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-   -   Audio quality vs dropouts (http://www.drmrx.org/forum/showthread.php?t=1416)

Digi 27-05-2006 14:16

Audio quality vs dropouts
Its interesting for me really what's the opinion of the forum participants - which of the rates - 14 kbps with less audio quality and no SBR but without drops, compared to the higher bit-rates with SBR but with some short droputs, is making more sense in terms of listenability?

Of course assuming we can't have both :)


Alan Johnson 27-05-2006 15:38

I find drop-outs more annoying than lower audio quality - of course, as a long-term shortwave listener, I'm used to poor audio quality!

FritzWue 27-05-2006 16:02

One of the purposes of DRM is to bring back the listeners to long-/ medium-/ shortwave that left for better audio quality on FM, DVB, DAB, Internet etc..
These listeners will only come back if DRM provides "near FM" audio quality.
We already have lower quality in AM, so additional DRM in low quality makes no sense, also see my sig.

mitajohn 27-05-2006 18:29


One of the purposes of DRM....

I agree with this but also even <99% CDA is very annoying to the listener but perhaps not to the DXer. "They" must find a compromise between these two states. Which are the other purposes ?


df9rb 28-05-2006 07:23

About 1 year ago I proposed to transmit the audio data stream as a combination of a low audio quality main stream containing all data for a basic audio playback and additional data for higher quality as an add on.
The idea was to transmit in 64-QAM where the low audio quality stream is using only the 16-QAM subset - the high quality add on stream uses the remaining carriers (bits). The listener (and/or the software) decides between robustness or quality.
There was now reaction last year. I don t know if my idea can not be realized for technical reasons ( I am not a specialist in DRM) or nobody wants to expand the specification.

Bernd, DF9RB

mitajohn 28-05-2006 07:47

Yes, this seems promising. But another matter which, in my opinion, is very important, is the sensitivity of DRM to interference wherever it comes from. A year passed now experimenting with DRM and the most serious problem I have faced is the interfering carriers to the DRM signal. It seems to me that the system suffers from this kind of disturbance, there must be a way to minimize this, but I don't know how it would be implemented.


FritzWue 28-05-2006 08:19

mitajohn: "<99% CDA is very annoying to the listener"

I also think 99% CDA is really the lowest limit for non DXers.
This may be a single 36 seconds dropout per hour, listeners will change channel then.

mitajohn: "the sensitivity of DRM to interference"

Why not propose splitting the sw radio bands in DRM and non-DRM parts?
But even then we need very selective receivers. My DRT1 with 12kHz crystal filter often has problems with DRM on 6085kHz and 6095kHz. If one of them is more than 20dB stronger than the other the weaker has dropouts.

Is it really possible to do what Bernd DF9RB is proposing?
...would be a real improvement to have reduced quality instead of dropouts.

simone 28-05-2006 20:15

Hierarchical modulation is possible on the digital transmissions and is in the specification, but I think the same people if not more would be complaining about low audio quality. On the other hand many people complaining about too many dropouts are not in the service area of the transmission they are receiving. Also many transmissions do not use the best configurations for the channels they are using, especially with changing conditions. Actually the settings determine the service area to a great extend.
A more interesting approach was done a few years ago using a receiver (or better even more than one) in the target area and use the feedback to alter the settings at the Tx, so according to the actual conditions the best quality for a given service area can be used at any time.
Btw the information given in the AFs often seem quite optimistic concerning the coverage area ;)

radiomann 28-05-2006 20:36

i stated this ages ago, the average person will not listen to any station with dropouts, that has always been my main concern, sur dxers will accept 98.5% but people who listen to radio day in day out won't and i don't blame them, ans DRM via Sw will ALWAYS be like that.


sveron 28-05-2006 22:46

Hello to all,

I agree with what was said before. I prefer lower audio quality than short drop-outs, even if a goal of DRM is to give near FM quality to the AM bands.

I will now develop because I have time, my DigitalWorldTraveller crashed on saturday. And french people like to talk :-) A few ideas :

1 - Of my family experience of DRM

I listen daily to RTL, Radio Luxembourg, DW or BBC using my hi-fi system and wireless headphones, so I can work in the garden, the kitchen or anywhere else, keeping in touch with DRM. I let the headphones on a place with the sound very loud (but the quality is still there) so members of my family can listen to these stations too. They were really more annoyed by the drop-outs than by the fact that audio could not be 'FM-like'.

Of course, we are a kind of french family used to listen to RTL or Europe 1 on longwave because of the poor FM coverage, so even the DW with the 'very ugly' 14kbps without SBR is good for me, compared to the recent audio treatment added on Junglinster 234LW and Felsberg 183LW. Drop-outs are just okay for me because I listen to shortwave for 10 years now, not for the people around me. I cannot say if someone used to listen to FM networks only will accept such low bitrate.

