Mike_Feldman

Mike_Feldman

Lives in United States Champaign, IL, United States
Works as a Retired
Joined on Apr 26, 2018
About me:

Waging hobbies: photography, videography, broadcast audio, guitar, cooking.

Comments

Total: 9, showing: 1 – 9

I've mentioned the problems that I've experienced with the 2.5 volt DC Plug-in-Power that Sony a7 cameras' mic input jack presents to the audio input source. I took the time to make a very quick and dirty video with my a7Sii to demonstrate the issue, and I thought I'd share it here. Note that the video is comprised of 5 clips and that I did no audio filtering, so what you hear is what the camera recorded. And, indeed my DC blocking circuit seems to have one channel shorted out ... probably a solder blob ring to sleeve.

http://feldman.gidnoy.com/movies/20200409_Mike_Feldman-Sony_a7Sii_Plug-in-Power.MP4

Link | Posted on Apr 9, 2020 at 07:25 UTC as 14th comment
In reply to:

Antisthenes: DPReview should measure the DC voltage present between the tip and the sleeve of ALL the cameras involved in this preamp test.

My bet is that ONLY the Sony provides Plug-in-Power (PiP) to the mic, and will therefore have a DC voltage present. This should clearly show why the Sony is different from all the other cameras.

ANY TEST SETUP THAT DOESN'T TAKE INTO ACCOUNT THE PRESENCE OF THAT DC VOLTAGE, INJECTED BY THE CAMERA TO POWER A MICROPHONE, IS ELECTRICALLY INCORRECT, AND INVALID.

A mic's output stage can use a negative feedback (NFB) amplifier to drive its load — i.e. the possibly quite long signal line and the input impedance of the recording device.

https://en.wikipedia.org/wiki/Negative-feedback_amplifier

../..

Thank you for spelling this out out in such great detail. I suspect that it will prove enlightening for those sound technicians here calling themselves sound engineers.

Which is why I wish Sony had provided a way to defeat PIP in their cameras with microphone input jacks.

Link | Posted on Apr 7, 2020 at 03:11 UTC
In reply to:

Ed Ingold: The Rode Videomic has a built-in amplifier with a line level output, adjustable from -10 to +20 dB. Most outboard microphones for use with hybrid cameras are similar. The Sony A7iii has a microphone level input with unspecified sensitivity. It also has a 7.2 VDC power supply which may not be compatible with some inputs.

In order to keep from clipping, the audio gain in the camera must be set. For a hot input like the Videomic, this is probably at the minimum level. At the same time, the powered mic output must be set to its lowest level.

Ed, the 7.2 volts that you mention is the Sony battery voltage; it also takes 5v from USB.

I've seen a few contradictory values for the Plug-in-Power bias voltage at the mic input jack. I just measured my Sony a7Sii's mic jack, and it's 2.55v + on tip and ring, with respect to sleeve.

Link | Posted on Apr 6, 2020 at 05:29 UTC
In reply to:

Raynaud: It looks like there is a real problem with the Sony the reviewer found.
It deserves and asterisk if ranked higher. Many of us already have microphones and do not wish to shop and test new ones to find one that works.
maybe one you have will work very well, but maybe you get the awful his and need to buy another microphone.

I've had problems before now. But when finding a way to feed from line-level external audio. If my project requires pristine sound, then I use an external recorder. But it's way easier in post if the audio tracks in the video file are good enough.

Link | Posted on Apr 4, 2020 at 18:45 UTC
In reply to:

whawha: As a studio owner and sound engineer myself, I would be interested in knowing exactly what was causing the Sony camera to perform badly with certain mics. If the preamp in the A7III is well designed, ie supplies adequate power has generous gain and s/n ratio (and I think that it most probably is), there could be some differences in tonality when trying different microphones but not such drastic differences in performance. Even an (unlikely) impedance mismatch would not cause such behaviour. Why exactly were some microphones giving out noisy results and other weren’t?

I think that how the output of the driving device (microphone, wireless receiver, etc.) is coupled has a lot to do with it in the face of the 2.4v Plug-in-Power the Sony drives back into it. A transformer coupling or non-polarized capacitor coupling would probably work best, and an output transistor maybe not so good. The Zaxcom URX100 receiver's output jack doubles as it's headphone amp output.

Link | Posted on Apr 4, 2020 at 18:37 UTC
In reply to:

Antisthenes: I have serious reservations about the validity of such a preamp "test".

That youtube video shows close-ups of the 3.5mm microphone plugs of all the cameras tested. It appears that only the Sony has an /explicit/ mention, next to the plug, that the mic connector provides plug-in-power — i.e. it provides the electrical energy needed to power an electret condenser mic.

If a mic input doesn't provide power, then, the microphone must have its own power source — typically a battery.

Connecting a voltmeter to the "plug-in-power" mic input of a Sony still camera, I've verified that it provides a 2.4-volt DC bias between the sleeve and the signal lines.

