Originally Posted by George Mills
Originally Posted by axle
A problem with testing for HD621 improvement is that the test has more than one variable. In addition to the HD621 as one variable you also have the interface as a second variable. The test with the HD621 requires the HDMI interface whereas the test without the HD621 requires the SPDIF.

Assuming the interface can be ruled out is a leap of faith. But this assumption is both reasonable and necessary to do the test.

Having said that, my experience is that you may not be able to notice the difference in a few minutes. But after listening to the HD621 all day then removing it, you will want the HD621 back in the loop.

To me, the most prevalent thing is better bass. Even aging ears should hear this. Second is less fatigue. I can listen at higher volumes all day long without the Joe's Garage scenario (mother screams "turn it down!")

I don't see your argument with interfaces. If anything HDMI will be worse and HD621 eventually transmits over SPDIF anyway (for 99.999% of us at the moment).

But I appreciate your honesty on what to expect and it's not something you toggle and immediately hear the difference. That is more believable than some other claims I've read.

However, I don't find my system fatiguing at all right now even at quite high volumes. I'm quite happy with that.

I would also think the whole apodizing thing has the least impact on low frequencies.

George, I have 2 comments to feedback

1) About the test itself, here is one possible A/B test:

A: VIP722 HDMI -> HD621 coax -> G68
B: VIP722 optical -> G68

Switching between A and B inputs on your G68 does not (cannot) provide a single variable test because the test switches the HD621 and also switches connector types. So how do you know that the improvement is due to the HD621 and not the connector? For the B test, E/O and O/E convserations add jitter. For the A test, you eliminate those conversions so you eliminate the respective jitter. But you may falsely conclude the improvement was due to the HD621 when in fact the the improvement was due to eliminating optical jitter. Same reasoning applies even if the B test used coax.

2) regarding the bass. I don't make any claims about apodizing. But I do claim that the lower the frequency and longer the note (descriptive of bass), the more it is susceptible to degradation over lower frequency jitter (wander). A PLL may not do much for this level of jitter. But a deep FIFO certainly will. I think that the HD621 deep FIFO is the reason that the HD621 improves bass.

Last edited by axle; 2010-02-02 18:55.
DSP6000, DSP5200, DSP5500VC, P300W, SW1600, G68, 568.2, HD621, G57, G55, Oppo BDP-105.