Do they think we do not hear the difference?

[NHTL]

I find it increasingly disappointing that the BBC appear to think that we will not notice that Radio 3 is being broadcast in low quality on DAB. It is now gone 8pm on Sunday 24 February 2013 and Radio 3 is still broadcasting at 160 kbps Joint Stereo on Radio 3. We can hear the difference, are they trying to introduce lower quality by stealth? I find it so sad that they may think that we cannot hear the difference.

[Gordon]

A much discussed ssue NHTL! I do most of my listening on a small Sony "HiFi" [I hesitate to call it that but it has separate speakers and a CD player asi well] which is tolerably good. The DAB signal here is very good and there is no evidence whatever of any bioling mud! I honestly can say I can't hear any difference between the various settings used for R3 on that device. OK so I have cloth ears and I probably am not lstening carefully anyway, it's in the office. I listen to radio very rarely on the main HiFi elsewhere in the house so can't comment on any more concentrated listening on better equipment - and possibly a direct comparison with the FM simulcast.

I am curious; what is it that makes it possible to hear that difference? What should I listen out for as defects?

The JS coding will affect the stereo soundstage to some extent - you can't hear that very well on a portable or even one where the speakers in a separate system are oddly placed - and the bit savings can be used to better code the audio itself. However as R3 is supposed to be 192 "true" stereo the drop to 160 is significant [12:10 or 20%] and salvaged a bit by using JS.

In the case of many people listening on simple [mono] portables they won't hear much in the way of "quality" sound anyway so one could argue that the majority of listeners would not notice. I don't believe that the BBC is doing anything "by stealth" here, basically, as we have known for years, that multiplex is too full with programmes coming and going. One would have expected the R3 stream to be back up to 192 at that time of the evening.

[Bryn]

For me, the main difference is indeed the sound-stage. Instruments can seem to move about depending upon which register they playing in and what other sounds are accompanying them. I don't detect much change in the tonal quality as such. That is due to the very primitive form of intensity 'stereo' used for mp2's "joint stereo". There again, I listen to Radio 3 via DAB so much these days. It tends to be FM for live listening (due to not currently having any DAB tuner connected to my main serious listening systems) and HD Sound from the iPlayer for time shifted audition.

[Resurrection Man]

This is an interesting comment from another website regarding the loudness levels in DAB

http://www.listenersguide.org.uk/library/articles/?article=lg135

[David-G]

Could someone explain what "Joint Stereo" is and what uses it?

[jayne lee wilson]

Maybe it's my female ears, but even DAB at 192 is ruined by the string tone, especially on massed orchestral strings. Where it's not overtly edgy it's very hard and dull, essentially un-musical compared to FM, or R3HD at 320 kbps AAC. At one time I used the first Arcam Alpha 10, whilst a friend had the original Technics - both hi-spec, sophisticated devices which made the most of the less-compressed dynamic range but also showed up those source-deficiencies. Later this guy trialled an AVI DAB tuner, he reported it as " a bit smoother but tonally completely dead"! As for DAB at 160... strictly unlistenable.
Discussing it in the context of Brucknerian string counterpoint, I remember saying "it's at its worst where the edges rub"!

Portables are a different matter of course, but I usually still perceive that edginess even on them. But DAB (or any mp2 source) below 256 is just impossible for me in a hifi context.

The Berlin DCH ran at max. 320 AAC for about a year, it was a treat! Now the max is 256, and whilst, say, Lutoslawski or Dutilleux sound good and enjoyable, when the massed strings return for Brahms or Schumann I hear that hardness or dryness, a lack of "delicacy" is there again - not ruinously with AAC, but it does reduce my enjoyment.

[Gordon]

Could someone explain what "Joint Stereo" is and what uses it?

