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Topic: AAC 96kbps for DAB test (Read 6417 times) previous topic - next topic
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AAC 96kbps for DAB test

As discussed in this thread, I'm putting together a digital radio listening test.

To represent iBiquity's "HD radio" - the USA's IBOC DAB system - I want to include AAC at 96kbps.

The first question: what encoder should I use? It needs to offer as good quality as possible at 96kbps, and also operate in (at least) real time on current equipment. (A less than real-time encoder isn't going to be used to broadcast live radio!!!)

The second question: It's been suggested that 32kHZ sampling is best at 96kbps with AAC. Does anyone know what sampling rates are used/allowed by the iBiquity USA digital radio system?


The hybrid FM system (which will be used whilever analogue services must be transmitted alongside digital ones) uses 96kbps AAC - this is stated in several places. However, I can't find any data on sampling rates. Also, I'm sure I've read that, once the analogue service is switched off, the digital service can change to 128kbps AAC - but I can't find confirmation of this anywhere. I can't find any information about the bitrates used on the iBiquity hybrid AM system, which is not the same thing as Digital Radio Mondiale.


So, if you can shed any light on the matter - please do!

Cheers,
David.

AAC 96kbps for DAB test

Reply #1 –
Quote
The first question: what encoder should I use? It needs to offer as good quality as possible at 96kbps, and also operate in (at least) real time on current equipment. (A less than real-time encoder isn't going to be used to broadcast live radio!!!)

Maybe you should take a look at the solutions offered by Mayah and Telos. Besides, what do you mean by "current equipment"? You can archive realtime with any AAC encoder, given you have enough horse power.

Quote
The second question: It's been suggested that 32kHZ sampling is best at 96kbps with AAC. Does anyone know what sampling rates are used/allowed by the iBiquity USA digital radio system?


The hybrid FM system (which will be used whilever analogue services must be transmitted alongside digital ones) uses 96kbps AAC - this is stated in several places. However, I can't find any data on sampling rates. Also, I'm sure I've read that, once the analogue service is switched off, the digital service can change to 128kbps AAC - but I can't find confirmation of this anywhere. I can't find any information about the bitrates used on the iBiquity hybrid AM system, which is not the same thing as Digital Radio Mondiale.


Have you tried contacting iBiquity?

Regards;

Roberto.

AAC 96kbps for DAB test

Reply #2 –
Quote
Maybe you should take a look at the solutions offered by Mayah and Telos.

Quote
The second question: It's been suggested that 32kHZ sampling is best at 96kbps with AAC. Does anyone know what sampling rates are used/allowed by the iBiquity USA digital radio system?


The hybrid FM system (which will be used whilever analogue services must be transmitted alongside digital ones) uses 96kbps AAC - this is stated in several places. However, I can't find any data on sampling rates. Also, I'm sure I've read that, once the analogue service is switched off, the digital service can change to 128kbps AAC - but I can't find confirmation of this anywhere. I can't find any information about the bitrates used on the iBiquity hybrid AM system, which is not the same thing as Digital Radio Mondiale.


Regards;

Roberto.

Are these significantly better than the software codecs often discussed here (e.g. Ivan's encoder, Apple's encoder, FhG's encoder)?

Quote
Besides, what do you mean by "current equipment"? You can archive realtime with any AAC encoder, given you have enough horse power.


I'm assuming a radio station wants to broadcast live using an encoder which doesn't cost the earth, and sits nicely in a 19" rack unit. I don't want to use a hardware solution for my test, but I don't want to use a software solution that's so slow that it's not going to make it into the broadcast environment. I'm looking for a good software solution that (hypothetically) could run real-time in a stand-alone hardware box (even if that box was really a PC). I didn't realise that all AAC software encoders could do this easily.


Quote
Have you tried contacting iBiquity?


I'll try that. I know it's the obvious thing to do, but I haven't had luck with similar contacts in the past.

It's amazing the information doesn't seem to be on the web anywhere. You could almost build a Eureka 147 DAB system from the info on-line, whereas the IBOC details have elluded me. I was hoping someone else had some links.

Cheers,
David.

AAC 96kbps for DAB test

Reply #3 –
Quote
Are these significantly better than the software codecs often discussed here (e.g. Ivan's encoder, Apple's encoder, FhG's encoder)?

They are significantly worse.

Mayah is worse because it's very old, and tweaked for real-time encoding on old equipment (400mHz)

Telos is worse because of hardware encoding constraints.

I posted them here not because of their quality, but because up to some time ago they were the only legal solutions for AAC real-time encoding (AFAIK).

Quote
I'm assuming a radio station wants to broadcast live using an encoder which doesn't cost the earth, and sits nicely in a 19" rack unit. I don't want to use a hardware solution for my test, but I don't want to use a software solution that's so slow that it's not going to make it into the broadcast environment. I'm looking for a good software solution that (hypothetically) could run real-time in a stand-alone hardware box (even if that box was really a PC). I didn't realise that all AAC software encoders could do this easily.


I recommend Psytel Fastenc then. It's available at RareWares. You can get real time encoding with less than 500 mHz on x86.

