EMM-6 response, and system response, corrected

All my previous measurements of the EMM-6 microphone with various tweeters were wrong, because I had the Tact analog input sampling rate set to 44.1kHz instead of the 96kHz that I normally have it set to.  On Monday morning I started to think about the steep rolloff above 20kHz, and it occurred to me that could be the brickwall filter for a 44.1kHz sampling rate...and it was.  

For the longest time I had thought about something else, the bandwidth of the ATI 1502 power amplifier I use on the supertweeters.  It does not have quite the bandwidth of my Hafler 9300, Parasound, or Krell amplifiers.  But the power bandwidth is specified as 40khz, and I believe the small signal bandwidth is higher, 60kHz or so.  And that would be just the 3dB down point.  But even when Class AB power amplifiers roll off, they generally do not roll off like a brickwall filter.  Hmm, brickwall filter..

With this change, my system now peaks around 22kHz, and by the end of the calibration file for the microphone at 25kHz, the response is just a bit lower than the peak.  Then, where the calibration file ends, you can see a 4dB drop because there is no more calibration past that point, and that's where the serious rolloff begins.  The true response above 25kHz is much higher than shown, the microphone is seriously rolling off by that point without any applicable calibration.  (I intend to fix this by adding in an extrapolated microphone calibration up to 50kHz.)  Note that I also made this measurement with 96kHz sampling rate in ARTA and Focusrite, which is getting resampled by the Tact at 96kHz.  Most previous graphs were made with 48kHz 

The system now shows "useable" response up to 40kHz, which is barely lower than 12kHz.  If I had  calibration to 40kHz, it would be much higher than 12kHz.

FWIW the bass response is also "useable" to the limits of measurement shown here, about 13Hz, and probably down to about 8Hz or so.

("Useable" response means noticeable or something like that, which I would interpret as being roughly within the same  +/- 20dB window as the rest of system response.)

This measurement also shows the effect of yet another time alignment, performed on the evening of August 8, after I decided the time alignment done a week earlier and reported here a week ago, was wrong.  Some of the ideas in those articles were probably wrong also.  I plan to write an update on Time Alignment later today.

But you can notice here how the response from about 40Hz-300Hz is not perfect but stays within a clear range with uniformly spaced bumps, that are fairly small as these things go.  With something like octave averaging it  would be virtually flat.

This measurement was made with 10 averages.  Notice also the 0.1% distortion at 1kHz, rising gradually above that and below 200 Hz, but not above consistently above 1% until below 15Hz or so.