Digital radio DAB + - how does it work and is it really necessary?
Hi, Habr.
In recent years, the introduction of digital radio standard DAB + has been discussed in Russia, Ukraine and Belarus. And if in Russia the process has not yet advanced, in Ukraine and Belarus, it seems, they have already moved on to test broadcasting.
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How does it work, what are the pros and cons, and is it really necessary? Details under the cut.
The idea of ​​digital radio began to emerge in the late 80s, when it became clear that there was not enough room for everyone in the usual FM range - in large cities the free spectrum in the range of 88-108 MHz was exhausted. In this regard, DAB was considered a good alternative - it is a digital standard in which, due to more efficient coding, more stations can be placed. In the first version of DAB, the MP2 codec was used, in the second version (DAB +) the newer HE-AAC. By itself, the standard by modern standards is very old - the first station DAB earned in 1995, and the station DAB + in 2007m. Moreover, the “age” of the standard is in this case even more likely than a minus - now there is no problem to buy a radio for every taste and budget.
DAB differs from the usual FM quite a lot. And the point is not that one is a “figure”, but the other is an “analog”. The very principle of content transfer is different. In FM, each station broadcasts independently, and in DAB + all stations are combined into a “multiplex”, each of which can have up to 16 stations. There are different frequency channels, so different countries can choose those that are free from other services.
From a business point of view, this difference raises a number of disputes among broadcasters about how to broadcast in multiplex. Previously, the broadcasters themselves obtained a license for the frequency, bought an antenna and a transmitter, now the license will be issued to the multiplex operator, and he will already rent channels to radio stations. Better or worse, it is difficult to say, it is more convenient for someone to have everything of their own, someone is more comfortable for renting.
By the way, in this regard, DAB has a huge and fat minus for the listener - the price of renting a multiplex depends on the bitrate . And if you choose between 192 and 64kbps ... all I think is clear what will be chosen. If broadcasting with poor quality in FM is rather difficult, in DAB it is even economically encouraged (it is clear that this is not the fault of the developers of the standard, but nonetheless). Russian prices are, of course, unknown, while English prices can be found here for an example.
From a technical point of view, DAB + multiplex is a broadband signal, with a spectrum width of about 1.5 MHz, which is clearly visible with an RTL-SDR receiver.
A more detailed description in PDF can be found here .
There are not so many of them. DAB + is used in Europe, HD Radio is popular in the USA, DRM was used in experiments in India, but it's hard to say how they ended.
The map is a bit outdated (in Russia DRM was also tested, but it was abandoned this way), but the general idea can be understood:
A source
Unlike DAB, the creators of the standard HD Radio went the other way - the digital signal is placed directly next to the analog one, which allows broadcasters to use their own antennas and masts.
However, this does not solve the problem, because of which it all began - the problem of lack of empty seats in the spectrum. Yes, and purely geographically (and probably politically), in the ex-CIS countries, the adoption of a European standard looks more logical than using the American standard - the choice of European goods is still more and it is easier to buy receivers. In 2011, there were still references to the Russian RAVIS standard , but everything went out of the way (and thank goodness, since there is no compatible own digital standard with anything, this is the worst that could be thought of for radio listeners).
Finally, we turn to the practical part, i.e. for testing. In Russia, DAB does not work yet, so we will use SDR records from the Dutch multiplex. Those interested in other countries can also join and send me IQ records, I will process them and make a pivot table.
How can you listen to DAB? Because digital standard, you can decode it using a computer and rtl-sdr receiver. There are two programs - qt-dab and Welle.io , both can work with rtl-sdr.
Qt-dab looks like a student’s coursework, and the author obviously didn’t bother with the design - the fonts don’t fit into the controls, the windows do not scale. But for us the most important thing is that it allows you to read and write IQ-files.
Welle.io is still in beta, but it works much better and decodes better. It is also possible to display quite a lot of additional debugging information:
But welle.io is not able to work with iq-files yet, so we will use Qt-dab.
For testing, I uploaded 3 files to cloud.mail.ru, each contains a minute record of the DAB multiplex, the file size is about 500 MB (this is the size of IQ records for SDR with a 2.4 MHz bandwidth). You can open files in Qt-dab, the download link for which is given above.
File-1 : DAB-8A.sdr - cloud.mail.ru/public/97hr/2QjuURtDq . Multiplex 8A operates at 195.136 MHz and contains 16 stations. The bitrate of all stations is 64Kbps.
File-2 : DAB-11A.sdr - cloud.mail.ru/public/3VVR/2mvjUjKQD . Multiplex 11A at a frequency of 216.928 MHz. It contains 6 stations, with bit rates of 48, 48, 48, 48, 64 and 48KBps, respectively.
File-3 : DAB-11C.sdr - cloud.mail.ru/public/3pHT/2qM4dTK4s . Multiplex 11C at a frequency of 220.352 MHz, also contains 16 stations. The bitrates of all stations are respectively: 80, 80, 80, 80, 56, 96, 80, 64, 56, 48, 64, 64, 64, 96, 80 and 64Kbps.
