Don’t skimp on the Media

Categories: Media 3 Comments


SDXC cards are at a price that you would be a fool not to buy them over SDHC cards. A 64G SDXC card is now £26 and that’s a UHS Speed Class 3 card fast enough to record 4K.


It’s important to remember how flimsy a normal SD card actually is and it does not take much to unhinge the memory from the board. Everything is spot welded and there are over 40 miniature welds per wafer underneath the two memory boards, the act of dropping the card on a hard floor is enough to cause irreversible damage.


One of my regulars, Charles, has given me a more precise update on cards and their speeds, over to you Charles…

“Both the C class and the U class are minimum sustained write speeds which is the important one for video as this must be higher than the video stream rate to stop drop outs.

The C class is the traditional SD card databus and the U class is the newer UHS databus.

If you put a UHS capable SD card in a non UHS capable device it will fallback to the traditional databus. UHS cards can be marked with a C class as well for this reason as your Panasonic is, but it’s not essential as it’s an unusual situtation.

UHS itself has two versions markeds as an I or II after the SD logo. The later II variant has additional pins to make the bus wider but will work as a I if the devuce does not use them. Currently the U class is the same in both but in future it’s likely that II cards will support higher U classes that I cards cannot.

It is unfortunate that there are no standards around marking cards with maximum burst speeds as read is often much faster than write. The Panasonic card is being very clear, the SanDisk isn’t leading me to suspect that is actually a read speed.

Nevertheless on markings those are equivalent cards and the SanDisk likely the faster one and is certainly using the later UHS spec.

There are still very sensible reasons to stick with the cards that are marked in the manual as compatible, especially with early firmware in new devices and especially for paying jobs, but those tend to be due to unexpected interactions between card and device chipsets that often only surface in the field. After all the price difference is likely negligable compared to other costs unlike SD vs SxS.

Long term I strongly suspect a device like the GH4 will get a lot of testing by enthusiasts who will build up references of which other cards work well as in my experience manufacturers rarely update compatibility lists once the device is in market with stable firmware.

More detail on the speed standards at the SD Association, something everyone relying on SD cards for work should read

As an aside certainly for HD work I think SD cards are now cheap enough to treat them like tape used to be ie used once and then archived with the cost factored into the job. A fire safe of ‘originals’ at a different location to your mainline storage certainly makes sense.”

This is fine for testing the water or personal use but if you are a professional working with a paying customer don’t skimp on your media to save a few bucks.

If Panasonic tell you that you need UHS Speed Class 3 cards then thats what you use for 4K its that simple, anyone filming otherwise is a fool and remember it will come back to bite you when you least expect it if you don’t follow the simple rules.

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3 comments on this post

  1. Jeff Garmen says:

    This article is very helpful in explaining the nomenclature currently applied to SD cards.

    And from an application perspective, I certainly agree that as the GH4 hits the streets, that we will see numerous reports from users as to the various results achieved from the different SD cards available. But I needed to know where to start and this article helps with that.

    One card I am particularly interested in, and that still confuses me, is the SanDisk Extreme Pro SDXC UHS I Class 10 at 95MB/s. The published speed certainly exceeds 30MB/s required for a U3 rating, but this card is actually rated at only U1. I have already read a user report that this card has no problem with 4K on the GH4, but the rating numbers don’t square.

    I normally use SanDisk, but for my initial GH4 4K trials, I picked up several Transcend UHS I U3 cards, ironically, with a lower data write speed than the SanDisk card above which isn’t labeled to meet the U3 spec.

    Time will tell.

  2. Dave says:

    Curious if anyone knows how the simultaneous photo mode impacts the data rate, bandwidth and fragmentation of the 4K stream on the GH4. Also does anyone know why there was a limit on the GH3 for still images (I think it was 30) while taking video? I have also experienced a delay on my GH3 as it continues to write a file after I stop recording and sometimes cannot shut the cam off. Was using the 64GB SanDisk Extreme Pro 95MB/s cards. kicking off GH4 with SanDisk U3.

    • Bertie says:

      The OPENSTEP PreipctBujldor.aep didn’t do parallel builds, but it also didn’t run on multi-CPU hardware. The Mac OS X 10.0 Project (note the space, it’s also sometimes referred to as “Project Builder X” since it was a from-scratch rewrite for Mac OS X) is what used jam, and it could do parallel builds.

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