Troubleshooting S/PDIF Audio Issues

Escrito el por griquelme
Facebook Twitter WhatsApp LinkedIn

When connecting an LG TV to an external USB sound card via S/PDIF optical input for Logitech Z607 speakers, I encountered some significant audio quality issues. My initial suspicion fell on the hardware itself—specifically whether the optical cable was faulty or if the Pentium PC was struggling with the signal processing.

A view of an LG TV connected via optical cable to an external USB sound card, alongside a desktop PC and Logitech Z607 speakers.
The physical hardware setup for the S/PDIF troubleshooting session.

However, after carefully analyzing the diagnostic process and testing different digital formats, I realized my initial hardware assumptions were incorrect. The core issue wasn’t a physical failure of the USB card or the optical cable.

Digital Signal Processing

The investigation revealed that the LG TV’s ‘PCM’ setting works perfectly for stereo output because the signal is compatible with the sound card. However, when switching to ‘Pass Through’ mode, the TV attempts to send a compressed Dolby Digital (AC-3) or DTS stream.

Configuration Mismatch

The root cause of the problem was that the USB sound card lacks native AC-3 decoding capabilities. When the card receives this compressed Pass Through signal without proper software support, it manifests as distorted audio noise rather than a clean 5.1 surround mix.

A screen capture of a digital television's sound output settings, showing the selection of different audio formats like PCM, Auto, and Transferencia.
The TV settings menu revealing the difference between PCM and Pass Through modes.

Ultimately, the solution involves ensuring the TV is set to ‘PCM’ for stereo playback or finding an external decoder capable of handling the AC-3 stream before sending it to the sound card for analog conversion.