CP750 Robosound

[Steve Guttag]

Has anyone found a "failure mode" in the CP750 manifest itself as "Robosound?" It will play one show fine but on the next show, it will be back to robosound. This tells me that there may be a clocking issue. Rebooting things clears it up, for a show.

[John Thomas]

Plenty of known failure modes on 750's but never seen that one. What's the server? Certain DCP's will do weird things on certain servers too. I've had an ICMP update solve a robosound type issue before, for example.

Any indication about certain channels being robosound and others being fine?

I have seen one that was stuck acting like it was getting clock on digital 2 with nothing plugged in, not sure if that actually affected the audio though.

[Steve Guttag]

Dolby DSS200/CAT745...a rather aged installation.

[Harold Hallikainen]

It's been a while, but I think I recall the robosound issue on the CP650. I THINK it has to do with the clock phase on the AES3 inputs not being precisely aligned between channels. As I recall on the 650, I think the whole system clocks off the first pair and if the other pairs are not aligned right, you get some pretty strange sound. USL did make a box to correct that (multichannel sample rate converter to locate at the CP650 with all in sync). I don't know if the CP750 is similar, but as I recall looking inside one, there are not AKM SRC chips, so the DIR is in an FPGA and may or may not have sample rate conversion. Is the OMB to CP750 wiring CAT5 or similar? Are both cables identical length? Is this 5.1 or 7.1? The CP750 has an interesting way of getting 7.1, and I don't know if it relies on the clock from one pair for all the other pairs.

Not much help, I know!

Good luck!

Harold

[Steve Guttag]

Yeah, the CP650 robosound is well-known. Honestly, I believe the cable is a GDC AES cable from the original box server and then there is an adapter RJ45 to HD26 adapter cable.

[Marcel Birgelen]

Never have seen or rather heard this happen on a CP750, but those things are now getting into the years that we may see some odd failure behaviors.

I'm pretty sure the clock source for the 4xAES is the first pair, so if it's an AES clocking issue, you should be able to detect that by pulling the plug on all channels but Front Left. If that one still sound "good", but the others don't, then your AES signals are most certainly out-of-sync. In that case, the problem is most likely on your server and not on the CP750.

[Carsten Kurz]

Maybe it is not a CP750, but CAT745 or cable issue. I never heard about Robosound with the CP750 on any forum or among colleagues.

[Leo Enticknap]

How difficult would it be to hook that IMB to another CP750 to see if the problem remains? If it's a gallery booth with multiple screens, all you'd need is a couple of long patch cables. But if it's a single screen arthouse, forget it, I guess.

[Steve Guttag]

Someone I know has claimed to have experienced the problem on the CP750...problem was the power supply. We'll see.

[Marcel Birgelen]

If that works out to be true, the CP750 power supply failure has gained my respect for the sheer amount of possible failure modes.

[Dave Macaulay]

The PSU failing can do some really weird things. Some are resolved with a new PSU, some cause permanent damage. I haven't had "robosound" but have had distortion, very loud screeching in all channels, locked controls, lost automation.
Usually the PSU gets considerably hotter than normal. One of the +/-15 DC rails tends to go high which gives the weird symptoms, losing one gives super distortion. Losing 5V will just shut it off.
Racking a CP750 tight between components that block the PSU cooling holes is going to really shorten its life, minimum1U open above and below is needed.
Dolby says they will continue providing PSUs for a while, but other parts are NLA and "existing orders will be cancelled"... so if you're expecting motherboards, don't.

[Marin Zorica]

Another interesting stuff about CP750. They started the show cue sent from server was fader level 4, digital input 1, unmute......only low sound in room like the fader was 0.5. Operator tried everything like mute/unmute, change inputs, level etc.....still the same. Than he reboot complete system (power off from mains) including server, processor, projector and stil the same....after about minute sound came in and works without problem since last few days. I did check in log of cp750 and relly he did everything he described. This is most weird CP750 behaviour i have ever hear of. I doubt problem was aes from server since sound was there but ver, very low, also if it was amp, some channel would work.

[Carsten Kurz]

I have seen low output level with bad power supply, but especially with overheating units.