As you can see, there are no problems with the number of stations, but the main problem is the low bitrate. As for the content itself, the tastes are different and I will not discuss it, those who wish can download the files and listen on their own. The records are not all multiplexes, but the general idea, I hope, is clear.
If we talk about the prospects of digital broadcasting, then they are, alas, rather sad. The main advantage of DAB is more efficient use of the spectrum, which allows you to place more stations on the air. In this regard, DAB + makes sense only for those cities where there is no free space in FM. For Russia, this is probably only Moscow and St. Petersburg, in all other cities there are no such problems.
As for the sound quality, technically, DAB + can provide a bitrate of up to 192Kbps, which will give almost a HiFi sound. In practice, as we see above, broadcasters save and do not go over the bar even at 100Kbps. Of the three multiplexes, there was only one (!) Station broadcasting at 96Kbps (and I can’t call broadcasting music from 48kbps to anything other than blasphemy - such broadcasters should be denied a license;). So alas, it is safe to say with 99% that when switching from FM to DAB, the sound quality will be worse than it was . Of course, maybe in other countries the situation is better, but for example, an English review on youtube with the eloquent title Why DAB sounds so BAD . Technically, DAB is good and there are no complaints about it, but economically, “loot won evil”. A practical conclusion follows from this: even if the test broadcast starts in DAB +, you should not immediately go to the store for a new receiver, most likely the sound quality will be worse than in FM.
Coming back to Russia, is it worth bothering to start broadcasting in DAB? From the point of view of international prestige, probably yes, in order not to look like a backward third world country in the eyes of neighbors, and as a bonus so that cars and radios bought in Europe can fully receive all stations. But from the point of view of the listeners and the sound quality, most likely, users will not get any advantages in either sound quality or content quality.
Of course, DAB has its advantages. This is a lower entry threshold (you do not need to buy your transmitter), a lower cost of equipment maintenance and electricity payments (it is easier to maintain 1 multiplex transmitter than 16 independent). And it would be justified in the event that there were new broadcasters creating interesting and in-demand content. But whether they will appear, given that we are essentially seeing the era of the sunset of radio and the departure of the audience on the Internet, is difficult to say.
If you think about the long-term prospects, then probably in the future, the radio will be a device with an integrated e-sim card and a subscription toYandex music Spotify or Apple Music when purchased. The future is unique for streaming services and personalized content. How soon this happens, we'll see, time will tell.
In recent years, the introduction of digital radio standard DAB + has been discussed in Russia, Ukraine and Belarus. And if in Russia the process has not yet advanced, in Ukraine and Belarus, it seems, they have already moved on to test broadcasting.
')
How does it work, what are the pros and cons, and is it really necessary? Details under the cut.
Technology
The idea of ​​digital radio began to emerge in the late 80s, when it became clear that there was not enough room for everyone in the usual FM range - in large cities the free spectrum in the range of 88-108 MHz was exhausted. In this regard, DAB was considered a good alternative - it is a digital standard in which, due to more efficient coding, more stations can be placed. In the first version of DAB, the MP2 codec was used, in the second version (DAB +) the newer HE-AAC. By itself, the standard by modern standards is very old - the first station DAB earned in 1995, and the station DAB + in 2007m. Moreover, the “age” of the standard is in this case even more likely than a minus - now there is no problem to buy a radio for every taste and budget.
DAB differs from the usual FM quite a lot. And the point is not that one is a “figure”, but the other is an “analog”. The very principle of content transfer is different. In FM, each station broadcasts independently, and in DAB + all stations are combined into a “multiplex”, each of which can have up to 16 stations. There are different frequency channels, so different countries can choose those that are free from other services.
From a business point of view, this difference raises a number of disputes among broadcasters about how to broadcast in multiplex. Previously, the broadcasters themselves obtained a license for the frequency, bought an antenna and a transmitter, now the license will be issued to the multiplex operator, and he will already rent channels to radio stations. Better or worse, it is difficult to say, it is more convenient for someone to have everything of their own, someone is more comfortable for renting.
By the way, in this regard, DAB has a huge and fat minus for the listener - the price of renting a multiplex depends on the bitrate . And if you choose between 192 and 64kbps ... all I think is clear what will be chosen. If broadcasting with poor quality in FM is rather difficult, in DAB it is even economically encouraged (it is clear that this is not the fault of the developers of the standard, but nonetheless). Russian prices are, of course, unknown, while English prices can be found here for an example.
From a technical point of view, DAB + multiplex is a broadband signal, with a spectrum width of about 1.5 MHz, which is clearly visible with an RTL-SDR receiver.
A more detailed description in PDF can be found here .
Competing standards
There are not so many of them. DAB + is used in Europe, HD Radio is popular in the USA, DRM was used in experiments in India, but it's hard to say how they ended.
