Audio crackle/scratch only when using clean HDMI out with a long cable from mic to 90D

[monfresh]

Hello,

I have a strange issue that only started happening recently with my 90D (bought new from Canon in 2020). Up until a few weeks ago, I had been happily recording video and audio with this setup:

Rode VideoMic NTG plugged into 90D via the Rode SC8 3.5mm TRS cable (20ft)

Camera set to Clean HDMI 4K output and connected via an Elgato CamLink 4K either directly to my MacBook Air M4 or to my Apple Studio Display. I have the following relevant settings on the camera:

Sound set to manual and the level at one notch above zero
Attenuator: disabled
WiFi and Bluetooth: both disabled

Camera is powered by the AC-E6N adapter

Recently, the audio output started becoming scratchy/crackly. After trying every possible thing I could think of (different cables, different computer ports, different laptops, different software for capturing video/audio, different Mics, bought a new CamLink, plugged camera into different outlets, turned off Bluetooth and WiFi on my phone and laptop), these are the only 2 scenarios where the audio is clean:

1) With clean HDMI out: when the Rode mic is connected to the camera with a relatively short cable, such as the Rode SC10 TRRS to TRRS cable the VideoMic came with (yes, TRRS, not TRS), or another short TRS to TRS cable, in this case the 4-foot Anker 3.5mm Nylon Braided Auxiliary Audio Cable

2) Without HDMI (HDMI cable unplugged): when recording directly to the SD card, and Rode VideoMic plugged in with the long (20ft) SC8 TRS cable (not TRRS)

Based on the results of the first scenario, one would hypothesize that clean HDMI out only works with audio cables of a certain length. The Rode SC8 is supposedly shielded, and I also tried another 20-ft TRS to TRS cable from Ruaeoda that I got from Amazon. Both resulted in crackles, but only when using HDMI out. When recording directly to the SD card, the audio is clean, so that would imply the audio cable is not the issue.

Has anyone else come across this issue when using clean HDMI out when using a long audio cable from a microphone to the 90D? If not, what cable and length are you using, and with what microphone? What video capture hardware are you using and with what kind of computer?

The strange thing is that this used to work fine. Something happened recently that is now causing this crackle issue 100% of the time when using clean HDMI out with a long audio cable.

Any thoughts would be greatly appreciated.

[AtticusLake]

Hi,

sorry to hear about your problem, and I'm afraid I don't have any direct answer for you. Noise issues can be devilishly tricky to pin down, and it sounds to me like you have several factors conspiring together to cause the issue -- the audio cable and the HDMI, at least.

However, I do think you're on the right track to be looking at the audio cable. The audio connection you're using is unbalanced -- that means there's one signal wire for audio. So a typical TRS mini-jack has two signals, for stereo, plus ground. This arrangement gives you no protection against noise, and it's generally not a good idea to use a long cable (like over a metre). Your 20ft audio cable is basically a giant aerial picking up any and all electrical noise around -- the fact that it's a Rode official part makes no difference. It may be screened, but that's only a band-aid on the issue.

This is why professional audio uses balanced connections, typically using XLR plugs. This gives you two signal wires for each signal; so a 3-pin XLR plug is only mono: two signal wires for ONE channel, plus ground. The balanced connection largely cancels out noise, and you can run cables for long distances.

I made a video explaining the different connection types, if you're interested: https://moonblink.info/FieldRecording/content/course#Connections

As for why this has started happening recently, it may be that something in your camera has changed. Maybe a capacitor has drifted out of spec, making it more vulnerable to noise. Or maybe something near you has started generating electrical noise. Any new electrical machinery nearby, for example.

As for what you can do about it... I wish I had some good ideas. I do think that the long unbalanced audio cable is a prime suspect. However, you can't just change over to balanced. A balanced connection is only balanced if the WHOLE connection is balanced -- i.e. the microphone, the cable, and the audio input. Since your camera doesn't have a balanced input, that's no good. Adapting between balanced and unbalanced connections with a simple plug adapter cam be problematic, and won't give you the benefits of balanced.

You could change over to recording separate audio -- i.e. get a balanced mic, and an audio recorder, and sync sound in post. But that's a lot of hassle.

Replacing the audio cable with a wireless connection could help; but then again, it could introduce interference problems of its own. There are numerous wireless systems that work on the 2.4GHz band, and these don't cost much; or you could consider Sennheiser's AVX system, which works on a different band, and hence avoids a lot of that interference. I reviewed that system, in case you're interested: https://moonblink.info/MudLake/gear#AVX

Anyway, like I said, that doesn't seem like much help, but hopefully it's shed a little light.

[monfresh]

Thank you! That's helpful.

My next steps were going to be to first try a premium Monoprice 15-ft 3.5mm cable (20AWG), and if that doesn't work, then try a 6.6ft USB-C cable to plug the mic directly into my computer, and then sync up the audio if necessary.

That shouldn't be too much additional hassle since I will be using ScreenFlow to capture the video anyway and to adjust the audio levels. I can clap at the beginning and then presumably I would only need to line that up, and then everything else should be lined up.

[AtticusLake]

Glad to help.

My guess is that a new cable won't help -- premium or not, it's still a long copper wire plugged into your camera.  Sync audio, OTOH, should be fine; if the hassle isn't too much, then go for it.   You may find it gives you more versatility.

Personally I started out with wired audio, and found the wire to be a huge hassle; I switched to wireless, and haven't looked back.

[monfresh · Accepted solution]

I figured it out! It was my left speaker.

Here are the results of my tests. In all these tests, the speakers (Dynaudio BM5A) are plugged into power strips but powered off. 

- When both speakers are plugged into my MOTU M2 audio interface via an XLR to 1/4" Mogami cable, noise is present.

- When I unplug just the left speaker from the MOTU, the noise disappears

- If also unplug the XLR end from the left speaker, the noise comes back

- I switched the XLR to 1/4" cables (what used to be on the right speaker is now on the left speaker and vice versa), and I get the same results where it's only the left speaker that generates noise when plugged into the MOTU

- If I leave the speakers connected to the MOTU but remove the power plug from the back of both speakers, the noise remains. If I unplug the left speaker from the MOTU, the noise remains! Then if I put the power cord back on the right speaker only, the noise remains, but when I put the power cord back into the left speaker as well, the noise disappears. Note that at this point, both speakers are plugged into 2 different power strips that both go into the same wall outlet pair.

- If I unplug the left speaker from its original power strip and plug it into the other power strip where the right speaker is plugged in, then the noise comes back, even when the left speaker is not plugged into the MOTU. As soon as I unplug the left speaker from the new power strip and plug it back into its original power strip, the noise disappears.

I hope this might help someone! And if someone can explain what's going on here, that would be awesome.