BBP calibration tool

Hi, some of you had calibrated the Realtek HD Audio ALC888 card. This card comes onboard with a few motherbords. I can’t to run the tests for calibrate it. If someone have the tilt value for this card please share with us here. Thanks in advance.

It depends on the motherboard.

On the very cheapest motherboards, the manufacturer may neglect to even put a coupling capacitor in. Then, you’ll see perfect DC straight performance (although with a significant DC offset) and no roll-off whatsoever.

On more expensive motherboards though, the manufacturer helpfully puts a couple of capacitors in, but perhaps cheaps out and puts a small one in. Hello tilt, hello premature roll-off!

Funny how that works out, isn’t it? You just never know until you measure it for yourself. This is why I recommend to everyone: Buy a freaking oscilloscope!

A used oscilloscope is NOT expensive — you can find one on eBay for half the price of BBP. Compared to even the cheapest hardware processor, even counting a dedicated computer, a used oscilloscope, etc — you’re still saving a LOT of money, and getting the best possible performance.

Best,
///Leif

Hi Thagurt!

Positive Tilt (outwards tilt) basically never occurs, but if it does, you would correct it with a capacitor *in series*.
Negative Tilt can be corrected by adding large capacitors in parallel with the existing ones. To find which capacitor is causing the tilt, you will need to probe the circuit with an oscilloscope while running, to see where the tilt happens.

This is tricky when using on-board sound (since you must then probe a powered-on motherboard without crashing the computer) but it’s possible — I’ve done it.

Disclaimer: PROCEED AT YOUR OWN RISK. It is absolutely possible to fry your motherboard if you make a mistake! You have been warned.

You’ll need to take the computer completely apart and assemble it on the bench, using the minimum parts possible. You’ll need to be able to access the underside of the board (or sound card) while probing with an oscilloscope, and if using any pci cards they must be kept steady throughout the whole ordeal or the computer will just freeze. This can be accomplished with a rubber band, to lock the card leaning to one side.

Then:

Launch BBP and set it to output squarewave, and start by probing the output, making sure you see the tilt.
Look for electrolytic capacitors near the output. Probe both legs (while keeping the oscilloscope probe ground connected to the computer ground). If you find a capacitor where one pin shows more tilt than the other, then you have found a culprit. Add a much larger value capacitor in parallel with it, taking care to match the polarity. DO NOT remove the old one! It works even better with two in parallel, for noise filtering purposes.
After adding a capacitor, check the output again. If it’s flat enough, you’re done. Otherwise, look for more capacitors.

This is how I modified by M Audio Delta AP192 for near perfect squarewave performance.

Good luck!

Best regards,
///Leif