The solution proposed in this technology is the development of a low-cost preamplifier device able to compose a stereo signal from two selectable mono signals, compatible with a wide range of signals. The device has also been designed so that the dynamic range of the output signal and its bandwidth are consistent with those of the input line of an audio standard acquisition card for personal computer.

It is believed that the input monochannel signals can have a dynamic range of amplitude and a bandwidth with different values. For example, let us consider that the most common microphones used for voice processing applications have a dynamic range of amplitude around ± 20 mV with a bandwidth less than 20 kHz, whereas the electroglotographic signal tends to vary between 0 and 1.5 volts, with a bandwidth less than 5 kHz. In the same way, line input of audio digitizing cards tends to have a dynamic range of amplitude of about 2 volts, allowing signals with bandwidth less than 22 kHz.

The adjustment of dynamic range is necessary in order to minimize the quantization error introduced by the capture card that plugs to the device described. Thus, the levels of amplitude of the resulting signal allow taking advantage of the dynamic range of amplitude of the digitalization later stage.

Thus, the types of input signals can be considered variable in terms of breadth and dynamic range of amplitude and bandwidth, while its application is limited by the maximum frequency of later stage of digitalization of the signal to be connected, and/or the bandwidth of the device.

Additionally, and thinking on those applications where one of the input signals comes from a microphone, the device has a subcircuit able to generate the phantom supply power, compatible with a wide range of microphone condenser models. This power supply consists of a continuous flow that is directly sent to the microphone by the input channel to supply the capsule. This solution enables the use of the device with quality microphones without using an external phantom power supply. Innovative Aspects: The main novelties of the device are related to the following characteristics:

" The microphone phantom power is incorporated in orly one device.
" It provide different levels of improvement for different types of measure.
" It provides calibration signals for measurements of power on the PC without using sound meters for calibration.
" Power supply via USB port avoids the use of transformers reducing weight, volume and cost.

The main advantage is the reduction of costs and size, as well as integration in a single device with additional functionality such as microphone phantom power supply and different levels of improvement.

The subsequent process of digitalization signals is carried out outside the same using commercial devices with very low cost. The end result significantly reduces the complexity and cost. It could be seen as a mid-range device.