MixPre with Tentacle Sync Issues

I expect this thread will be almost empty as my MixPre-6 II with Tentacles reliably perform so well together. After years of flawless results, I experienced my first anomaly last weekend.

On the MixPre, media files have that mysterious maximum size limit after which the large file is closed and the recording automagically opens another file to continue recording in very long takes. There’s no gap on the timeline, no loss of audio data or timecode between the two files of a single take.

This happens to me frequently since my shoots can be over 120 minutes with one intermission. However in the fashion shoot I was told to prepare for a two hour shoot without any intermission. It was non-stop models interspersed with choral singing without a minute pause. No problem… I thought.

When I loaded the MixPre files on the timeline, I was shocked. The end of the first file had some weirdness on the timeline and there was a gap of several seconds before the audio reappeared in the second file. The shock was the timecode on the continuous video take no longer matched the timecode on the second audio file. All the audio was there but shifted to the right on the timeline. I used the scratch audio from the BMPCC4K and was able to manually get everything in sync.

I had a single Tentacle that first jammed the MixPre and then mounted the Tentacle on the camera for the duration. I could have left a Tentacle on the MixPre but it wasn’t ever necessary as the MixPre does a superb job maintaining sync once it’s jammed.

Don’t know why this happened and grateful no audio was lost, but so weird. I’m going to test this before my next major shoot in two weeks.

I don’t know if the SSD was a factor but I’ll experiment with both the Wise 1TB and the Samsung T7 Shield 2TB to see if both cleanly make the switch when exceeding the single file capacity. I could have used the CFast cards but the camera used only SSD. I think I should also test this with the CFast2 cards as well. The MixPre uses a proprietary 32GB SDXC, but I hope that’s not the issue, so I could test using my Wise 128GB SDXC which I’ve used before successfully. Going to be a full day or two of testing, but the next shoot must be flawless.

Anyone have any insights on this rare event?

The file size limit comes from the file system. IIRC it's either FAT or ExFAT, both of which are 32-bit file systems, which therefore limit the file size to 4GB -- because that's as much as a 32-bit address can... address.

My guess regarding the delay is also file system related; when writing to a single file the recorder is streaming data continuously to the recording media, and with an internal SD there's no latency to open a new file. But on the external SSD there apparently is, in order to allocate the starting file blocks and probably also to update the disks table of contents.

That latency might be a result of going through USB-C, since that's an external interface that adds its own latency.

It might be worth asking the folks at Sound Devices; they'd probably have more insight due to actually knowing how their file system is implemented rather than guessing like I am

Also I wonder if Sound Devices has updated its file system in the MixPre series. I haven't checked in a while.

I should look into it on the Sound Devices website. I usually keep up with their software updates but probably a good idea to update if there’s a newer version. I’m using their proprietary 32GB SDXC card and usually format the card via the MixPre so it should be kosher. I will have about ten days before my major shoot so time to test and see. So odd that I’ve had a file split several times and never missed a frame let alone miss writing for several seconds.

Amazing the MixPre never lost any actual audio data during this weirdness but the data was written with an inappropriate timecode. I think timecode is written just at the moment the audio data is written rather than timecode being kept with the audio in its buffer. The buffer worked great though and is more important than timecode since I manually adjusted in post.

Hi Rick

I hope that this is a one off event ... potentially an ongoing concern ...

I assume that there will be drift at 2 hours ... minor but still a concern.

I record with a 633 hard synced to my Komodo X ... but still use a physical
clap to ensure that things stay a bit aligned.

My USBPre2 is running as a streaming audio endpoint after a lightning stike
killed a major number of video, audio, internet, alarm, garage door openers, and
most of the power supplies to devices in the house ...

Stuck the roof ... which was a month old ... and protected us from a devastating
burn to the ground event which occurred in our town the day before.

I always synced with Ambient so do not know if it is inherent in the Tentacle and they
need an update.

The ExFat limitation is of concern ... however my Komodo X splits at 4gb ... and the TC sync has
been perfect ... but no Tentacle or Ambient ... just hard wire to the 633.

Can you get the MixPre close enough to your camera to do a direct connection?

Unless the MixPre is failing I imagine that the less rigorous wireless connection may be
the culprit.

Forgive the riff above just thinking about inherent liabilities and weaknesses ...

Bob

Hi Rick

I hope that this is a one off event ... potentially an ongoing concern ...

