Echo Speech Corporation produces chips marketed by Analog Devices as the ``Personal Sound Architecture'', consisting of an Analog Devices AD2115 DSP, and an Analog Devices AD1848 CODEC. Boards based on this design are manufactured by Cardinal Electronics, Orchid, Wearnes, Western Digital (Paradise), and various other brand names that resell one of the above cards, typically for around $100. These devices support full duplex mode, but use DMA (to emulate the SoundBlaster) instead of the more desirable programmed I/O. (Bill Brackenridge)
If you hear the local microphone sound through the speaker or headset, mute the microphone in the Windows playback mixer.