Why shouldn't I use ReClock with SP/DIF output?

[cbemoore]

Watching PAL DVDs?
Here's why you need ReClock: http://www.schmidt-web.info/malte/english.html

If you don't hear the difference, don't download ReClock

From James' comments, he seems to assume that the only use for ReClock is PAL Speedup correction. If that's why you're using ReClock, then I agree you should use analog out as he suggests.

However, I'm not interested in PAL Speedup correction. I simply want to remove video judder by precisely matching my video fps to the screen refresh rate. I believe this was also Ogo's original aim when he started ReClock development.

As an example, I've set up the ReClock VB script so that when I play a 24fps video, my screen's refresh rate automatically changes to 72Hz. ReClock then keeps the video locked to exactly 3 refreshes per frame.

If I use SP/DIF output, I occasionally get a dropped audio frame here and there (but not many, because my refresh rate is already close to the desired value). These dropped audio frames are inaudible to me, so I don't notice any problems using SP/DIF output.

I realise I could use the built-in AC3 encoder, but then the audio chain would be something like:

DTS bitstream -> DTS decoder -> PCM Audio -> ReClock -> Resampled PCM Audio -> AC3 Encoder -> AC3 bitstream -> SP/DIF to receiver

Will this decoding, resampling and re-encoding really give me better audio quality than the occasional dropped frame?

 

[James]

From James' comments, he seems to assume that the only use for ReClock is PAL Speedup correction. If that's why you're using ReClock, then I agree you should use analog out as he suggests.

However, I'm not interested in PAL Speedup correction. I simply want to remove video judder by precisely matching my video fps to the screen refresh rate. I believe this was also Ogo's original aim when he started ReClock development.

As an example, I've set up the ReClock VB script so that when I play a 24fps video, my screen's refresh rate automatically changes to 72Hz. ReClock then keeps the video locked to exactly 3 refreshes per frame.

If I use SP/DIF output, I occasionally get a dropped audio frame here and there (but not many, because my refresh rate is already close to the desired value). These dropped audio frames are inaudible to me, so I don't notice any problems using SP/DIF output.

I realise I could use the built-in AC3 encoder, but then the audio chain would be something like:

DTS bitstream -> DTS decoder -> PCM Audio -> ReClock -> Resampled PCM Audio -> AC3 Encoder -> AC3 bitstream -> SP/DIF to receiver

Will this decoding, resampling and re-encoding really give me better audio quality than the occasional dropped frame?

No, it will give you no occasional dropped frames. In no way will the quality increase. But it won't decrease as much as some people think.
And you don't need to precisely match input and output frequencies. In your example it won't matter if the input frame rate is 23.976 or 24fps, your refresh rate of approx. 72Hz will be fine. Otherwise you would need very precise refresh rates for every possible input frame rate, like 71.928Hz. Certainly possible with tools like PowerStrip, but these introduce their own share of problems, e.g. no audio over HDMI with ATI cards. And with (some) modern LCOS/DLP/LCD projectors these timings can be tricky, as some will introduce tearing if you feed a frequency they don't like. Or they won't sync at all. Users of CRTs will have better luck.

As a general rule, I recommend to avoid SPDIF pass through. If it works for you and if you're happy, feel free to use it. At least the option is there.
According to the changelog Ogo's "original aim" is about 6 years old. With modern equipment, projectors, HDTV, HDMI audio, displays with "fixed" refresh rates using SPDIF passthrough is simply unpractical.