Anytime I record video on the Canon R7 if one channel is unused there is digital data style noise that appears faintly in the recording.
How I came about it:
Initially I found this when I purchased a tascam CA-XLR2d-C adapter and thought it was the adapter that was the problem. It did not matter which channel (left or right) was unused you could hear the digital noise on the "empty" track. I then removed that adapter and tried several mics directly into the mic jack on the R7 with the same results. If the mic is set up to record to both channels there is no problem. If you only have it connected to one channel you get the noise.
I did try changing the settings such as from 4k down to FHD and 60 to 24fps with no change.
Can anyone else perform this test and see if you have the same problem? I did update the camera to the latest firmware.
I have a sample of it uploaded to youtube but not sure if the canon forum allows links.
If you can, try shorting out (with a jumper or jumper plug) the unused channel. An unloaded mic input can cause noise to be recorded. Also, a stereo to mono adaptor cable will cause one mic signal to be supplied to both left and right mic inputs simultaneously and should eliminate the problem.
Grounding the unused input would be an interesting test. However, you should be able to turn a mic down without causing the issue. This issue recreated with the mic unplugged or with the secondary mic turned all the way down in the case of the tascam adapter. Since this leads me to believe its something the camera is doing at a software level that is not handling the one channel to have zero input. I will try grounding out the unused channel as a test when I get back from vacation. Since it happened with both the built in mic jack and the tascam adapter through the digital shoe it tells me its not a DAC issue. The stereo to mono adapter would solve the issue of a single mic but would not solve the issue if you were recording two mics and while recording wanted to turn down/off the second mic. However, you should also be able to just plug in a lav mic without having an adapter so while there are work arounds it would be nice to confirm if others can recreate the scenario and if so have canon investigate/fix the issue.
To narrow down the issue, which mic are you connecting to the R7 directly and how specifically? When I connect my Rode lav II mic directly to my R5, it records to both LR channels. When using external mics, I always avoid using auto and set it to manual as Canon's DAC aren't the best and boost the signal from the mic side (both my Rode mics allow to boost signal in order to minimize the gain in the camera itself).
The voice side is very clear and this is very easy to fix in post by splitting the channels and selecting which channel you want to use (process will vary on editor you use).
My test started with a Shure SM58 connected via xlr through the tascam CA-XLR2d-C with the tascam adapter set to two mic mode. You could recreate it on either left or right. I then used a Rode reporter mic with the same results confirming that it was not mic specific. If both channels had some input then there was no noise but if one channel was turned all the way down you got the digital noise. This led me to believe it was a bug or incompatibility with the tascam digital adapter and the R7. However, I then removed the adapter and tried the same scenario with a couple of Lav mics connected directly to the R7 mic input jack. I had manually set the R7 mic input to confirm the auto mode was not the issue. When that gave the same problem it eliminated the tascam adapter and then narrowed it down to the camera itself. This can not be an issue with the R7 DAC because the tascam adapter has its own DAC and sends the audio via data through the hotshoe I believe. I tested a rode video mic as well and it had confirmed the same. If the rode is connected as normal there is no problems since its a stereo feed. If you connect up a stereo to mono splitter and connect up the rode to one of the split channels you get the noise on the unused channel. My guess at this point is the camera's software is introducing this and doesn't know how to handle a channel that has no input. I haven't had the chance to try the other persons test where the suggestion was to ground the unused mic signal and that seems like it could be valid to discover if there is a change in behavior however in normal use you should be able to cut someones mic while recording without introducing the noise. I'll be out of town for a bit so I won't be able to try that until I return.
The unused channel's built-in compressor is raising the gain to a high level to try to raise the non-existent mic signal, thus causing the noise. At least that is what I perceive it to be doing.
In the 5D IV manual, it cautions against using WIFI while recording as it can cause noise on the audio recording. Do you have WIFI on while recording?
I got a chance to try new tests tonight. Wifi and bluetooth are turned off. Airplane mode is on. The noise on the empty channel remains. I then used a 3.5mm splitter that splits the tip and ring into a left and right jack. I plugged the lav mic on one side and on the other side I plugged a 3.5mm cable where I shorted both tip and ring to ground. Therefore the empty channel was grounded. The digital noise remained. It would appear at this point there are no other options to try. This must be something in firmware that is causing an empty audio channel to mimic the other channel with the noise. The only next step is for someone else with a canon R7 or other model canon camera to see if this is consistant across their camera line, if its specific to the R7, or the remote chance that there is something special about my camera. Again, the tascam hotshoe adapter had the same issues while recording which eliminates the built in audio circuit of the camera also pointing to a flaw in the firmware.
Based on some research, I do not see a way to defeat an unused audio channel when using (internal, external or a Tascam accessory). Everything in the manual refers to stereo and the manual states on page 370 that volume cannot be adjusted between L/R channels. I understand what you are describing. The camera specs state compatibility with stereo mics, not mono (single channel). I don't feel the inability to defeat a single channel in a stereo (designed) intended application is neccessarily a flaw in the FW, but it might qualify as a feature request for some. Use the +product feedback option.
The R5 C just recently got a FW update that allows you to disable the internal mic when using an external mic or tascam accessory. For one channel however, post appears to be your only option.
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