There has been a lot of discussion as to the proper levels of inputs and outputs to transceivers when working the new digital modes using a sound card either in VOX or PTT operation.  Many ask the question should I use/do I need an attenuator either into the sound card or out of the sound card into the transceiver.  I think the easiest way to approach an answer to that is to understand first that modern day transceivers are designed for inputs into the transceiver for SSB, FM, AFSK RTTY and the like to be at levels normally the same as seen when using a microphone.  If you are planning on using your transceiver for the new digital modes and driving the microphone input then the levels should be taken from the sound card should be comparable to the level outputs of your microphone.  While many sound cards have the capability to be set up for either high or low level outputs they are in most all cases providing outputs which are much to large for proper inputs into the microphone inputs  of the transceiver.  The way I set up my transceiver for operation of either AFSK RTTY, SSTV, and PSK31 is to first set up the transceiver for normal operation of SSB with speech processor turned "OFF".  After the microphone level is properly set for that mode I leave the setting alone and then concentrate on establishing a level out of the sound card which will properly drive the transceiver such that "NO ALC" is present when driving the transceiver.  This insures that I am not creating phase distortion by overdriving the inputs of the transceiver and/or overdriving the finals of the transceiver.  If you can not use the Control Panel of either WIN95/WIN98 to decrease the level of the output of your sound board to meet the above requirements then you need a resistive attenuator to decrease the output to the transceiver.  There is nothing wrong with using an attenuator except being hard headed about not using one.  If you want a good clean signal on the air then you should by all means do so.  If you will go to the Soundboard Interfacing portion of this site and review applications related to interfacing sound cards you will see proper use of attenuators and also of using variable resistors for level settings.

This now brings us to the aspect of proper levels of inputs into the sound card.  Again I recommend a review of  Sound Card Interfacing for the method of setting up the proper levels into the sound card to prevent overdriving the input circuits in the sound card creating phase distortion and causing excessive bandwidth of the transmitted signal. If you are taking the constant level output of audio from your transceiver and driving the sound card then you can rest assured you need to be very critical of levels into the sound card.  Review of your transceiver manual will normally tell what the levels are at the many inputs and outputs and will give you a good idea of need for attenuation of the inputs and outputs to the sound card.