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Hi,
I’m trying to set this up but I can’t get a square wave.
Just to confirm, on page 7 of the test, you attatch the Pin 2 from printer port straight into the "tip" of the output from sound card? and pin 25 to earth of soundcard output?
Got the square wave working now, I had to tilt it to 27 to make it straight.
On the next test where you use BBP to generate the square wave to test the output under exciter load, the square was already perfect.
So do I just set BBP output tilt to 27 now?
Hi Modman!
Make sure you’re using a big (500 kohm or more) resistor as well, or you’ll get the wrong results.
Remember, the calibration utility is a makeshift oscilloscope, and the printer port is used only as a square wave reference (to calibrate the makeshift oscilloscope).
Thus, if the square out of BBP was already perfect, that means *no tilt correction is necessary* on the output — BBP’s output tilt should be 0!It’s not uncommon for really inexpensive sound cards (such as onboard) to already be DC straight. It basically means they saved another penny by not including an output coupling capacitor. Comes in very handy when you’re doing FM processing 😉.
///Leif
Makes perfect sense now…my Asus board (P5KPL-AM) already had perfect tilt. Thanks
I can’t use that tool to check for PEQ roll off can I? 🙂
MPX PEQ is generally the smallest problem of all. Rolloff means a slight loss of stereo separation, but if you don’t have an oscilloscope, that means you’re simply not that worried about squeezing 100% performance out of your system. Tilt correction alone will get you close enough. If you want to get all the way to 100%, just buy an oscilloscope — you can buy a good used one for under $100 on eBay.
The BBCAL tool only samples at 48 kHz, so it’s useless for MPX PEQ. Even if it did, you would still need a hardware Quicksweep generator, which (if even available) would probably cost thousands of dollars. Get a scope. If you’re a radio engineer, I can’t think of a good enough excuse not to already have one! 🙂
///Leif
I have my eye on a few Tektronix Scopes on ebay but they’re going for £120-200 here in the UK, still isn’t bad, I will be purchasing one.
I remember seeing a usefull guide that you wrote on converting an M-Audio 192 card with extra capacitors for perfect tilt.
Is this guide still online? and what are the benefits of this? I use the card for music production in the studio (recording etc..)
Would this benefit me on my recordings? 🙂Hi Modman!
The benefit is that it will solve the problem of tilt, as opposed to band-aiding it by pre-compensating in software. Will there be any audible benefit though, compared to properly calibrated pre-compensation (tilt adjustment in BBP)? Probably not. I really only did the modification in the name of thoroughness.
It will not audibly benefit your recordings unless you are referring to recording MPX straight from a tuner. 🙂
You can find the guide here:
http://mpxtool.com/site/hardware-sectio … 2-mod.html
Best,
///Leif
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