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Matt Whittemore
Another "which should I buy" post
on Sep 6, 2016 at 1:19:51 am

Hey there, I was wondering if there is much difference between an i5 and an i7?

I'm also wondering about differences in the following graphics cards: AMD Radeon R9 M290X, M390, and M395.

I need to get a second iMac and was looking at the refurbished ones (the 5k ones with the Fusion drive). They're all i5's. My current iMac is a 3.4GHz i7 with NVIDIA GeForce GTX 680MX 2048 MB and it works great for what I do. So now I'm wondering if I should just get a new (non-refurbished) iMac with an i7 or if the i5 (3.2GHz, 3.5, 3.4) will be good enough. I realize that there are a ton of variables like GHz and whatnot, but thats what's making it a tough decision. It gets me every time I need a new Apple product.

I'm running FCPX, mostly 1080p but will probably need to edit 4k in the near future. I do lots of multicam with footage from C100's, 5D III's, GoPro. Any thoughts would be appreciated.


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Noah Kadner
Re: Another "which should I buy" post
on Sep 6, 2016 at 3:44:29 am

Hard to say without knowing how tight your deadlines are and how dense your projects become. Obviously the more machine you can afford the better.

Noah

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Joe Marler
Re: Another "which should I buy" post
on Sep 6, 2016 at 12:38:51 pm

[Matt Whittemore] "I need to get a second iMac and was looking at the refurbished ones (the 5k ones with the Fusion drive). They're all i5's....I'm wondering if I should just get a new (non-refurbished) iMac with an i7 or if the i5 (3.2GHz, 3.5, 3.4) will be good enough...
I'm running FCPX, mostly 1080p but will probably need to edit 4k in the near future. I do lots of multicam with footage from C100's, 5D III's, GoPro..."


For 1080p almost anything will work. For 4k almost nothing is fast enough. Multicam 1080p H264 may require transcoding to proxy for smooth performance except on the highest-end machines. Multicam 4k definitely requires proxy, which in turn means your storage requirements are much larger since proxy is roughly doubles the storage requirement vs camera-native H264, but that's better than optimized media which is about 8x the size.

Re i5 vs i7, in narrow cases the i7 hyperthreading feature can improve performance. I used the 3rd-party CPUSetter utility to disable/enable hyperthreading, and this made about 30% difference in FCPX export speed to H264. In other workloads such as Lightroom import and preview generation, it made no difference.

However the i7 on current top-spec iMacs is 4Ghz, so that is 21% faster (excluding turbo boost which is unpredictable) for all CPU tasks than the 3.3Ghz i5 version -- independent from any hyperthreading benefit.

Nice as the retina screen is (and I wouldn't want anything else) there is some difficult-to-quantify performance penalty from the high resolution. In side-by-side testing of my 2013 top-spec iMac 27 (non-retina) and 2015 top-spec retina iMac 27 in both Lightroom and FCPX the retina version can be a little sluggish in some tasks. This might be the timing controller (TCON) or bit-block-transfer overhead. However this is a moot point since getting the top iMac 27 requires a retina screen. But if you can get a good deal on a 2013 iMac 27 with i7, those work very well and are affordable. But the retina screen is dramatically superior, especially for text.

Re Fusion Drive vs SSD, I've tested that extensively and don't see much difference in real world workloads, whether it is application launch speed, boot speed, or smaller FCPX projects that would fit on the system drive. With multicam 1080p and especially 4k, you generally have your content on an external drive so the system drive isn't doing much. IOW the high I/O rate of SSD doesn't help much since you aren't pushing it that hard anyway. I've seen lots of people get carried away with specs, get a too-small SSD system drive, then hit problems because they ran out of space.

The main issue is 4k. Really this should not be a shock since it's 4x the data and would require a computer 4x as fast to provide the same perceptual performance on 4k vs 1080p. A fast GPU helps but a lot of the code paths (ie H264 encode/decode) are not amenable to GPU-style parallelization.

This creates a situation where we're knocked back years in time and again have to transcode everything for adequate performance. This hurts after getting used to editing camera-native files at DV, 720p and 1080p. It also implies you'll need plenty of fast I/O, not some puny USB bus-powered 5400 rpm drive.


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