Film-Tech Forum ARCHIVE: CP750 H/I Output / Aux Output 7

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Posted by Max Hayman (Member # 8726) on 04-15-2016, 12:17 PM:

Hey,

We have just had a hearing loop installed and have been having some trouble getting the Hearing Impaired audio from our CP750 (Channels 7/8 redirected to Digital 2). I can get the Audio Description out from the Aux Channel 8 (some DCPs its on 7 aswell). Apparently Channel 7 should contain the HI information, and if its not there you should use the H/I output which takes a centre weighted sum of LCR.

However I don't think I have found a DCP yet which has the HI information on Channel 7. It also seems like our H/I Out RCA port isn't actually giving out any audio.

Has anyone had this issue.

Posted by Marco Giustini (Member # 4544) on 04-15-2016, 06:30 PM:

That's correct, use the HI output which has also the advantage of making HOH out of everything, including commercials and trailers.

HOH is currently not included on DCP's. But for the aforementioned reason I wouldn't use it anyway. Just trust your CP [Smile]

Posted by Carsten Kurz (Member # 5396) on 04-16-2016, 05:08 AM:

Max - I suggest you make your own Test DCP for HI and VI, so in the future you can sort out things like this quickly.

Doing this with DCP-o-matic is easy.

- Carsten

Posted by Marco Giustini (Member # 4544) on 04-16-2016, 08:15 AM:

I missed the HI output not giving any audio. I am not aware of a way to disable it, it should work all the time. If you do not have any output, then your 750 may be defective.

Posted by Max Hayman (Member # 8726) on 04-16-2016, 08:35 AM:

Right. Worrying that our CP750 may be defective, couldn't find anything in the manual which would explain it not working either. Currently I can just route the Centre channel to the hearing loop which might be a temporary solution.

Posted by Carsten Kurz (Member # 5396) on 04-16-2016, 10:19 AM:

Software version, 5.1/7.1 config? Do you have a current manual? Certain operating modes of the CP750 influence the channel routing for 7.1 and HI/VI, you need to get this very clear.

- Carsten

Posted by Marco Giustini (Member # 4544) on 04-16-2016, 11:45 AM:

Carsten,

The HI (not channel 7) RCA output should output sound all the time - not sure about non-sync sources but I believe so.

Channel 7 AUX out can be affected by configuration indeed.

Posted by Gavin Lewarne (Member # 5397) on 04-17-2016, 05:25 AM:

Our CP750 has quite a low output level on the HI, and without running it through a carefully adjusted preamp to boost it a bit, it doesn't always turn on our Senheiser IR hearing thingy (which only activates when it gets a relatively high input level)

Posted by Max Hayman (Member # 8726) on 04-17-2016, 06:14 AM:

Thanks guys. I will be in tomorrow to check which version and configs we are using, just incase that affects anything. I doubt we are using an up-to-date version. I am guessing you need to be approved to the Dolby site to be able to see the downloads, correct?

Thats good to know Gavin, I will try hooking up some more sentitive hardware to it and let you know the results.

Posted by Marco Giustini (Member # 4544) on 04-17-2016, 12:11 PM:

I'm not aware of any changes to the HI output with newer versions but last is 1.2.8.3 and hasn't been updated for years

Posted by Max Hayman (Member # 8726) on 04-20-2016, 08:19 AM:

Does the volume of the H/I work with the volume control? As we usually run films on 4-5 instead of 7. Perhaps this could cause something?

Posted by Tony Bandiera Jr (Member # 2365) on 04-20-2016, 10:36 AM:

quote: Max Hayman
Does the volume of the H/I work with the volume control? As we usually run films on 4-5 instead of 7. Perhaps this could cause something?

IIRC it does track with the fader...do a quick test, turn the fader to "7" and see if the HI output goes up.

Posted by Pete Naples (Member # 761) on 04-20-2016, 01:56 PM:

I believe it does indeed follow the fader, because it's a mix of L, C & R with C a wee bit hotter. +6dB rings a bell.

If the HI output is low at your normal fader setting you could use a pre-amp, I tend to use one of these. It lets me mix multiple sources and route them to different HI/VI transmitters whislt keeping all the levels even.
Ultra Link

For simpler systems with only induction loop or single channel IR and no VI, it's worth checking how the whole sound system is gain staged. If it's been done less than optimally (all the power amps set at max gain), the HI output from the processor, being a function of the main output, will be low. Dropping the power amps gain and running the CP750 outputs hotter will address that, as well as give the other benefits associated with good gain staging.

Posted by Harold Hallikainen (Member # 5405) on 04-20-2016, 02:04 PM:

I'd be surprised if the HI output followed the main fader. It definitely does not in USL processors. In USL systems, HI and VI both output 300mV RMS when presented with -20 dBFS.

A general thing on troubleshooting (from my days in radio) is to have something to actually listen to an analog line. This can be a pair of headphones, or a cheap amplified speaker (Radio Shack has these). It's really nice to know whether the problem is your HI transmitter itself or the fact that it's not getting audio. I had a call this morning where the tech said there was no VI audio. This was with a CP750. He could not tell me if the auditorium was wired for 5.1 or 7.1, which certainly affects how things are wired on the CP750. Finally, we determined that the content had no VI track. I have not heard back, so maybe that was the problem.

For test content, have a look at http://ftp.uslinc.com/ftp/TestContent/index.htm . Sintel is a short movie. WGBH added closed captions and audio description. Fox packaged it for ISDCF. I think every tech should carry this around on a flash drive.

Harold

Posted by Pete Naples (Member # 761) on 04-20-2016, 02:08 PM:

That's a very handy DCP Harold!

Posted by Steve Guttag (Member # 268) on 04-21-2016, 06:40 AM:

Harold,

Historically, Dolby processors always had HI track the fader (if it was recorded too loud for everyone, then it would probably hit the transmitter too hard too and possibly clip it since that level would be set by someone listening to an average level.

I don't recall verifying that this is the case with the CP750 but it was definitely the case through the CP650.