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Normal Output vs FM Output
https://forums.stereotool.com/viewtopic.php?f=3&t=32767
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Author:  Radio Quack [ Wed Jun 01, 2022 12:09 pm ]
Post subject:  Normal Output vs FM Output

Hi

I am using ST for streaming purposes only and I have the HifiBerry DAC+ADC Pro to receive analogue line in audio for ST to process. I use a sampling rate of 48Khz.

At the moment, the Normal Output in ST provides a feed to the Alsa loopback so Liquidsoap can pick up the audio from the loopback for encoding before sending it to icecast (320K AAC 48Khz)

I was struggling to be able to have any kind of additional audio feed to my Hifi because I wasn't able to use the spare RCA line outs for some reason, however, I discovered I could if I use FM output.

I then swapped Normal Output and FM Output - so that Alsa Loopback/Liquidsoap receives audio from FM Output whilst Normal Output feeds to the Hifi.

Sadly this failed! FM Output complained of a sampling error! For some reason FM Output didn't like being fed to the Alsa Loopback. Also pulseaudio is already configured for 48khz so is there a mismatch with FM Output?

Why would this be? What's the difference between Normal and FM output? I do not use any of the FM processing features, I just happened to find that it was the only way to get audio coming out of the HifiBerry RCA line out jacks to my Hifi.

I have reverted back to how it was for now.

Ideally the hifi should receive the best quality audio, it matters less so for the feed to liquidsoap as long as it's 48khz sampling rate and good for the 320K AAC output for icecast.

Maybe it would be nice to have a second normal output to use? Sadly, the low latency output stutters too much, even with the lowest settings!

Any ideas would be welcome!

Author:  MrKlorox [ Wed Jun 01, 2022 5:13 pm ]
Post subject:  Re: Normal Output vs FM Output

The Low latency output is of a much lower quality anyway. I only use it for hearing my own microphone in voice chat.

What version number is this happening in? I've switched back to the stand-alone version in windows for the time being to try out the new GUI.

I've been using an optical I/O device as ASIO on the second input and FM Output, also without any FM licensing. And they perform better than the non-ASIO devices I use as the primary/normal output. So I don't think there should be any significant difference between FM and Normal as long as none of the Transmitter settings are enabled (or it'll want 192khz, etc). There are some filters like the Advanced Clipper that change slightly when FM Output is enabled, but that shouldn't make your buffering/stuttering worse.

Author:  Radio Quack [ Wed Jun 01, 2022 8:12 pm ]
Post subject:  Re: Normal Output vs FM Output

Thanks!

I'm using v9.90

I can't try out the new GUI yet until a version is compiled for 64-bit ARM.

What you say makes a lot of sense to me. I just wish I knew why using FM output would throw an error about the sampling rate. It's strange, I have all the FM transmitter related stuff turned off as I'm only streaming with this.

Luckily it's only the low latency output that stutters, both normal and FM outputs sound fine at the moment. From what you say, it sounds like I'm not missing very much here!

Just wish I could use FM output for Liquidsoap so I have more flexibility with the normal output which let's me switch to unprocessed sound etc.

Author:  MrKlorox [ Sat Jun 11, 2022 4:09 pm ]
Post subject:  Re: Normal Output vs FM Output

Quote:
I'm using v9.90
Have you tried this in 9.91? If FM Output still doesn't work while both Transmitters are disabled at 48khz, you might want to post the issue in the next beta/release thread.

Author:  Radio Quack [ Sun Jun 12, 2022 9:45 pm ]
Post subject:  Re: Normal Output vs FM Output

Quote:
Quote:
I'm using v9.90
Have you tried this in 9.91? If FM Output still doesn't work while both Transmitters are disabled at 48khz, you might want to post the issue in the next beta/release thread.
Hi!

Thanks for your reply :-)

I didn't realise that 9.91 had been released and I can see they have the ARM64 version available. I will give it a try and see what happens :-)

Update: I have the same problem with v9.91. I have posted to the v9.91 thread. Thanks again for your suggestion!

Author:  gjbbgu [ Mon Jun 13, 2022 9:42 am ]
Post subject:  Re: Normal Output vs FM Output

Quote:
Why would this be?
fm output runs at 192 kHz so that's why it doesn't work.

if you run jack you will be able to do what you want.

Author:  Radio Quack [ Mon Jun 13, 2022 10:15 am ]
Post subject:  Re: Normal Output vs FM Output

Quote:
Quote:
Why would this be?
fm output runs at 192 kHz so that's why it doesn't work.

if you run jack you will be able to do what you want.
Thanks!

I tried to use jack in the beginning but I had a lot of trouble with it. I did get it to work lately but some strange GUI quirk prevented me from ensuring I could change both left and right input channels on ST - I was hoping to use jack to route the audio to another Raspberry Pi for the encoding and streaming.

Author:  MrKlorox [ Tue Jun 14, 2022 8:34 pm ]
Post subject:  Re: Normal Output vs FM Output

Quote:
fm output runs at 192 kHz so that's why it doesn't work.
For me, in the new GUI at least, FM Output works on my 48khz ASIO card in Win64. It's only when I try to enable the FM Transmitter that it gives me the error about needing the higher sampling rate. This is fine because I don't have an FM license or need any FM processing.

Am I the one experiencing the unexpected behavior?

I think it's handy as heck to be able to use 2 outputs (headphones and speakers), in addition to being able to stream via Icecast to my phone, without needing an audio device capable of 192khz. I hope this behavior is standardized across all versions.

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