Hi,
if u r using windows platform, the use the Windows SDK to access the sound card and get voice signal samples,
more specifically, Windows SDK provided access to ur sound card functionality via the Windows Multimedia SDK and this has the total Multimedia sdk, i think u need to use Multimedia Audio sdk, this has a sdk component "Waveform Audio" and this sdk provide u functions to access, record and play voice signals,
if u have installed windows plaform sdk then look for "waveInAddBuffer" or waveInxxxx() functions and u r on ur way.
one more thing u need to figure out how to call the winapi functions from delphi if u have not called them before, read the delphi compiler documentation.