2 - Of the audio level on digital feeds

Honestly, I will even say that 14kbps without SBR from Deutsche Welle is more comfortable for me to listen, compared to the 20kbps p-stereo by RTL 5990, which keeps having huge audio level differences between music/jingles/talk/advertisment sources (see my past posts in this topic). It is so annoying that I always have to play with the sound level settings when listening to RTL. In my opinion, audio treatment on their digital feed is really a problem here, and I am still amazed that they keep continuing their tests, feeding their DRM transmitter with this bad audio source. Or maybe they really want the advertisment on air to be really loud, such a shame ! (Junglinster then not being under the french regulation body's control)

3 - Of the audio processing before DRM encoding

Another matter for the broadcasters is to avoid the multiple use of codecs before the DRM encoding. The less "worked" the audio is before encoding, the better it will sound at a lower bitrate. I consider the work made by CVC is the best, their recent tests from Jülich had a very pleasant audio, I would be curious to listen to them with lower bitrate and no SBR.

I also noticed that RFI 3965 audio with 14kbps was better when someone was talking from a phone than from the studio itself, so... audio processing differences ?

4 - Of the numerous problems experienced during 11 months of almost daily DRM listening

And yes, there are also problems, for example when DW is at 32dB SNR on 5980 at night and RTL 'only' 25dB on 5990 with a little fading, RTL won't work properly...

I am very worried with local interferences, if somebody switches the light in the house, even 2 stairs lower, it will cause problems in some cases. And ceramic heaters are hell. I only chose to let my appartment 'freezing' for some DXing when I was studying, but I guess that won't be the choice of the 'average listener'. And that wasn't my choice last winter :-) Robustness mode on DRM would be absolutely necessary with light switchings, helpless with ceramic heaters.

I also had serious problems with traditional power line (Parisian countryside, nature all around except this line) and hotel surrounding (Charlottenburger Bahnhof in Berlin or small village on Rügen island).

5 - Of DRM and the future of intl public broadcasters with a tight budget

Now, just a small suggestion... I would be curious to listen to tests made on long distances with HVXC or CELP encoding at moderate bitrates (7-14kbps with or without SBR) and big robustness mode. It might be a solution for international broadcasters focused on talk programmes : I think the people buying a DigitalRadio receiver, and finding 'Voice Of Russia' or 'Radio Vatican' in the receiver's scan list, and making the effort to listen to them, will be the same kind of the ones who listened to AM shortwave. It will stay an effort to listen to a foreign current affairs or cultural programme. There won't be a 'digital miracle' for international broadcasters. Will these curious listeners care about the audio quality, even lower than FM, if they are sure to find the station everyday to get some news with other points of view, and don't have to care, if they are even aware, about seasonal frequency changes ? DRM leaves the listener free of the tuning problem, which is important when people 'have no time' these days. People also left shortwave because they don't have time to search for the station, so what if the receiver makes it on its own, and the audio quality is still low ? That is an interesting question...

One of the goals of DRM is to reduce the power bill at the transmitter, because there's a big move to reduce or delete foreign services by public broadcasters (cf. Radio Slovakia's decision this week). So I don't personnally care if the audio quality of international broadcasters on DRM is the same than a 10kbps RealAudio stream online. Because it will just be radio that I can listen freely, and it will keep existing in a world where money is the big matter even for public services. It is sad to say that, and of course I will always prefer high quality AM or DRM, but I think we might give up for audio quality at the expense of new receivers if we want to keep public international broadcasters alive. At least they will save money from transmitter costs once DRM is introduced in areas where people can afford buying DigitalRadio sets.


This is all I wanted to say for now... Beyond the bitrate problem, the matter is to know how deep the stations using DRM will be involved in keeping a pleasant audio treatment, a stable audio level (and useful associated text/data/epg). These parts of the processing chain will be part of the DRM success.

All that reflects only my opinion of young shortwave listener, thank you for having read this long thing.

73, de Stephane

DRM-OM 01-06-2006 22:03


Originally Posted by radiomann
but people who listen to radio day in day out won't (...) DRM via Sw will ALWAYS be like that.

see also my long term observations.
Nearly every of the transmissions were total or main failure at least once in two weeks, whereas perfect the rest of the time.


Originally Posted by simone
On the other hand many people complaining about too many dropouts are not in the service area of the transmission they are receiving.

Hi Simone,

I hear this thing over and over again, and if this is really the official comment about this I can only draw the conclusion that DRM reduces the coverage area.
Note that I refer to the fact that I compare transmissions that I listened in AM for 20 years and cannot get useful reception in DRM now.

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