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Live streaming mic/line level problem

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Live streaming mic/line level problem

Postby jszy » Thu Nov 07, 2019 4:43 am

Hi everyone,

I have been streaming music performance on Facebook/Youtube.
However, audio and video sync always seems to be a problem, when using OBS...
So instead of using software, I'm looking into using hardware...

Say I have a stereo audio output that I want to stream (which should be at line level)
If I have a camera with mic input and HDMI out, should I plug the line level audio into the mic input?
Or similarly if I have have an HDMI capture card with mic input, should I plug the line level audio into the mic input?
Will I have to adjust line/mic level in some OBS settings?

Thanks in advance!!
(I don't have such a camera or HDMI capture, so I want answers to these questions before I buy those....lol)
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Re: Live streaming mic/line level problem

Postby Sam Spoons » Thu Nov 07, 2019 11:38 am

Line level and mic level are significantly different with line being maybe 30+dB higher than mic. If you plug a line level signal into a dedicated mic input you would expect to massively overload the mic input*. I suspect you'll need something between the line output and the mic input to match the levels but it may possibly;e to turn the line output and the mic pre gain down enough to get them to work together. AGC in the camera will almost certainly not cope though so you'll need to do it in settings or manually.

* The 'mic inputs' on many pro/semi-pro mixers are designed with a wide enough gain range (sometimes with a 'pad' or attenuator) to accept a line level signal.
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Re: Live streaming mic/line level problem

Postby jszy » Fri Nov 08, 2019 9:13 am

Thanks for telling me that!! Otherwise I might have damaged the camera by using line level audio :lol:

I don't know if an HDMI capture box is considered a mixer though...
Their specs are really baffling too...
Some say "mic in" only...
Some say "stereo in" on the box, but it only shows you pictures of plugging a mic into it....
(for example "gofanco Prophecy USB 3.0 HDMI Video Capture Device with Audio")
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Re: Live streaming mic/line level problem

Postby CS70 » Fri Nov 08, 2019 9:34 am

If you keep the levels down on the mixer and on the camera (gain at 0) you wont likely damage anything - it may work, or you may simply have a crappy, distorted sound as the voltage you send into the microphone will be too much for it to handle without distorting.

The main issue with that setup is that it allows you to easily make a mistake, you're working with very little margin. And in the heat of the action mistakes happen all the time.

The "stereo in" is most likely a line in, so worth trying.

For analog inputs, there are tools called "DI boxes" whose job is to take a line level signal and convert it down to microphone level - so that it can go into a mic input (and be the amplified again to go back to line level..).

It's generally not so great as you're taking amplifying a signal up, down and then up again and each operation adds noise and a little distortion, but kit nowadays tend to be pretty good so the difference can be not so noticeable.
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Re: Live streaming mic/line level problem

Postby jszy » Fri Nov 08, 2019 10:25 am

CS70 wrote:For analog inputs, there are tools called "DI boxes" whose job is to take a line level signal and convert it down to microphone level - so that it can go into a mic input (and be the amplified again to go back to line level..).

It's generally not so great as you're taking amplifying a signal up, down and then up again and each operation adds noise and a little distortion, but kit nowadays tend to be pretty good so the difference can be not so noticeable.

you are right... I'm exactly trying to avoid buying yet another DI box....
I really don't like the concept of turning the signal up and down over and over again...
and I don't want to spend that much lol...
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Re: Live streaming mic/line level problem

Postby CS70 » Fri Nov 08, 2019 10:33 am

Which type of camera format are you looking at? There's many models who have a line in, so you can take whatever stereo output from a mixer or interface and just plug it into the camera.

Also: all of this makes sense if you absolutely need to stream real time.

If not, the best way is to record video and audio totally separated and then sync in post using some transients.
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Re: Live streaming mic/line level problem

Postby jszy » Fri Nov 08, 2019 12:37 pm

CS70 wrote:Which type of camera format are you looking at? There's many models who have a line in, so you can take whatever stereo output from a mixer or interface and just plug it into the camera.

Also: all of this makes sense if you absolutely need to stream real time.

If not, the best way is to record video and audio totally separated and then sync in post using some transients.

I do facebook live music performance most of the time
syncing the audio and video in the streaming software was a hassle....
so, hardware syncing should be the way to go

as for the camera, I still haven't bought a nice one yet (was only using a webcam)
I really didn't know about cameras that have both HDMI out and line in!! Which models would you suggest??
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Re: Live streaming mic/line level problem

Postby CS70 » Fri Nov 08, 2019 5:01 pm

jszy wrote:
CS70 wrote:Which type of camera format are you looking at? There's many models who have a line in, so you can take whatever stereo output from a mixer or interface and just plug it into the camera.

Also: all of this makes sense if you absolutely need to stream real time.

If not, the best way is to record video and audio totally separated and then sync in post using some transients.

I do facebook live music performance most of the time
syncing the audio and video in the streaming software was a hassle....
so, hardware syncing should be the way to go

as for the camera, I still haven't bought a nice one yet (was only using a webcam)
I really didn't know about cameras that have both HDMI out and line in!! Which models would you suggest??

Well never really tried but my GH4 and GH5 have both HDMI out and line in - I think the GH4 has a mic in but it will should work has it has a -12db pad.

Best thing is to bring your mic/preamp to a photo shop and ask.

As of HDMI output, make sure its possible when recording, not only for playback - as that's a limitation with cheaper models.
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