Digital voice transmission:

The high-speed multimedia modem would not deserve the name if it could not also transmit digital speech. Therefore, this possibility was also implemented in the menu item “Voice Audio”8).

Here the inputs and outputs of the sound card or, as in the example (Fig. 18), virtual audio cables (Virtual Audio Cable VAC) are selected.

One of the five operating modes can be selected at a time:

• Digital Monitor: the reception signal is looped through directly to the loudspeaker. This mode is used to observe the frequency or to evaluate the received signal.
• Internal Loop: the microphone is connected directly to the loudspeaker. This allows the function of the sound card and the volume settings to be checked.
• Codec Loop: in this test mode the selected codec is additionally looped in. This allows you to check the actual quality of the audio transmission at the different bit rates without going on air.
• Digital Voice RX: in this mode you can listen to a running Highspeed Modem QSO
• Digital Voice RX+TX: this is the actual QSO mode

If you offset Tx and Rx frequency by at least 5 kHz, true intercom (full duplex) is possible.

Here you can choose between two voice codecs. CODEC-2 works with a fixed audio rate of 3200 bps and is particularly suitable for low data rates. OPUS scales the audio rate in a ratio of 84 % to the data rate and offers a more natural speech quality at higher data rates (8APSK modes).