Joint stereo [JS] is where the true separate R and L signals are not coded independently although there is obviously a lot of similarity between them a lot of the time. That similarlty is exploited in JS so that the stereo effect only gets rendered vai the loudness of the R and L signals. Any time of arrival differences at each ear are largely lost and so there is a degradation in the perceived stereo image or soundstage. The bits that are saved in this process are used to give to the coding of tonal/spectral information and that "justifies" a drop in bit rate!

It's available for use in most audio compression systems. EDIT: In principle, the more granular the compression algorithm is and the more complex and analytical it is the better it will do the job in JS. The MP2 algorithm is not really sophisticated enough to do an excellent job in JS mode. The effects that Bryn highlights above will be less apparent if spectrum analysis is finer.

[Gordon]

Maybe it's my female ears, but even DAB at 192 is ruined by the string tone, especially on massed orchestral strings. Where it's not overtly edgy it's very hard and dull, essentially un-musical compared to FM, or R3HD at 320 kbps AAC. At one time I used the first Arcam Alpha 10, whilst a friend had the original Technics - both hi-spec, sophisticated devices which made the most of the less-compressed dynamic range but also showed up those source-deficiencies. Later this guy trialled an AVI DAB tuner, he reported it as " a bit smoother but tonally completely dead"! As for DAB at 160... strictly unlistenable.Discussing it in the context of Brucknerian string counterpoint, I remember saying "it's at its worst where the edges rub"!

Portables are a different matter of course, but I usually still perceive that edginess even on them. But DAB (or any mp2 source) below 256 is just impossible for me in a hifi context.

The Berlin DCH ran at max. 320 AAC for about a year, it was a treat! Now the max is 256, and whilst, say, Lutoslawski or Dutilleux sound good and enjoyable, when the massed strings return for Brahms or Schumann I hear that hardness or dryness, a lack of "delicacy" is there again - not ruinously with AAC, but it does reduce my enjoyment.

You must have exceptional ears then JLL. I have no perception whatever of the highlighted part of your post. Must be my age. Oh to be 17 again.

[Gordon]

This is an interesting comment from another website regarding the loudness levels in DAB

http://www.listenersguide.org.uk/lib...?article=lg135

That article says this:

"The continuity between programmes is set at a loudness level much higher than the programme content. Where that continuity contains trailers, this extra loudness is intrusive enough to make us reach for the volume only to have to turn it back up for the programme itself."

which has absolutely nothing to do with DAB as such, it happens in FM as well [pace the dreaded OptiMod] and is especially problematic in TV. It has a lot to do with studio practice rather than technology per se. The regulator has for many years had problems with loudness esp with adverts and the old IBA [died 1990] had untold trouble with the ITV companies boosting the DR of the audio during the breaks. There was even a special study group in the EBU concerned with the issue. The measurement of "loudness" [or "programme level"] was a great controversy back then and the different methods were used to justify the practice of manipulating the DR. The BBC pioneered the use of peak reading meters [because of FM level/deviation control being important] rather than the older VU [Volume Unit, prevalent in the USA] average reading ones and all sorts of "quasi peak" schemes were thought up. For R3 of course this is more important because of the wide DR of music. Listening in a car to R3 is virtually a waste of time. R1 however has such a small DR that it makes no difference. You can hear the DR control pumping in and out all the time. Ultimately it is the Mark I human ear that ends up having to make sense of it all.

As regards the DRC : this is a receiver only feature which most manufacturers do not implement, not even in cars where it might be useful. IOW the transmission is full uncompressed DR at all times. It plays with the scale factors in the reciver during de-compression of the audio to reduce the DR. My Sony radio allows you to select this parameter and alter it between 3 settings - none of them appear to do anything!!

[jayne lee wilson]

You must have exceptional ears then JLL. I have no perception whatever of the highlighted part of your post. Must be my age. Oh to be 17 again.

Well, I think I might be a bit happier at 17+40 than I was at 17...