My USBPre2 is running as a streaming audio endpoint after a lightning stike
killed a major number of video, audio, internet, alarm, garage door openers, and most of the power supplies to devices in the house ...

Struck the roof ... which was a month old ... and protected us from a devastating
burn to the ground event which occurred in our town the day before.

Can you get the MixPre close enough to your camera to do a direct connection?
…

Yes, I can do that if needed. If recreating the problem happens during testing, I can go that route.

Glad your home was safe after that lightning strike!

Thanks, Bob.

exFAT does not have the 4GB file size limit. It's akin to NTFS, but less Windows-centric.

Field recorders do not need to break up long recordings. It's very frustrating that they do.

exFAT does not have the 4GB file size… Field recorders do not need to break up long recordings. It's very frustrating that they do.

Absolutely wonder what century Sound Devices thinks they’re in.

You know I think I’ll just go with my own Wise 128GB SDXC card for the major shoot coming up soon and put an end to the drama. I have successfully tested using my own card in the past. I’ll do that and test for several hours with three XLR mics like the fashion show.

Although it was a freak occurrence that the split file had a one-time anomaly, that could escalate to be a disaster.

Thanks for the kick in the pants, Jim.

exFAT does not have the 4GB file size limit. It's akin to NTFS, but less Windows-centric.

Field recorders do not need to break up long recordings. It's very frustrating that they do.

Jim, I checked the SDXC card in the MixPre and it’s ExFAT but the largest single file the MixPre will write is always 4.29GB.

So this is some archaic internal software limitation in the MixPre firmware. I am running on version 9.02 which is the latest version released July 18, 2024. I have emailed Sound Devices.

exFAT does not have the 4GB file size limit. It's akin to NTFS, but less Windows-centric.

Thanks for that correction. It's been so long that I forgot that it had more than 4GB file support. I was thinking of Fat32. But I was correct about the MixPre-D using exFAT, ironically

Field recorders do not need to break up long recordings. It's very frustrating that they do.

I wonder why they haven't updated their file writing code to eliminate that limitation.

Absolutely wonder what century Sound Devices thinks they’re in.

It's particularly ironic to have that limitation in one of the most advanced field recorders on the market.

Although it was a freak occurrence that the split file had a one-time anomaly, that could escalate to be a disaster.

I hope you're able to get some input from Sound Devices and hopefully find out what caused that anamoly.

I think they’ll have a reply by mid-week unless they decide to decline a comment until they have updated their code and I won’t see it for another month. I was blunt with them about their code. Substituting my Wise 128GB card won’t make any difference.

They probably want me to retest so I’ll get a test done possibly Monday. I need to finish up that client work first but that won’t be done until tomorrow. Sure hope a 3 hour test is clean.

It would be terrible if this reoccurs on my next live music shoot during the performance of a song. If it happened during the chatter, not too bad, as I can edit it out.

I think they’ll have a reply by mid-week unless they decide to decline a comment until they have updated their code and I won’t see it for another month. I was blunt with them about their code. Substituting my Wise 128GB card won’t make any difference.

I hope that SD doesn't drop the ball on this... I think it's improbable because SD's reputation is built on reliability, but let's hope.

It would be terrible if this reoccurs on my next live music shoot during the performance of a song. If it happened during the chatter, not too bad, as I can edit it out.

Totally. Let's hope it doesn't.

Here is the response from Sound Devices which explains why the MixPre splits files:

“Before we continue, we should note that the max file size for a standard wave file is 4 GB.
This is because a wave file uses a 32-Bit unsigned integer to record the file size which can only represent a total of 4,294,967,295 bytes (which roughly equals 4 GB). It has been this way since Microsoft and IBM introduced the wave file in 1991, has become the industry standard.

In order to pass that 4 GB, we would have to follow the RF64 specification. I can note this as a request for the MixPre Series, but we cannot promise or guarantee this feature in future firmware.”

Here is the RF64 solution defined by EBU to replace the 32bit file size limit with a 64bit implementation for file size (which for practical purposes eliminates the file size limit) for Broadcast:

https://tech.ebu.ch/docs/tech/tech3306v1_0.pdf

I encouraged Sound Devices to be a leader and implement RF64 rather than follow the original .wav definition.

Anyone know how prevalent RF64 is throughout the industry? I don't.

It’s an EU broadcast standard I believe, Rakesh.