In the youtube video, the tester seems to be connecting a wireless mic receiver unit to the cameras' mic input. Needless to say, a wireless receiver unit has its own batteries, and doesn't need to receive DC electrical power via the microphone cable connecting it to the camera.

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Also, take into consideration the gain-staging between the audio source and the cameras' mic input levels. -60dBU out into a high gain setting in the cameras might produce significantly different results from -40dBU into a low mic gain settings.

Link | Posted on Mar 31, 2020 at 19:44 UTC
In reply to:

Mike_Feldman: One thing that really annoys me about Sony Alpha's external microphone input, and you can see it proudly printed next to the jack, is Plug-In-Power. That's 3v DC to power the simple electret mics. There's no option in the camera to turn it off. In theory, you can't hear DC (zero Hertz), but in practice, DC is the worst thing you can to to a potentiometer (simple volume control on your feeding device), or the voice coil of a dynamic mic (slams it against the stops), or even a slightly corroded connector (crackles when you bump it). I wonder if the feeding devices in the test suffer from having DC across their output?

As far as the audio inputs on the Sony Alpha's hot shoe, there's no volume control for that input like there is for external mic jack. The $600 KLR K2M box has volume control but comes with a shotgun mic none of us want. ECM-XYST1M mic through the hot-shoe is too hot; volume control in the camera requires the 3.5mm patch cable (included) to mic in (crackle). -- Mike

I shoot a lot of loud bar bands video with a Sony a7Sii fed from an external mic/audio recorder setup and most of the time I'm happy with the video file's audio track. The only time I use the audio from the recorder is when the camera's audio is noisy from cable movement when panning, or when I botch the levels on the camera. I never notice noise on the camera's external mic feed when the camera and cables are still.

If the a7Sii's mic level is set way high, then it might start showing noise, but I usually run at a mic level of 5 out of 31 since I feed it pretty hot.

A interesting experiment would be compare noise levels with sequence of decreasing mic gains along with increasing feed levels. I've never used an a7iii, but I'm guessing you can get adequate signal to noise from the external mic input with proper gain staging.

Link | Posted on Mar 30, 2020 at 05:25 UTC
In reply to:

Mike_Feldman: One thing that really annoys me about Sony Alpha's external microphone input, and you can see it proudly printed next to the jack, is Plug-In-Power. That's 3v DC to power the simple electret mics. There's no option in the camera to turn it off. In theory, you can't hear DC (zero Hertz), but in practice, DC is the worst thing you can to to a potentiometer (simple volume control on your feeding device), or the voice coil of a dynamic mic (slams it against the stops), or even a slightly corroded connector (crackles when you bump it). I wonder if the feeding devices in the test suffer from having DC across their output?

As far as the audio inputs on the Sony Alpha's hot shoe, there's no volume control for that input like there is for external mic jack. The $600 KLR K2M box has volume control but comes with a shotgun mic none of us want. ECM-XYST1M mic through the hot-shoe is too hot; volume control in the camera requires the 3.5mm patch cable (included) to mic in (crackle). -- Mike

Boy, Ed, let's start with "speaker" ... nowhere in my post did I use that word. I wrote "dynamic mic". I see that you are an expert in misinformation, or at least misunderstanding. It's just that I don't like the *idea* of DC across the voice coil of a dynamic microphone, who's signal output is millivolts, and the DC is 3 volts.

I get my information from direct experience with my Sony a7Sii, which I regularly feed external stereo audio into the mic in from a Radial Pro-ISO DI, which has a volume pot on it's unbalanced stereo mic level output. Just touch the pot while recording, and the noise clips!

You also seem to be of the opinion the camera's mic in is balanced mono, but it's unbalanced stereo. And just touch the patch cable to the mic in while recording and you get noise.

I don't own an XLR-K?M (? == 1, 2, or 3). The only hot-shoe audio input device that I own is the ECM-XYST1M, which has no volume control. Trim pots, faders are cap coupled to block DC.

Link | Posted on Mar 30, 2020 at 02:04 UTC

One thing that really annoys me about Sony Alpha's external microphone input, and you can see it proudly printed next to the jack, is Plug-In-Power. That's 3v DC to power the simple electret mics. There's no option in the camera to turn it off. In theory, you can't hear DC (zero Hertz), but in practice, DC is the worst thing you can to to a potentiometer (simple volume control on your feeding device), or the voice coil of a dynamic mic (slams it against the stops), or even a slightly corroded connector (crackles when you bump it). I wonder if the feeding devices in the test suffer from having DC across their output?

As far as the audio inputs on the Sony Alpha's hot shoe, there's no volume control for that input like there is for external mic jack. The $600 KLR K2M box has volume control but comes with a shotgun mic none of us want. ECM-XYST1M mic through the hot-shoe is too hot; volume control in the camera requires the 3.5mm patch cable (included) to mic in (crackle). -- Mike

Link | Posted on Mar 28, 2020 at 20:14 UTC as 53rd comment | 3 replies
Total: 9, showing: 1 – 9