Sometimes when utilizing a Bluetooth dongle (like the BTD 500 or BTD 800) Bluetooth dongle there may be a delay in the audio transmission.
The delay on Bluetooth speech/microphone transmission is caused by how the PC is utilizing the audio information it is being provided. For example when using the MM 500-X + BTD 500 in communication mode the two (2) devices toggle from the A2DP profile to the Handsfree Profile in order to run full duplex audio (this is not possible in A2DP). Here the latency is at about 20-40 m/s whereas the A2DP has latency of about 120 m/s so the issue is not latency.
When dongle is introduced for the PC the PC only sees it as a sound card with input/output and the usage of these interfaces chooses the profile to be used between the dongle and the headset. The Handsfree profile is activated when it sees activity on the microphone path (communications). Hence when there is a delay in the microphone audio the problem MUST be within the PC platform and how it chooses to use the audio resource. The way to alter/resolve this would be to adjust the PC settings and how it interfaces with the dongle.