I got another email from Sound Devices that explains the gap in the project timeline using Tentacle timecode so there’s nothing going to affect anyone. An isolated incident and not a threat to the neighbourhood:

I always shoot 30 fps in the settings for the MixPre. And I always shoot 30 fps raw in my cameras. Somehow I accidentally and unintentionally selected recording in ProRes which would have been an errant finger touch I didn’t notice. The last time I used ProRes may have been a few years ago and at that time it was using 29.976 fps.

So another problem turns out to be due to operator error! Who knew I could make a mistake, eh? I don’t do that more than say three times a day!

I need to find the emoji for shame.

I did however continue to lobby for Sound Devices to implement RF64 with 64bit references for file size (which will never split another file in our lifetime). Who knows, maybe they’ll rethink their approach given it’s so easy to implement and they can take out their code creating split files.

PS
Sound Devices 8-series recorders have already implemented RF64. I have a feeling 6-series and MixPre II implementations of RF will occur in the future.

Rick

There are so many little things just waiting to rear their ugly heads and bite one ...

I have been pleased to see Custom profiles which can lock in settings one
uses regularly ... I always tend to show up very early and set up then
spend time looking for all the mistakes in the settings ... and my main
venue is a set which I do the lights sound and video ... and like a dog I
turn around at least three times before I can rest ... Each of those variables has
been dialed in ... and I still have days that surprise me.

The last time was when I connected my Deity Theos receiver to my 633 but swapped
the L and R inputs ... found it about half way through the session and an easy correction
in post ... added to my list of check twice ....

I have done the 23.976 to 24 fps mismatch ...

The 633 screen is tiny ... need to really concentrate when I run through the settings ...

No shame in being alive and thus subject to phases of the moon and our biorhythms ...
it happens ... always good to have a backup ... redundant recorder or second camera angle
to recover.

As you pointed out the split files aren't the issue ... good thing because my RED can spit out
hundreds of them in a session.

Thanks, Bob. I guess I can come in from leaning over the balcony railing and relax once again.

This last shoot was chaotic as people were constantly milling about and getting the audio set up required more attention so that I wasn’t diligently looking at the camera settings just before shooting began as a last minute verification. There was no intermission to change any settings as the fashions and music were non-stop.

Lesson learned though to double-check cameras just before rolling.

It’s an EU broadcast standard I believe, Rakesh.

Interesting. Has it seen adoption outside of EU broadcast? Or is the rest of the industry clinging onto antiquated standards like the crappy drop frame bogusness still?

I got another email from Sound Devices that explains the gap in the project timeline using Tentacle timecode so there’s nothing going to affect anyone. An isolated incident and not a threat to the neighbourhood:

That's a good sign!

I always shoot 30 fps in the settings for the MixPre. And I always shoot 30 fps raw in my cameras. Somehow I accidentally and unintentionally selected recording in ProRes which would have been an errant finger touch I didn’t notice. The last time I used ProRes may have been a few years ago and at that time it was using 29.976 fps.

Tapographical error... much easier to prevent than catographical errors, as all cat parents can confirm

Sound Devices 8-series recorders have already implemented RF64. I have a feeling 6-series and MixPre II implementations of RF will occur in the future.

If the 8 series already have RF64 then getting it in the MixPres seems probable, at leaest.

Does Resolve support it? I'm obviously not an audio expert, so I don't have any RF64 audio floating around to test it with

… If the 8 series already have RF64 then getting it in the MixPres seems probable, at leaest.

Does Resolve support it? I'm obviously not an audio expert, so I don't have any RF64 audio floating around to test it with

Perhaps BMD can confirm, but I’m not sure if the Resolve team has the time to read the Cinematography forum. I’ll post in the Resolve forum if a search doesn’t give us an answer.

PS
Yes, RF64 is supported. See post #3 by Reynaud in this Resolve forum thread:

Support for BWF, RF64 and BW64
https://r.tapatalk.com/shareLink/topic? ... source=app

This last shoot was chaotic as people were constantly milling about and getting the audio set up required more attention so that I wasn’t diligently looking at the camera settings just before shooting began as a last minute verification. There was no intermission to change any settings as the fashions and music were non-stop.

That is really a key point … if I am hurried distracted or not completely on point the potential for a less than ideal situation is magnified. Almost a Zen thing … and when I am focused I realize afterwards that I perceived little of the moment … only fragments of correct focus perspective color and sound levels … the resulting end result edit is where I can relive the moment and enjoy what transpired.