You are probably referring to 'Stereo mix' or 'Record what you hear' depending on the audio device You could try using the 'Record> Classic Wave Driver' in Sound Forge You should first confirm the input mode in Windows sound settings. The Realtek interface usually list it as "Stereo Mix". I do not know it any of this will work in Sound Forge-3, which I used on the Windows 95 PC about a hundred years ago .. or so it seems.