No voice audio when capturing VCR audio via Focusrite interface. Why?

[AlvinusDeDiaspar]

This is a strange effect which I'm sure has a cogent explanation.

I am running some experiments capturing VCR audio. I'm playing the movie Flubber from a commercial VHS tape.

Video is traveling on S-Video to a Hauppauge capture device, while the audio is going from the L and R RCA ports in the VCR's back to the interface's input jack (via a stereo 6.3->3.5mm adapter). I'm using one of these for driving those 2 signals to the Focusrite:
https://www.wetu.pl/images/p/7/4/2/mini/550px_7423.webp

Independently analyzed, L carries voice+music, while R only carries music.

Now, if I connect both R and L, the voices of the actors are reduced to a whisper, while the music track is loud and clear. If I unplug R, both the voice and the sound are heard clearly.

I suspect both signals are being added and the voice amplitude is being proportionally reduced. Correct me if I'm wrong.

How to configure this set-up in such a way that I can plug both cables and can get both voice and music in Amarec?

Thanks!

[betwixt]

It sounds like one channel is inverted but I'm not sure what configuration would change that. It's the effect you get when a sound, voice in this case, is on both channels but different OTHER sounds are on L and R. If they are added to make a mono sound, the common sounds to both channels cancel out but differences are still there.

There is another possibility, there is a short circuit in the adapter and the channels are connected together, the impedances will be wrong and maybe the dominant channel is suppressing the other one. A testmeter should confirm that if you have one. Plug the 3.5mm jack into the socket (in case it fits badly and that is causing the short) then measure resistance (Ohms) between the center pins of the RCA plugs, it should be greater than or equal to about 2,000 Ohms but no less.

Brian.

[AlvinusDeDiaspar]

I'll do that experiment tomorrow.

For the record, though, the fact is that:
1. L is outputting music+voice (so, the full sound of the movie)
2. R is outputting just the music, without the voice

That's why I was picturing the possibility that, if both signals are added, you'll end up with: music + music + voice, and the voice will have half the amplitude.

[timtape]

Unusual to have the full mix on one channel and just the music on the other. Usually it's the mono mix on both or a stereo mix across both.

[AlvinusDeDiaspar]

It's a dubbed tape (Polish).

I've tried with a cheaper 6.3->3.5 adapter and the behavior is the same. Also with another RCA->3.5mm jack adapter. No change.

The issue is solved when unplugging R. Then the voice's volume goes up relative to the music track.

Strange stuff indeed.

[timtape]

I'd just use the left track then.

[mistrydan]

Hey AlvinusDeDiaspar, If you combine both signals, the voice might become quieter. This often happens when one of the channels is reversed.

Make sure all the wires are plugged in correctly. Sometimes, messing up the connection can mess with the signal.
You can also measure the resistance between the centers of the RCA plugs. It should be at least 2000 ohms. If it's less than that, there might be a short circuit.

If you can, record the sound from just one channel and listen. That way, we can figure out where the problem is.