Some Sony receivers come with a Pulse Code Modulation setting to take advantage of the full sonic range that the PCM audio signal can deliver on Blu-Ray discs or high-definition TV shows. However, the PCM setting can cause audio problems when listening to standard definition content. Cable compatibility issues can lock some Sony receivers in PCM 48 mode.
Turn off the Sony receiver and all components connected to it, and then switch on the equipment.
Press the "PCM" button on the Sony remote control to switch off PCM mode. This will display on the LCD screen on the front of the receiver.
Play audio through the Sony. If it switches back to PCM 48 mode, the likely reason is a cable compatibility issue.
Check the back of the receiver, the television and the source signal -- such as a cable or satellite receiver -- to determine the component cable types. On a high definition system, a six-sided HDMI cable will likely connect the source signal to the TV or the receiver. An optical cable, which resembles a telephone line and plug, might connect the TV to the Sony.
Disconnect the optical cable from the back of the Sony receiver by pulling the plug straight out. Connect a standard stereo cable from a free set of input jacks on the Sony to the component, such as a TV, which is hooked up to the other end of the optical cable. The white and red plugs on the stereo cable connect to the matching colors on the left and right audio jacks.
Press the "PCM" button on the remote again, then retest the sound on the Sony receiver.
Switch out the stereo cable with an optical cable when listening to all-digital sources.
A receiver locked in PCM mode can affect playback of standard-definition audio sources, such as a DVD or standard-definition TV programs. When this happens, the receiver may not be able to process true surround sound and the audio may seem muffled.
Turn down the volume on the Sony receiver when connecting or disconnecting cables, then test the sound when the connections are complete.