Regards;

Roberto.

AAC 96kbps for DAB test

Reply #4 –
Quote
I recommend Psytel Fastenc then. It's available at RareWares. You can get real time encoding with less than 500 mHz on x86.

Then he would have to do the resampling to 32 kHz outside of the codec first with SSRC or something similar which would eliminate the advantage of FastEnc's double speed compared to AACEnc. The sound without resampling at 96 kbps can be sufficient depending on the test samples, but I wouldn't use it in general.

If it has to be "fast", I would either recommend Nero AAC (almost the same speed as PsyTEL FastEnc) or QuickTime 6.1, both codecs use 32 kHz resampling at 96 kbps automatically, as far as I know.

By the way, if the computer is fast enough, I would also include AACEnc, because I liked the sound of the -internet preset with an additional resampling at 32 kHz a little bit better than a CBR of 96 kbps from either PsyTEL, Nero or QuickTime (only a short test with one sample). But I think I've mentioned that already in the other thread...
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AAC 96kbps for DAB test

Reply #5 –
OK, my concerns are quality first, speed second - as long as the speed is fast enough for real-time encoding on current hardware. Sorry if I'm not explaining myself very well.

However...

I contacted iBiquity, and they promptly replied with all the information I requested...

FM Hybrid mode:
PAC audio codec
96kbps 44.1kHz

AM Hybrid mode:
PAC audio codec
36kbps 44.1kHz


Now, I've come accross this before: some sources say IBOC uses AAC, others say PAC. Bell Labs / Lucent developed PAC. Here, they compare it with AAC:
http://www.lucent.com/press/1098/981014.cob.html

The most recent official sources all mention PAC, rather than AAC. So, it would seem my initial information was incorrect, and I'm going to have to go and talk to Lucent.

Cheers,
David.

AAC 96kbps for DAB test

Reply #6 –
Quote
The most recent official sources all mention PAC, rather than AAC. So, it would seem my initial information was incorrect, and I'm going to have to go and talk to Lucent.

Have you tried the AudioVeda encoder? It's the latest PAC encoder, AFAIK. (released, that is)

AAC 96kbps for DAB test

Reply #7 –
Quote
Have you tried the AudioVeda encoder? It's the latest PAC encoder, AFAIK. (released, that is)

I hadn't heard of it - and now I have it, I can't make it work. The company has vanished, so (obviously) their product registration no longer works, and I can't find another way in.

I'm wondering what the difference between PAC and ePAC is. (yes, I know, "enhanced").

The only other interesting information I could find was
http://mpeg.telecomitalialab.com/faq/mp2-a.../mp2-aud.htm#58

Maybe that's why the codec is so elusive? Maybe not.

Cheers,
David.

AAC 96kbps for DAB test

Reply #8 –
Quote
I hadn't heard of it - and now I have it, I can't make it work. The company has vanished, so (obviously) their product registration no longer works, and I can't find another way in.

Haha. it's easy. You need to put the right information in the windows registry, and it will believe you registered the program.

Unfortunately, I have this registry patch at home, and I will only return there Sunday.

If you want, I can e-mail it for you as soon as I get there. If you do, PM me your mail address.

Regards;

Roberto.

AAC 96kbps for DAB test

Reply #9 –
Quote
I'm wondering what the difference between PAC and ePAC is. (yes, I know, "enhanced").

I have an old PAC encoder (audiolib 1.0), you can try it to check out the "enhancements" in ePAC.

And, of course, you can try out Astrid AAC to check quality of old PAC encodings.

Quote
Maybe that's why the codec is so elusive? Maybe not.


I think it's elusive because Lucent never published specifications, and they only once licensed it for software implementations, to VedaLabs (former CelestialTech). That's why nearly noone knows it.

AAC 96kbps for DAB test

Reply #10 –
Quote
If it has to be "fast", I would either recommend Nero AAC (almost the same speed as PsyTEL FastEnc) or QuickTime 6.1, both codecs use 32 kHz resampling at 96 kbps automatically, as far as I know.


Actually, latest version of the plug-in on "medium quality" is way faster than old fastenc.

Quote
By the way, if the computer is fast enough, I would also include AACEnc, because I liked the sound of the -internet preset with an additional resampling at 32 kHz a little bit better than a CBR of 96 kbps from either PsyTEL, Nero or QuickTime (only a short test with one sample). But I think I've mentioned that already in the other thread...


Nero AAC plug-in also has internet preset

AAC 96kbps for DAB test

Reply #11 –
Quote from: 2Bdecided on
To represent iBiquity's "HD radio" - the USA's IBOC DAB system - I want to include AAC at 96kbps.

  ...
The second question: It's been suggested that 32kHZ sampling is best at 96kbps with AAC. Does anyone know what sampling rates are used/allowed by the iBiquity USA digital radio system?

This is a bit old, but I was searching..

From what I've read/heard, the response is supposed to go to 20 khz (able or enforced?), so probably 44 khz sampling.

As to the bit rate, the big draw seems to be alternate program channels, so if you have 2 that's 48 kb/s, unless they can give one program more bits when one is voice and one is music.