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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Hiss

Z

zak forrest

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Hiss that I can't get rid of. I have a Sennheiser 416 plugged in with phantom power selected, no matter what gain settings i use the hiss is there. It's not the fan, and its not the LCD by the way.
 
zak, been hoping someone would post some audio clips. The only one I've heard so far is the quickie Evin Grant put up, and I noted in that thread that there was a disturbing amount of hissy noise in the recording (which had not been compressed). But his was admitedly not a very careful audio test, so I've been hoping there was an explanation like very low gain setting or mic setup.

Could you post a sample of what you're getting (just audio), each with details about the gain settings?
 
eclaire said:
zak, been hoping someone would post some audio clips. The only one I've heard so far is the quickie Evin Grant put up, and I noted in that thread that there was a disturbing amount of hissy noise in the recording (which had not been compressed). But his was admitedly not a very careful audio test, so I've been hoping there was an explanation like very low gain setting or mic setup.

Could you post a sample of what you're getting (just audio), each with details about the gain settings?
Click to expand...

http://zakforrest.com/red/audio


sennheiser 416 mounted on cam (its not fan or lcd noise though). dont remember the gain settings but they were pretty good. the hiss is there no matter what the gain...

you can hear the hiss nice and clean on the left, i think there is no audio on the left and only hiss.. on the right is some electric guitar and hiss..

ALSO- have only tried one pair of headphones so far, but my LEFT headphone is playing the RIGHT channel.. when i mute the left channel in the settings i dont hear anything in my right ear, etc... is this a bug with the red cam audio settings, or my headphones being mislabeled
 
I suggest you need to conduct some tests.

Go plug in a few other mics and see if the hiss continues. This will determine if your mic is somehow faulty.

Check these mics in another system (dosen't need to be a camera) and check for hiss. Your mic will continue to be noisy in any system if it's at fault. This should determine that the mics are good. If they are good then the camera settings, camera output, or internal system isn't functioning correctly.

Check your audio output for hiss. Some output amps, i.e., headphones amps can be noisy. Make sure your speakers, headphones are clean and not a source of trouble. Cords often cause problems caused by poor connections, RF, shielding, and other mysteries.

Bottom line, you need to do a bunch of various tests to isolate where the hiss is coming from.

If others are not having this problem, it could be your mic, cords, settings...
 
ive also tried my audio technica at 2020 and the problem is identical. in that sound clip i posted, you can hear th ehiss in the channel that the mike wasnt going into. it seems like any channel thats activated gets a hiss. its not the headphone outs cuz its hissing on my computer when i play a proxy...
 
The hiss I hear in your sample is very similar to what I recall from Evin's clip.

Nice to hear this is being addressed in a firmware update. Digitalfx, did you get that info from a private communication with someone at RED? I don't recall reading anything here regarding this issue.
 
eclaire said:
The hiss I hear in your sample is very similar to what I recall from Evin's clip.

Nice to hear this is being addressed in a firmware update. Digitalfx, did you get that info from a private communication with someone at RED? I don't recall reading anything here regarding this issue.
Click to expand...

I emailed support when I noticed the issue and they immediately responded.
 
Can you confirm that only one mic channel was open when you did this, that this isn't the sum of all 4 inputs all open @ mic level? Could you try recording nothing--nothing plugged in at all and see how hissy that is? Do you have a mixer you could plug in, take the camera down to line level and record that way? Thanks for the posting. This noise is another reason that I'd like to know what the Red's real phantom voltage is.

Philip Perkins CAS
 
Hiss (on some cameras)

Hiss (on some cameras)

I emailed support when I noticed the issue and they immediately responded.
Click to expand...

Yes, we are aware of it and working on it.... I think we have all the data we need for now.
 
zak forrest said:
no. ive phantom powered it for a long time now with all sorts of things..
Click to expand...

I ask because I had a strange hissy problem with a T-power (with converter) 416 on a Sony V1P a couple months ago... Good to know it's a resolvable problem!
 
Look for frame rate in hiss?

Look for frame rate in hiss?

Try making a WAV file of the hiss and bost the gain, then look for any periodicity in the wave form that is close to the frame rate the camera is running at. It is hard to filter all the digital noise out of the power and bias in the audio circuits to get 120db S/N. The circuit baords can have capacitive and inductive coupling, that goes for the mic cables as well since the power drain is in the AMPS going into the camera... you would not want the mic cable near the monitor and such (the backlight makes a 20KHz magnetic field)...

If the hiss is not linked to the frame rate (shoot a frame that is top half white and bottom half black then left white and right black) it may be from the voltage regulator feeding the audio section since there can be issues with noise in the power. Or they may just need to add a stage of desecreate JFET with the bias set to high current to lower the Z on the source lead. Also if the input capacitor is too small it can give low Hz noise, to fix that use 10mf or more on the input, even if the JFET input is in the Meg ohm.

Try making a mic input plug with a 600 ohm metal film to see what the base noise is, shorting may give a false level...
 
I wonder if this could be partially the quality of the preamps. Sound Devices makes excellent preamps.
 
Will external preamp help?

Will external preamp help?

If the problem is just some noise in the preamps, and they have enough head room then using a good external pre-amp to get the signal 40db or more higher should help. But if the internal preamps or A2D's are making noise and the noise does not fall when the gain is turned down in the camera, then you cannot "yell" over all the hiss...

I have build low noise preamps, when you get the noise very low and you flex the mic cables you can hear a "tinkling" sound like small bells, normally the pre-amp hiss is way over that.

It may be best anyway to have a external preamp within 3 feet of the mic, and run a stronger signal on the long cable to the camera since the camera will be making EMF and RFI with all of its power and other cables going to the monitor and memory packs...

With double system sound the audio is far from the camera and its EMF/RFI...
 
Hmm...not just white noise (on the silent channel), it does seem to be modulated by the capture rate.
The Aiff posted was sample rate converted into 44.100, and a rough mesurement of the modulation lenght was 1850 samples, so thats very close to 24p.

redmodul.jpg


There is also some crosstalk audible across the channels, dont know how much this signal is boosted through the chain though. Eliminating it totally is close to impossible in a portable device.
 
Change to Digital input for audio?

Change to Digital input for audio?

If they put the audio external in a solid block of metal with MU metal shields, and have a digital input for the Audio that should help get the noise down to studio levels.

I built a digital bias oscillator once for recording on Mag film, and had a divide down to get 1000Hz output. When it was used there was a 1000Hz whine in the audio from small -100db+ load on the power supply, so I unpluged the divide down chips and the whine went away.

It is probably a fixable problem, but it is never good to have anything digital close to analog since even a few pf can cause crosstalk...

Great illustration! I see that all the time, I live in the direct beem of a TV xmiter so I can tell 60Hz from TV by the fact that if I sync my 'Scope to the power line Hz the TV ripple moves slowly like a worm....

P.S. That is a great way to check the camera frame rate! Just count the distance between 100 ripples, but it will be off a little since computer sound boards are off about one frame per four minutes of recording...
 
Anders Holck said:
Hmm...not just white noise (on the silent channel), it does seem to be modulated by the capture rate.
The Aiff posted was sample rate converted into 44.100, and a rough mesurement of the modulation lenght was 1850 samples, so thats very close to 24p.

redmodul.jpg


There is also some crosstalk audible across the channels, dont know how much this signal is boosted through the chain though. Eliminating it totally is close to impossible in a portable device.
Click to expand...

Great find, Anders. Always the analyst :-)
 
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