There is a high frequency noise in my sessions. I am using a Lexicon Alpha interface with Cubase 5 but now I can't record because of the noise. How can I solve this problem?

you SHOULD be able to.

Just use Direct Sound in the host tab.

Are you trying to use the mic input on the back or plugging it into the instrument input on the front? If you use a low impedance mic with a quarter inch instrument input cord, you would need a transformer adapter to make the mic work on high impedance. Even if you put it on line in, you would still have to convert it. Only the XLR socket on the back will work on a low impedance mic.

There is no activation code. You will need software that handles I/O sound device other than the built in audio of the PC. This device is sometimes delivered with either Sonar home edition or CuBase.

Sorry, but the Lexicon Alpha does NOT have Phantom power and you can't use a condenser mic with it without a Phantom power injector or preamp.
If you mean you have a Phantom power injector then it should be working. Do you have seperate mics for the two channels of the stereo? If you have only one mic, then only one side will record unless you set for mono recording and then dump the recording into stereo voa Cubase. I would recommend you get a small mixer... even a 4 channel one to use ahead of the Lexicon so you can mix and PAN your mics the way you want them. The recording and trying to control the panning in Cubase can be frustrating... The Lexicon really doesn't have anything built in to PAN the mic to the center when stereo recording. Small mixers are inexpensive and often you can find them used or in pawn shops for cheap.

First, I could NOT find an MXL99 microphone... IF you have an MXL990 microphone, you can STOP trying to have the Alpha read it because it won't !!! The MXL990 is a condenser mic and requires that Phantom power be supplied to it and the Alpha does NOT have Phantom power.
I have found a common problem on the audio interface inout is having to GO INTO the windows Sounds and Devices and verifying that under the VOICE tab, checking that the inout device is listed AND then checking the volume is turned up in that window... It seems like you have to verify everything and tweek a dozen places to get everything right to work. Having to look under the "VOICE" tab is not a good description of where the Alpha input control should be... so anyway, check that as well as it is not MUTED in that window. With Adobe Audition, make sure you set under the options, the "metering" to monitor the input recording level.

I suspect the problem is with the software setup in your PC. Verify all the options and also verify that the AUDIO system is assigned as stereo and assigned to the Lexicon for both in and out... Also check any "PAN" control settings. There is a possibilty that the Alpha has a dead channel...

Try putting a stereo signal into the 1/4 inch jacks and see if both record... if NOT then take it for repair under warranty... I had a Lexicon Omega that had a problem myself... warranty repair...

Sorry but... Very simply, you CANNOT use a condenser mic with the Alpha since it does not supply the required Phantom power for the mic. You must step up to another interface to use condenser mics. You can use dynamic mics with the Alpha or other audio sources. I use a Roland/Cakewalk UA25E interface with condenser mics and also the Lexicon Omega which does have Phantom power for the mics..

See if this info here will help you:http://www.lexiconpro.com/knowledgebase.php?product=7 Let me know if this helps.

http://www.lydrommet.no/artikkel/vis.php?id=37514try this click for the manual I have used it before for the same unit and the manual is here....Good luck Andy

Check for ground loops.

You MIGHT be able to cut the noise by setting the EQ's to clip the highs.