We are having a problem with audio quality coming through the Wowza streaming engine. All audio loses frequency above 13khz. We understand that most human beings do not readily hear distinct sounds in that frequency, but many of the artists streaming through our service do indeed notice the issue. We have tried different configuration settings in “transcode.xml”, changing the “PassThru” and changing bitrate, but nothing seems to help - except turning off transcoding altogether, which doesn’t see a reasonable option. Aside from audio bitrate and codec, are there any other configuration options we can try? What might be causing this “low pass filter” effect? It should be possible to get some AAC audio that does not lose the higher end of the spectrum all the time.
All ideas welcome - we’re on the cusp of searching for other solutions…
Let me see what I can find out for you… have you already submitted a support ticket so our engineers could investigate? It may be an issue we could easily detect and help you correct or make some suggestions.
Hi, Rose. Thanks for getting back to us. I don’t think we have submitted a ticket yet. Unfortunately, I am a contractor, and do not yet know the necessary client credentials with which to submit a ticket. I will check on that and get back…
In the meantime, are there any audio parameters other than bit rate and codec, that might affect this, that I can experiment with?
Thanks!
Yes there are @David_Arndt and here is the doc with some examples:
https://www.wowza.com/docs/how-to-control-transcoded-audio-with-audio-encoding-parameters
You may also get a pretty quick answer in our public slack where there’s streaming engineers from all over the world. I can tag @Karel_Boek in here as well, who is one of our Streaming Experts to see if he has suggestions in addition to the article I shared. As far as submitting a ticket, you’re right it would be who started the account, but they can add people to the tech support conversation upon request without having full access the media server.
I’ll also ask tech support if they have any advice and come back and post what I’m told.
Hope it all works out for you!
Tech support is asking if this is AAC in and out @David_Arndt? They also want to know “source config, A+V or V only, are they transcoding or transrating the audio, etc.” They also want to know if you’re using HE-AAC or AAC-LC.
They did say that if ffmpeg notes that the libfdk_aac defaults to a low-pass filter of around 14kHz. There is a switch to allow higher if needed. If you’re using ffmpeg.
They’ve never heard of anyone having this issue before they said.
Thanks…
It should be AAC in - transcoding is set to AAC out. The source is audio + video. I know that we are using ffmpeg to replay saved video, but I assume not for live streams. Regardless, if I use ffmpeg with our production parameters to stream to a file, the fidelity in the file is unchanged (i.e., no low pass filter).