The following lines were added (+) and removed (-):
Consumer rated line level is known as Hi-Z (high impedance) and, as stated above, operate at a -10 DBv level. There are also Hi-Z microphones available that use 1/4" plugs and operate at about -20DBv level. Some guitars and all electric keyboards are also Hi-Z.Professional devices typically use XLR and are considered balanced. These are Lo-Z and operate at +4 DBm level. There are Lo-Z microphones which will operate at approximately -50 DBm level.When a microphone picks up an acoustic sound wave, it generates a very small voltage waveform which is measured in microvolts. When a microphone picks up an acoustic sound wave, it generates a very small voltage waveform which is measured in microvolts. The line level signal needs to be reduced and impedance matched to send it to the microphone input of such a device. This will come with a cost. There will be a reduction in quality and impedance matching may be tricky. (Hi-Z, Z = impedance) Use a Pad! The line level signal needs to be reduced and impedance matched to send it to the microphone input of such a device. This will come with a cost. There will be a reduction in quality and impedance matching may be tricky. A great deal of attenuation is needed to match the signal levels. Consumer audio line (-10dBu) level to microphone matching can be done using a "40 dB L-pad attenuator". Professional audio audio line level (+4dBu) to microphone matching can be done using a "50 dB L-pad attenuator". L-pad, or simply a "pad" for short, is a simple circuit to accomplish the necessary matching. The pad is typically based on a configuration of resistors to create the necessary amount of attenuation. Pads can be designed to match or ignore impedance. The L-Pad is a type of pad design. A balanced T-pad (known as an H pad) has resistors in series with both sides of the input, and both sides of the output, but with a common resistor (R2) bridging the midpoints Radioshack offers an inline pad for an unbalanced, -10dBV source to go into a microphone input. The Radioshack part number is 274-300, the 40dB, RCA-to-1/8" mini-phone, in-line pad. You can create your own pad using resistors. Here is one example: [[File:audiolevelmatchingpad.png]] A simple 2 resistor model can be used. Attenuation in dB = 20 * log10((R1 + R2) / R2) [[File:audiolevelmatchingpad2.png]] The L-pad is the classic voltage divider circuit using two resistors to reduce the input voltage by some amount.