Re: Well, THAT's Not Gonna Fucking Work!
I just want to say one more thing which I think is important. I have been thinking about this thread and all of the responses to it.
What made me reel at first reading this post was the 30deg laggy comment. This doesn't make any sense because phase vs. frequency doesn't mean laggy at all. In a non-physical sense, phase can be equated to instantaneous frequency, or "group" delay but nothing more. Phase does not add up as you move along the frequency axis. If you take the strict nonphysical definition of phase in relation to instantaneous frequency, then group delay is the negative derivative of phase. Every audio naive should know this by now. There are no sums involved in a derivative.
The second thing that made me confused was the fact I do not know where SMAART decided to set t0 after it conducted its measurement. I am assuming SMAART computed an impulse response from the measurement, then chose an appropriate t0 position, then computed the FFT to resolve the magnitude and phase curves displayed. Numerous other methods could have been used but none of them would involve an exact t0 for the phase measurement. They all depend on numerical devolution methods in some way or ‘transform’. I’m sorry I don’t really know much about these stochastic methods of measuring frequency response. I do assume that the same principles apply to them as deterministic stimuli. These methods work awesome for band limited acoustic signals when measuring loudspeakers but start to fail when the signal appears to fill the entire Nyquist bandwidth.
When measuring a DSP I would have pushed a frequency through the DSP and measured the phase relative at that one frequency simultaneously on the multiple channels. A stepped sine measurement if you will; Neither a Farina style logarithmic "swept sine" or MLS type measurement could be as exact as stepping with known and simultaneous signals over multiple wavelengths. This is especially true at the very low and very high frequencies. I have measured many pieces of equipment where the HF noise will correlate very well with the stimuli in the HF and cause an erroneous phase curve well before they will affect the magnitude response.
None the less, I am assuming SMAART turned out to be quite accurate based on the other posts which seem to support Bennett’s original measurement. So, sorry everyone, that I attacked the original post. I made some guesses about why this DSP might look like this. I just hope I get a chance to measure one myself at some point.
