Abstract: An apparatus and method for maintaining a constant speech envelope using automatic gain control, wherein the level of the audio signal is monitored. If increasing, a first level of gain increase is applied to the gain signal. If decreasing, a second level of gain decrease is applied to the gain signal, the second level being less than the first level. By applying a lower level of change to the gain signal when it is seen as decreasing, a more constant speech envelope is obtained during gaps and interstices in the analog signal that are common in speech.

Abstract: A method of bonding a light polarizer having a metal sheet 4, 4-1 affixed to an end face thereof to a securing metal layer 5 involves bonding the securing metal layer 6 to the metal sheet 4, 4-1 by means of welding, whereby not only the working efficiency may be enhanced, but also long-term reliability in bonding may be ensured.