Stereo Tool

Hi,
we have a DAB+ Radio with a very low bitrate of just 30 kbit/s with the HE AACv2 Codec and I'm trying to get it to sound good with Stereo Tool.

I've seen there are quite a few things to consider with AAC Plus v2 (viewtopic.php?t=52), but unfortunately there is no preset available for the current version of Stereo Tool (7.84) and I'm not sure how to get it to sound better.

I mainly have a problem with high frequencies, which sound extremely harsh and really bad. (This probably has to do with SBR as I was able to find out)

Here is a short recording I made how it sounds on the radio which uses HE AACv2 with 30kbit/s: https://www.dropbox.com/s/8ds72pvdgwkzy ... o.ogg?dl=0.
Here is also a short clip from the web stream where it sounds good. No problem there. (This is a 320k MP3-Stream) https://www.dropbox.com/s/myn474hibayki ... m.mp3?dl=0
Here is the Stereo Tool Preset which I'm currently using: https://www.dropbox.com/s/yemw02792ftac ... o.sts?dl=0

The radio station has about 70% talking, 30% music in general.

Would somebody be able to help me getting it to sound good, or would somebody have a preset which works good for low bitrates on DAB+?

Thanks!
Michael

What exactly is that?

It does not sound like AAC at only ~30kbps.

How this sounds to you?
http://85.25.73.243:10680/

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The web stream is 320k MP3, what sounds bad is the DAB+ radio.
https://www.dropbox.com/s/8ds72pvdgwkzy ... o.ogg?dl=0. This one sounds bad.

Your stream sounds good for 32k, better than what I get with 30k over DAB+ it seems. Although the highs still seem a bit harsh and the artefacts would be especially noticeable when there's just speech.

well i just changed to "other" AAC codec. AAC Plus v2. And it;s bit better.
I dont know what you can expect more form 32kbps. This just cannot be better.
Also why/how 30 and not 32 or 28 ?

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Yes, now it sounds much better!

What are you using to encode it? ffmpeg? I've tried re-encoding our high quality stream myself with ffmpeg but it didn't sound as good as your stream does now.

It's 30k because we have 66 Capacity Units (CU) on our local DAB+ Multiplex which we have divided onto two radio stations
Station 1: 24 CU*1.33 = 31.92 kbit/s (Total Bitrate) – 1.7 kbit/s (for DAB+ Data stream) = 30.22 kbit/s left for Audio (station has mostly speech)
Station 2: 48 CU*1.33 = 63.84 kbit/s (Total Bitrate) - 5.4 kbit/s (for DAB+ Data stream) = 58.44 kbit/s left for Audio (station has mostly music)

Would it also be possible for you to send me the Stereo Tool Settings you're using? Would you have any tips on optimisations for speech?

That's new preset i'm working on last few weeks. Still in very beta! Should be ok with speech too, yet still need to check that!
Anyway here it is.. Set LPF to 16.5kHz (in preset it's at 15.5)
Stream is Opticodec LE AAC Plus v2 32kbps.

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Thanks, it turned out that Parametric Stereo wasn't enabled on the encoder, so it sounded like HE AAC v1 and not HE AAC v2 which sounds much better at that bitrate.
Your preset sounds great with speech, by the way.

@michaelnachname - I'm interested in clarifying something - are you encoding a bit stream at site (studio) or sending audio to a DAB+ multiplex for encoding? (Are you delivering the 320 kbps MP3 stream as an audio source for this?)

I just got a new idea for a filter that might be able to optimize processed audio for lossy codecs. Will add it to my todo list!