAB.

Overall, I'd say that FM is capable of providing higher audio quality than 192kbps MP2, and IMO does so on Radio 3 and on some other well-engineered stations (another example for me is Smooth FM in Manchester), but frequently the audio is butchered to such an extent that you're better off with the DSat 192kbps MP2 streams. I'd definitely give DAB a miss because literally 98% of stereo stations in the UK use 128kbps MP2, and they sound awful, whereas most stations on DSat use higher bit rates than 128kbps for stereo. See:

Table of bit rates on different platforms

It depends on the station you're listening to. Taking Radios 1-4 on DSat at 192kbps and on FM, my opinion of them are as follows:

Radio 1 192kbps > FM because the audio processing is too high on FM
Radio 2 FM > 192kbps because Radio 2 192kbps (I've got DTT BTW) sounds flat
Radio 3 FM > 192kbps because FM sounds more natural IMO
Radio 4 192kbps > FM because even with low levels of hiss you can still hear it on FM but there isn't any on digital radio

So, as you can see, it's station-dependent.

Does anyone know for sure if the 192kbps BBC MP2 streams on DTT (DVB-T) and DSAT (DVB-S) are the same?

Has anyone attempted a bit-for-bit comparison, or even a visual comparison of the decoded WAV files? I've always assumed that it made no difference which 192kbps stream I recorded.

Thanks,

Dave.

We were told by someone on the uk.tech.digital-tv newsgroup who works at the BBC that they were identical because they used the same encoders, but now we know they're not the same because the DSat streams of Radios 1-4 use joint stereo whereas the streams on DTT use discrete stereo. They changed it just before Christmas. I'm not sure what the point of changing was because using discrete stereo disallows the encoder to use joint stereo altogether, so IMO bits will be wasted if the L and R channels are sufficiently similar not to warrant discrete stereo. But it's the BBC, so you become accustomed to seeing them do strange things.

At 192kbps and above, you're left with the chance of slight artefacts on some material (how big that chance is depends on the encoders and the source material), and the certainty of more processing on FM.

I think Radio 3 can sound nicer on FM (I don't think the others do), but I'm almost convinced it's the dynamic processing that brings up quiet parts (especially reverb tails) making the recording sound more "live" and "ambient".

IME a little extra background noise can sound nice too - it's a perpetual thing - your ears hear the noise, and consciously you wish it wasn't there - but subconsciously you "hear" anything you want to in the noise. What happens is that your auditory streaming processing finds anything which is believe is missing from the recording within the noise (whether it's there or not) and you believe the recording sounds more life-like. Your brains thinks a trumpet should have these harmonics - there are these frequencies (and all others!) in the noise, so the signal matches your brain's idea of a trumpet, and it sounds real to you. Without the noise, your brain can detect that the harmonics are absent, and it sounds less real to you. Only a theory, but you can test it yourself by adding a little noise to dead sounding CDs.

Importantly, you've got to remember that the FM transmitters are fed from NICAM (i.e. compressed 32kHz 14-bit digital) links, so they're not pure analogue in any sense! People who love FM because it's analogue and hate <whatever> because it's digital are quite simply talking out of their backsides!

If you're going to psychoacoustically encode the signal yourself, remember that you will be effectively transcoding, because the FM signal has already been through lossy NICAM compression. However, the wideband nature of NICAM compression doesn't seem to interact with psychoacoustic based codecs at all. It seems to behave like near-lossless codecs, which transcode very well (there have been threads about this on HA).

As digitalradiotech has said, grab both version for the station of interest, and listen for yourself!

Cheers,
David.

Is this a universal thing in the UK? What about local stations (both BBC and commercial), and other European broadcasters?

I'm aware that the French national stations use a satellite MP2 feed which is then retransmitted "as is" by the DAB transmitters, and also used to feed the analogue FM transmitters. Someone has mentioned that Germany does a similar thing.



Something I always wished I could do was to capture the NICAM data digitally - but I never found a card capable of doing it. The obvious question is if the BBC's digital TV 256kbps MP2 streams are superior to NICAM?



I don't want to invest in digital recording equipment for FM just to test it.

But I don't record Radio 3, so after reading the comments here, I'm happy to carry on as I am, knowing at least that my recordings are in the same ball-park as FM.

The next question is how best to listen to these MP2 recordings - but that's a different thread.

Thanks,

Dave.

If you have the equipment to store direct mp2 bitstream from DSat, but don't have a good FM tuner, roof-top aerial, good sound-card or CD recorder, then there's absolutely no question - and no point worrying about FM.

The NICAM digital links are for national BBC FM. I don't know about the locals. Commercial local stations (ILRs) seem to use MPEG compression of some sort to send their pseudo national output around the country - and all stations use MPEG links for some content.

NICAM 728 vs mp2 256kbps discrete stereo? That's not an easy question to answer. Mainly because there isn't a software Nicam encoder available to play with. NICAM has problem signals too - Harpsichord apparently (ironic - that's an MPEG problem signal as well!) and there are probably others.

I've heard many people say they prefer NICAM, but technically mp2 256kbps should beat it. Off Air reception of either has never troubled me, whereas off air DAB is painful! 192kbps mp2 doesn't always sound quite right off-air, but I can't reproduce the problems with my own encoding. It's difficult to be sure of off-air comparisons when there's no reference - it could be a fault in the source material.

Cheers,
David.

Try and get the best quality D to A conversion you can. I use S/PDIF digital output from my sound card to my Sony Minidisc player's digital input and use the MD player's DACs. This avoids the PC noise on the analogue signal and the MD player's DACs are pretty good (not brilliant, but not bad). I've done a page about this (it's a bit dumbed down for general consumption):

audio advice page

AV amps usually have a load of digital inputs these days and they're good value for money from various online retailers. If you want the best D to A conversion quality you can get then get a hi-fi separate DAC, but be prepared to pay a lot of dosh for it unless you buy one off eBay.