video time question...

[LUG]

Hello.

I've sped a song up using Quicktime in order to create a neat slow motion effect in Final Cut Pro.

I set the speed of the song to 1.5x in Quicktime and filmed the video in normal time just playing along to the faster track.

However, if I set my video to play at 50% speed in FCP I'm still out of sync with the video.

What is the math here? I know it's nothing difficult but for whatever reason it's not behaving the way I'd like things to.

I just need to know what speed to set the video to in order to get the most sync possible.

Thank you for any advice.

[Kurt Cowling]

Speeding up from 100% to 150% is a 50% increase, but slowing 150 back down to 100 is only a 33% decrease. Try setting to 67%.

[Kurt Cowling]

I should have said “a 1/3 decrease”. Set as close to 2/3 (66.6666667%) as your video app allows.

[stubbsonic]

Agreed.

Similarly you could increase to 133.33..% then slow down by 75%

If you needed more precision with the speedup or slowdown, you could use DP's pitch/time stuff.

Audacity is freeware and does pitch and time pretty well.

And my go-to is IRCAM TS

[mikehalloran]

Agreed.

Similarly you could increase to 133.33..% then slow down by 75%

If you needed more precision with the speedup or slowdown, you could use DP's pitch/time stuff.

Audacity is freeware and does pitch and time pretty well.

And my go-to is IRCAM TS

DP uses ZTX which is really good. I prefer using ZTX inside TwistedWave — same engine but far less convoluted to use when doing T/S math to match video.

I also have IRCAM TS. It and ZTX do not sound the same. Both are great but sometimes I prefer one over the other.

[LUG]

Thanks for the responses guys!

I realized that most of my problem was bad pantomiming to the original track. (Hard to appear to play correctly at such a speed!)

Either way, what is the breakdown of the math?

I get what the deal is but not 100% intuitively.

Wouldn't 150% be 50% faster than normal?

Thanks again.

[stubbsonic]

Either way, what is the breakdown of the math?

...

Wouldn't 150% be 50% faster than normal?

Let's use a simple example. Let's say the current speed is 2 (with an arbitrary unit). So increase the speed by 150%. Now the speed is 3.

Your new speed as now the new value for what is 100%. That old value of 2 as "100%" is no longer valid.

So now if you went to reduce that new speed back to it's original speed, you can't just subtract 50%-- because obviously that would be half of 3 (1.5).

2 is no longer 100%, it is now 3 that is 100%. So to get back to a speed of 2. So what would be the formula to get back?

[Kurt Cowling]

So what would be the formula to get back?

Hint... the answer was posted by me earlier in the thread.

[stubbsonic]

So what would be the formula to get back?

Hint... the answer was posted by me earlier in the thread.

Yes, we both arrived at the answer. The reason I asked a question about the formula was to create a little step-by-step process.

If a person had a tempo of X (in BPM), and they wanted to increase the tempo by a factor of Y (a percentage, perhaps), resulting in new tempo Z, then they want to revert tempo Z back to tempo X again, say by a factor of W (another percentage)-- is there a relationship between factors Y and W? Is there an elegant way to show all the ratios/relationships? My math skills are not great, but it's not for lack of trying.