A sound processing host device comprising: a non-volatile memory that stores a sound signal processing program for a plurality of microphone units (2A, 2B, 2C, 2D, 2E), and the non-volatile memory being configured to be connected to one of the microphone units (2A, 2B, 2C, 2D, 2E) which are connected in series, and a speaker configured to emit a test sound wave toward each of the microphone units (2A, 2B, 2C, 2D, 2E), wherein the sound processing host device is configured to transmit the sound signal processing program read from the non-volatile memory to each of the microphone units (2A, 2B, 2C, 2D, 2E); wherein the sound processing host device is configured to receive a processed sound which has been processed based on the sound signal processing program; wherein the sound signal processing program is formed of an echo canceller program for implementing an echo canceller, filter coefficients of which are renewed, wherein the echo canceller program has a filter coefficient setting section for determining the number of the filter coefficients; wherein the sound processing host device is configured to change the number of the filter coefficients of each of the microphone units (2A, 2B, 2C, 2D, 2E) based on level data received from each of the microphone units (2A, 2B, 2C, 2D, 2E) with regard to the test sound wave emitted by the sound processing host device, to determine a change parameter for changing the number of filter coefficients for each of the microphone units (2A, 2B, 2C, 2D, 2E), to create serial data by dividing the change parameter into constant unit bit data and by arranging the unit bit data in the order of being respectively received by the microphone units (2A, 2B, 2C, 2D, 2E), and to transmit the serial data for the change parameter to the microphone units (2A, 2B, 2C, 2D, 2E), respectively; and wherein the host device is configured to transmit the echo canceller program in which the number of filter coefficients is increased to the microphone units (2A, 2B, 2C, 2D, 2E) located close to the host device and is configured to transmit the echo canceller program in which the number of filter coefficients is decreased to the microphone units (2A, 2B, 2C, 2D, 2E) located away from the host device. a non-volatile memory that stores a sound signal processing program for a plurality of microphone units (2A, 2B, 2C, 2D, 2E), and the non-volatile memory being configured to be connected to one of the microphone units (2A, 2B, 2C, 2D, 2E) which are connected in series, and a speaker configured to emit a test sound wave toward each of the microphone units (2A, 2B, 2C, 2D, 2E), wherein the sound processing host device is configured to transmit the sound signal processing program read from the non-volatile memory to each of the microphone units (2A, 2B, 2C, 2D, 2E); wherein the sound processing host device is configured to receive a processed sound which has been processed based on the sound signal processing program; wherein the sound signal processing program is formed of an echo canceller program for implementing an echo canceller, filter coefficients of which are renewed, wherein the echo canceller program has a filter coefficient setting section for determining the number of the filter coefficients; wherein the sound processing host device is configured to change the number of the filter coefficients of each of the microphone units (2A, 2B, 2C, 2D, 2E) based on level data received from each of the microphone units (2A, 2B, 2C, 2D, 2E) with regard to the test sound wave emitted by the sound processing host device, to determine a change parameter for changing the number of filter coefficients for each of the microphone units (2A, 2B, 2C, 2D, 2E), to create serial data by dividing the change parameter into constant unit bit data and by arranging the unit bit data in the order of being respectively received by the microphone units (2A, 2B, 2C, 2D, 2E), and to transmit the serial data for the change parameter to the microphone units (2A, 2B, 2C, 2D, 2E), respectively; and wherein the host device is configured to transmit the echo canceller program in which the number of filter coefficients is increased to the microphone units (2A, 2B, 2C, 2D, 2E) located close to the host device and is configured to transmit the echo canceller program in which the number of filter coefficients is decreased to the microphone units (2A, 2B, 2C, 2D, 2E) located away from the host device.