What is a (multichannel) seismograph?
Ground vibrations are detected by receivers called geophones placed (or planted) on the surface with an equal spacing. Each receiver's vibration
histories are transmitted in "analog" signal to a device called "seismograph," which then converts the signal into digital format solely for the purpose
of subsequent signal processing on a computer. For each receiver, therefore, a dedicated channel of analog-to-digital (A/D) conversion is
necessary. Such a device equipped with multiple A/D channels is called "multichannel" seismograph. In consequence, price of a seismograph is
directly proportional to the number of channels available. Also, the amplitude range of an analog signal that a seismograph can convert is directly
related to how accurately the original signal is preserved after conversion. This capacity is referred to "dynamic range" and determined by the
number of bits available in the corresponding hardware component executing the conversion. This can also influence on the price. Usually, a
relatively high (e.g., 24-bit) dynamic range is common for most multichannel seismographs used for conventional body-wave seismic surveys (e.g.,
refraction and reflection), in which signals are usually weak in comparison to noise warranting a high dynamic range. However, surface waves are
much stronger than body waves and, therefore, a seismograph with a relatively low dynamic range (e.g., 16-bit) can also be used for MASW surveys
without noticeable reduction in output quality. .