SDHC card read and write speeds

Merlin5

Merlin5

Merlin5

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Finchley, London
I'm looking for a 32GB memory card that will be fast enough for a new camcorder I'm buying. Not sure which one will be sufficient for my needs.

This is a bit long winded, so my apologies! Let me brief you on a quick spec and what I'll be doing. The camcorder is a Zoom Q8 which has built in high quality stereo condenser mics plus two XLR/TRS inputs for two extra mics or line-in. I'll be shooting video in 720p/60fps. The audio will be from the two built in mics. I'll also be connecting an extra microphone to one of the XLR inputs, and also feeding an audio track from a mixer as line-in to the other input.

Of the cards I've looked at, SDHC UH-1 seem to be faster than standard class 10 SD cards. OCUK has a Kingston 32GB SDHC UH-1 U3 90mb/s read speed 80mb/s write speed for a good price of £19.99.

I've also seen elsewhere a Sandisk Ultra UH-1 for £12 that I could go and pick up from a local shop today if I wanted. It has 80mb/s read speed. It doesn't specify write speed but a buyer on another retail site bought two of the 32GB Sandisk Ultra and did some tests. He got over 90mb/s read speed on both, but the write speed was 21mb/s on one card and 43mb/s on the other.

My question is, while read speed is obviously fast enough on the Kingston and the Sandisk, how much write speed do I really need? Would 20 to 40mb/s be sufficient given that I'm shooting video plus high quality 4 track audio? Another question is, are Kingston as good and reliable as Sandisk because it seems Sandisk are generally regarded as better.
 
Probably won't be sustaining writes of more than 2-3MB/s for video capture maybe a little more if you were doing 4K depending on the compression used by the camera. You might also find the camera hardware only writes at 19MB/s max anyhow as it seems to be the limit of the cheap and popular SD controller chipset a lot of consumer devices use.

That said in my experience SD cards seem to be optimised either for extremely high burst writes or sustained writing* and generally not optimised for both - I've used Kingston SDHC cards a lot in situations where I'm likely to be sustained writing i.e. data/video capture and they do well so far for me.


* I might be wrong here as I've not looked into it but I seem to remember the difference between the ultra and extreme is that the ultra is optimised for quickly dumping a lot of data like a high res photo over its ability to sustain writes while the extreme is more suited to continual writing like you'd get from video capture but at 720p that probably makes absolutely no odds.
 
Thanks breadturbo, yep I've seen the recommended cards list. But I'm sure there are more brands that are compatible.

Rroff, thanks. From what you're saying then, I'm going to have enough speed with the Sandisk Ultra.

By the way, the reason why I record in 720p is because it's the only resolution that offers 60fps which is a lot smoother. I don't think I really notice a lot of difference anyway between 720 and 1080. I wonder why 1080p/60fps isn't a thing yet. Or maybe it is.
 
Well I put my old 2GB Kingston SD card into the Q8 today and did a 30 second test recording in 720/60 and just using the built in stereo mics. Working great. It also gives me 16 minutes record time. And I discovered that this card is only rated 5mb/s read speed and 1.5mb/s write speed!

I don't know if recording for several minutes and adding two microphones to the XLR inputs will affect write speed, possibly not.

So you're right Rroff, seems it doesn't need a lot of write speed, nor read speed. I couldget by with this SD card but I'll buy an SDHC card anyway. 32GB would give me over 4 hours, way more than I need. Could go for an 8 or 16GB but the Sandisk 32GB is cheap enough anyway.
 
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