Mum (91) has the Arcam 10 in her bedroom (hifi crammed in among the cosmetics, speakers looming over you at the dresser) and has no problem with it on Classic FM or Radio 3 - it is indeed all about the handling/hearing of high frequencies. (She was last measured as hearing nothing above 5khz).
Some more recent DAB models may of course have some technical sleight-of-hand going on to try to make it more listenable. I think Richard Black once suggested that cutting off at 14khz could solve the problem, but no-one would do it (or admit to doing it...) because it would be less extended than FM!

The Alpha 10 implemented the DRC and it certainly worked - not that I cared for it much - you should have heard it on level 5!

[ahinton]

I think Richard Black once suggested that cutting off at 14khz could solve the problem, but no-one would do it (or admit to doing it...) because it would be less extended than FM!

Ah, so you know ze excellent Herr Doktor Richard Schwarz!...

[Gordon]

.... I think Richard Black once suggested that cutting off at 14khz could solve the problem, but no-one would do it (or admit to doing it...) because it would be less extended than FM!

Well FM only just gets to 15kHz, the transmission spec asks for better than 3 down at this frequency so there's not much point in a receiver getting much further. IOW a receiver claiming audio out to say 18 kHz is a waste of time. Pilot tone rejection has to be -40 wrt the 15 kHz spot in a receiver too so I imagine that designers will dip the audio to get that spec in with a simpler, cheaper filter. 14 kHz in DAB at say 3 down wouldn't be that much different, other things being equal. Funny how a slight lift around 3-6kHz and a touch of 2nd harmonic warms sound up too.

There's a lot to building an audio filter [the phase/transient response] than meets the ear!! It has been suggested that some of the criticism of digital sound in general is due to the sharp filters used for anti-aliassing - flat as possible to close to 22 kHz and then as fast as possible therafter. Malcolm Hawksford at Essex has done a lot of work on this and demonstrated that part of the problem is the severe transient performance that can result. Slower filters would be better but then the HiFi fan would consider the apparent loss of bandwidth a "bad thing".

DAB tricks as such in receivers are not out of the question [any more than they are in analogue] there being no definitive specification to meet. Look at any HiFi FM tuner [real ones I mean] and see how sparse the quoted specs are and how veiled the methods of measurement are. The sound of any HiFi unit isn't just down to the technology it implements as any tweaker will undoubtedly tell you. Maybe DAB uses the wrong sort of wire?

[Resurrection Man]

....Maybe DAB uses the wrong sort of wire?

DAB = Debatable Audio Benefit ?

Desperately After Backing ?

[Gordon]

DAB = Debatable Audio Benefit ?

Desperately After Backing ?

Downright Awful Broadcasting?

[An_Inspector_Calls]

There's a lot to building an audio filter [the phase/transient response] than meets the ear!! It has been suggested that some of the criticism of digital sound in general is due to the sharp filters used for anti-aliassing - flat as possible to close to 22 kHz and then as fast as possible therafter. Malcolm Hawksford at Essex has done a lot of work on this and demonstrated that part of the problem is the severe transient performance that can result. Slower filters would be better but then the HiFi fan would consider the apparent loss of bandwidth a "bad thing".

If you compare the frequency and phase responses of a single element filters then it's easy to see that a ninety degree phase change occurs, pivoted about the frequency 3 dB point. (Isn't it clever the way the phono RIAA characteristic manages to achieve a constant 6 dB/octave roll off, and thus a constant phase change across the whole audio spectrum?) The frequency and phase change rates gets more severe if you increase the number of elements of the filter. Is it any wonder, then, that the 22 kHz cut-off of a CD is going to mess up the phase response of the recording, esp. at high frequencies? And perhaps that explains why the trasient response from LP is usually far better than that from CDS?

As for mp2 and distortion on string tone: I used to complain about that as well, but rather that than all the dross of FM. I'm using a Humax Freeview receiver piped into a Chord DSC1500E DAC driving ATC SCM100asl and otherwise mp2 sounds pretty good. But I happen to think that it's got better in recent years. Don't know why, but I don't notice so much distortion on string tone now compared to before.