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Old June 20th, 2019, 09:06 AM   #1
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Headphone audio

Many times when I film a dance recital or theater performance and need a board feed I have to as a last resort plug into the sound board’s headphone jack. I would rather have a mono feed from aux xlr out often a teenager who’s only there to operate it has no knowledge to give me a proper feed or sometimes the board doesn’t have enough outs and yes I always request a feed in advance but inevitably you get there and you are struggling to get audio.

So the question is, is there anything wrong getting audio from the headphone jack? The other question is what’s the best 1/4 to xlr adapter (mono vs stereo) and how it effects the feed. I’ve had some board operators tell me only use a stereo 1/4 as opposed to a mono. I assume no matter what adapter ( stereo or mono 1/4 to xlr) into a headphone jack isn’t going to sum a stereo feed but rather discard one of the channels? This will travel through an xlr cable into one of the camera’s channels.
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Old June 20th, 2019, 10:22 AM   #2
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Re: Headphone audio

Option 1: For mic level XLR input. Purchase a DI (Direct input) box (for instance the low cost Rolls DB-25(b) has two 1/4" inputs and a single XLR mic level out. it also has switchable or variable attenuation) There are other DIs available that have RCA and/or 1/8" inputs.. You may need a standard off-the-shelf adapter cable though for a 1/4" headphone output.

Option 2: For line level input. Build or have someone build a custom 1/4" TRS to XLR cable/adapter. Wired as such: 1/8 or 1/4 inch TRS, Tip and Ring connected to XLR pin-2, Shield/ ground to XLR pins-1 and 3.
BE AWARE: a standard off-the-shelf 1/4" TRS to XLR adapter would result in no audio at all... the Left/Right <> Hot /Cold configuration would be 180 degrees out-of-phase on a XLR input .
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Old June 20th, 2019, 10:42 AM   #3
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Re: Headphone audio

You could us a passive line mixer (e.g. Behringer Micromix MX400) to combine the stereo output of the headphone jack to mono. Use a TRS to dual TS "insert" cable to connect them.
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Old June 20th, 2019, 10:45 AM   #4
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Re: Headphone audio

Quote:
Originally Posted by Rick Reineke View Post
Option 1: For mic level XLR input. Purchase a DI (Direct input) box (for instance the low cost Rolls DB-25(b) has two 1/4" inputs and a single XLR mic level out..
Except then you're connecting two amplifier outputs together without isolation. I would not recommend this. The two 1/4" jacks are not two inputs, they are parallel so you can patch through the device using one as an input and one as an output.
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Old June 20th, 2019, 11:03 AM   #5
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Re: Headphone audio

There are several caveats to this method. Not to say that I haven't resorted to using it myself on occasion.

Using the headphone output means that the operator can't use the headphones (as for cue, preview, etc.) and is subject to the operator leaving the controls fixed (which bus is monitored, headphone level, etc.). That is rather dodgy IME and only an option low on my list.

Taking only one channel (Left or Right) and discarding the other is OK if they are running the system completely in monaural. But, of course if they are playing the tracks in stereo, then you are getting only 1/2 the music and likely to sound strange.

I love the Rolls DB25 iso box. I have several of them myself and always keep at least 2 or 3 in my remote kit. But @Patrick Tracy is correct that the two 1/4 inch TS jacks are connected in parallel to allow "looping". Connecting the Left and Right output from anything hard-wired together is rather an abuse and frowned upon. Although it is unlikely to actually damage the gear and only somewhat likely to damage the audio signal either. I admit to violating this rule on more than one occasion. But it is not "proper".

But the iso box is a great tool to isolate you from the venue system (with the transformer), and trim the level to something comfortable to your gear, AND to convert to balanced, low-impedance so that you can run the signal a long distance where necessary. I highly recommend the Rolls DB25

And note carefully @Rick Reineke's caution about taking unbalanced stereo (as a headphone output) and connecting it into a balanced input. Many people have come through these forums asking how to fix their audio tracks that have Left-minus-Right problems.
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Old June 20th, 2019, 10:26 PM   #6
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Re: Headphone audio

Forgive me for asking what is surely an amatuer question, but at a dance recital, presumably the music is pre-recorded. Can you not grab a copy of the original MP3 file, or rip the CD's to a latop, and then synch/mix them in post?
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Old June 20th, 2019, 10:46 PM   #7
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Re: Headphone audio

I use one of these: AV Direct – Audio/Video Direct Box – ART Pro Audio

or one of these for stereo: http://artproaudio.com/product/dual-rdb/
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Old June 21st, 2019, 03:02 AM   #8
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Re: Headphone audio

Quote:
Originally Posted by Vince Pachiano View Post
Forgive me for asking what is surely an amatuer question, but at a dance recital, presumably the music is pre-recorded. Can you not grab a copy of the original MP3 file, or rip the CD's to a latop, and then synch/mix them in post?
I don't know about MP3 files, but CDs do drift, so depending on the action you can find sync drifting. This was an issue when shooting music videos to CD playback, so the editor had to make sync adjustments when cutting to the music track.
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Old June 21st, 2019, 05:44 AM   #9
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Re: Headphone audio