The map is a bit outdated (in Russia DRM was also tested, but it was abandoned this way), but the general idea can be understood:
A source
Unlike DAB, the creators of the standard HD Radio went the other way - the digital signal is placed directly next to the analog one, which allows broadcasters to use their own antennas and masts.
However, this does not solve the problem, because of which it all began - the problem of lack of empty seats in the spectrum. Yes, and purely geographically (and probably politically), in the ex-CIS countries, the adoption of a European standard looks more logical than using the American standard - the choice of European goods is still more and it is easier to buy receivers. In 2011, there were still references to the Russian RAVIS standard , but everything went out of the way (and thank goodness, since there is no compatible own digital standard with anything, this is the worst that could be thought of for radio listeners).
Testing
Finally, we turn to the practical part, i.e. for testing. In Russia, DAB does not work yet, so we will use SDR records from the Dutch multiplex. Those interested in other countries can also join and send me IQ records, I will process them and make a pivot table.
How can you listen to DAB? Because digital standard, you can decode it using a computer and rtl-sdr receiver. There are two programs - qt-dab and Welle.io , both can work with rtl-sdr.
Qt-dab looks like a student’s coursework, and the author obviously didn’t bother with the design - the fonts don’t fit into the controls, the windows do not scale. But for us the most important thing is that it allows you to read and write IQ-files.
Welle.io is still in beta, but it works much better and decodes better. It is also possible to display quite a lot of additional debugging information:
But welle.io is not able to work with iq-files yet, so we will use Qt-dab.
For testing, I uploaded 3 files to cloud.mail.ru, each contains a minute record of the DAB multiplex, the file size is about 500 MB (this is the size of IQ records for SDR with a 2.4 MHz bandwidth). You can open files in Qt-dab, the download link for which is given above.
File-1 : DAB-8A.sdr - cloud.mail.ru/public/97hr/2QjuURtDq . Multiplex 8A operates at 195.136 MHz and contains 16 stations. The bitrate of all stations is 64Kbps.
File-2 : DAB-11A.sdr - cloud.mail.ru/public/3VVR/2mvjUjKQD . Multiplex 11A at a frequency of 216.928 MHz. It contains 6 stations, with bit rates of 48, 48, 48, 48, 64 and 48KBps, respectively.
File-3 : DAB-11C.sdr - cloud.mail.ru/public/3pHT/2qM4dTK4s . Multiplex 11C at a frequency of 220.352 MHz, also contains 16 stations. The bitrates of all stations are respectively: 80, 80, 80, 80, 56, 96, 80, 64, 56, 48, 64, 64, 64, 96, 80 and 64Kbps.
As you can see, there are no problems with the number of stations, but the main problem is the low bitrate. As for the content itself, the tastes are different and I will not discuss it, those who wish can download the files and listen on their own. The records are not all multiplexes, but the general idea, I hope, is clear.
findings
If we talk about the prospects of digital broadcasting, then they are, alas, rather sad. The main advantage of DAB is more efficient use of the spectrum, which allows you to place more stations on the air. In this regard, DAB + makes sense only for those cities where there is no free space in FM. For Russia, this is probably only Moscow and St. Petersburg, in all other cities there are no such problems.
As for the sound quality, technically, DAB + can provide a bitrate of up to 192Kbps, which will give almost a HiFi sound. In practice, as we see above, broadcasters save and do not go over the bar even at 100Kbps. Of the three multiplexes, there was only one (!) Station broadcasting at 96Kbps (and I can’t call broadcasting music from 48kbps to anything other than blasphemy - such broadcasters should be denied a license;). So alas, it is safe to say with 99% that when switching from FM to DAB, the sound quality will be worse than it was . Of course, maybe in other countries the situation is better, but for example, an English review on youtube with the eloquent title Why DAB sounds so BAD . Technically, DAB is good and there are no complaints about it, but economically, “loot won evil”. A practical conclusion follows from this: even if the test broadcast starts in DAB +, you should not immediately go to the store for a new receiver, most likely the sound quality will be worse than in FM.
Coming back to Russia, is it worth bothering to start broadcasting in DAB? From the point of view of international prestige, probably yes, in order not to look like a backward third world country in the eyes of neighbors, and as a bonus so that cars and radios bought in Europe can fully receive all stations. But from the point of view of the listeners and the sound quality, most likely, users will not get any advantages in either sound quality or content quality.
Of course, DAB has its advantages. This is a lower entry threshold (you do not need to buy your transmitter), a lower cost of equipment maintenance and electricity payments (it is easier to maintain 1 multiplex transmitter than 16 independent). And it would be justified in the event that there were new broadcasters creating interesting and in-demand content. But whether they will appear, given that we are essentially seeing the era of the sunset of radio and the departure of the audience on the Internet, is difficult to say.
If you think about the long-term prospects, then probably in the future, the radio will be a device with an integrated e-sim card and a subscription to
Source: https://habr.com/ru/post/448244/
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