I've never had any Digital source drift once we moved to decent PLL control - mp3, CD, any of the data formats are stable enough for normal sync purposes. Pinching the CDs is a good move - always a good fix!
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Old June 21st, 2019, 06:19 AM   #10
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Re: Headphone audio

Quote:
Originally Posted by Vince Pachiano View Post
Forgive me for asking what is surely an amatuer question, but at a dance recital, presumably the music is pre-recorded. Can you not grab a copy of the original MP3 file, or rip the CD's to a latop, and then synch/mix them in post?
It’s possible but very time consuming. First you have to convince the director to mail them to you. Most of the time the songs have been customized for content and length. There can be real time issues like in my last recital the cd skipped in a couple of places like wise it can also skip while ripping. That’s very hard to sync because you can’t remove the skip. Sometimes they will restart a song if there is a dancer problem. In addition I’ve found syncing software has difficulty with classical and with ambient that has reverb. Syncing 50 individual songs just isn’t fun. While there would be drift between what the camera recorded and the actual music since the songs aren’t played continuously there wouldn’t be enough time for them to drift enough to hear.

Last edited by Pete Cofrancesco; June 21st, 2019 at 09:09 AM.
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Old June 21st, 2019, 06:47 AM   #11
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Re: Headphone audio

Back to my initial question, plugging a 1/4 to xlr adapter into the board’s headphone jack.
1. What would happens to the channels if you plug a mono adapter into a stereo jack?
2. What happens when you plug a stereo adapter. Because I assume that the left or right channel will be sent through the pin/wire that is reserved for reversed polarity to make it balanced. So what does the camera do since it’s expecting a balanced mono feed but instead is receiving an an unbalanced stereo feed?

I get that because the distance is so small that there are no noise issues sending unbalanced signals.
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Old June 21st, 2019, 08:43 AM   #12
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Re: Headphone audio

Quote:
Originally Posted by Pete Cofrancesco View Post
Back to my initial question, plugging a 1/4 to xlr adapter into the board’s headphone jack.
1. What would happens to the channels if you plug a mono adapter into a stereo jack?
You get the Left channel, and the Right channel is shorted to ground. Shorting the output of a piece of modern gear is unlikely to damage it as most modern gear is designed to be "short-circuit-proof".

Quote:
2. What happens when you plug a stereo adapter. Because I assume that the left or right channel will be sent through the pin/wire that is reserved for reversed polarity to make it balanced. So what does the camera do since it’s expecting a balanced mono feed but instead is receiving an an unbalanced stereo feed?
Depends on what you mean by "stereo adapter"?
If you mean something that combines Tip (Left) and Ring (Right) signals together then you should get a proper mix of stereo down to monaural.
But if you mean something that connects Tip to XLR pin 3 and Ring to XLR pin 2, then you will record Left-minus-Right which will typically be horrible and unusable.

Quote:
I get that because the distance is so small that there are no noise issues sending unbalanced signals.
Distance is only ONE (and perhaps minor) issue. A much larger issue is ISOLATION between the venue system and your gear. Of course, if you are only operating on batteries, you can probably get away with it. That is why I like the Rolls DB25 iso boxes. So that the interconnection causes no problems for either me or for the venue system.
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Old June 21st, 2019, 09:16 AM   #13
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Re: Headphone audio

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Originally Posted by Patrick Tracy View Post
Except then you're connecting two amplifier outputs together without isolation. I would not recommend this.
I would not 'recommend' using a HP output in the first place. It is basically a functional work-a-round when no other options exist. Tying L/R HP terminals together will not damage anything.. in most cases.
PA system power amps are another story.
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Old June 21st, 2019, 09:25 AM   #14
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Re: Headphone audio

Quote:
Originally Posted by Pete Cofrancesco View Post
...I get that because the distance is so small that there are no noise issues sending unbalanced signals.
With a direct-box (DI) method you should be getting mic-level balanced on XLR connectors to your camera. With XLR inputs on your camera, you should be good for up to 300 feet (100 meters) using decent cable.

I myself haven’t used the Rolls DI, but, do look for one with a switchable pad, and take time to set it during rehearsals or sound check. This may be an instrument/amp switch, or, could be a sliding switch with 0, -20db, -40db positions. In theory, a headphone output is close to line-level. In practice it varies widely.

My usual DI is an EWI FB-202 2-ch, which can solve some problems. You can always use just one ch. A specific adaptor cable in 1/4” that takes one stereo to two mono signals is readily available, like a Hosa STP-201 from your favorite retailer or online source.
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Old June 21st, 2019, 09:40 AM   #15
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Re: Headphone audio

FWIW, the original (discontinued) Rolls DB-25 had a switchable 20, 40 dB pad. The updated DB-25b has a variable pad pot. Both have a ground lift switch and are passive (does not require battery or Phantom power).
There are others like the aforementioned ART worth looking into as well,,,, specially made for HP outputs on computers and such.
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