Input and Output Cables: What Plugs Where on Audio and Video Gear

Every audio and video device has ports labeled In and Out, and the most common wiring mistake is plugging a cable into the wrong one – a soundbar with no sound because its cable is in the TV’s Audio In instead of Audio Out, or a monitor showing no signal because the HDMI cable is in the wrong port. This guide explains what input and output mean on the devices you actually use, which cable belongs in which port, and the wiring pattern that makes any multi-device setup work on the first try.

What Input and Output Actually Mean

The terms are simple in principle and confusing in practice because the labels are not always obvious, and some ports do both directions at once.

The signal flow rule

Every cable carries a signal in one direction: from the device that generates the signal (the source) to the device that uses it (the destination). The source’s port is the output – it is sending the signal out. The destination’s port is the input – it is receiving the signal in. A cable always runs from an output to an input. Plugging a cable from an output to another output, or from an input to an input, does nothing: the signal has nowhere to go.

Ports that do both: pass-through and eARC

Some ports are both inputs and outputs. The TV’s HDMI eARC port is an input for the TV’s own content path and an output for audio to the soundbar – it is a bidirectional port on a single physical connector. A receiver’s HDMI pass-through receives a signal on one HDMI input and sends it out on another, so the same signal can feed both the TV and the receiver. Understanding which ports are bidirectional is the key to wiring a setup with more than two devices.

How to read the labels

Most devices label their ports clearly: HDMI In 1, HDMI In 2, Audio Out, Optical Out, eARC, Headphone Out, Line In. On a TV, the HDMI ports are HDMI In 1 through HDMI In 4 from the TV’s perspective – the TV is receiving the signal, so they are inputs to the TV. On a PC, the graphics card’s HDMI and DisplayPort ports are outputs – the PC is sending the signal to the monitor. When in doubt, the device that displays the picture has inputs; the device that generates the content has outputs.

Wiring the Common Device Pairs

The wiring pattern for each common device pair follows the signal flow rule, and once you know the pattern, any combination of devices is straightforward.

PC to monitor

The PC’s graphics card has HDMI and DisplayPort outputs. The monitor has HDMI and DisplayPort inputs. The cable runs from the PC’s HDMI out (or DP out) to the monitor’s HDMI in (or DP in). If the PC has both HDMI and DP and the monitor has both, prefer DisplayPort for the highest refresh rate. The audio, if the monitor has speakers, travels on the same HDMI or DP cable – no separate audio cable is needed.

TV to soundbar

The TV’s eARC HDMI port is the preferred connection: one HDMI cable from the TV’s eARC out to the soundbar’s HDMI in (eARC). The TV’s audio – from its tuner, apps, and other inputs – travels over that cable to the soundbar. For older soundbars without HDMI, use the TV’s Optical Out to the soundbar’s Optical In with a TOSLINK cable, or the TV’s Audio Out (L/R) to the soundbar’s Audio In (L/R) with red/white RCA cables.

Receiver in the middle: the home theater pattern

An AV receiver sits between the sources and the TV. Each source (console, streaming box, Blu-ray) connects to an HDMI input on the receiver; the receiver’s HDMI output connects to the TV’s HDMI input; the receiver’s speaker terminals connect to the speakers with speaker wire. The receiver processes the audio and sends video through to the TV on the same HDMI cable. The TV’s HDMI input that receives the receiver’s output is the one to select when watching any source.

Laptop to TV or projector

The laptop’s HDMI or USB-C (DisplayPort alt mode) output connects to the TV’s or projector’s HDMI input. The cable runs from the laptop’s out to the TV’s in. The laptop’s audio, if the TV or projector has speakers, travels on the same cable. If the laptop only has USB-C and the display only has HDMI, a USB-C to HDMI adapter or cable is required.

Common Input/Output Wiring Mistakes

Four wiring mistakes account for most no-signal or no-sound problems in a multi-device setup, and all four are fixable by re-reading the port labels.

Cable in the wrong TV input

The cable is plugged into HDMI 2 on the TV, but the TV’s input selector is set to HDMI 1. The fix is to change the TV’s input source to match the port the cable is in. This is the single most common no-signal cause and takes five seconds to fix.

Audio cable in the TV’s Audio In instead of Audio Out

A soundbar connected to the TV’s Audio In (L/R) port receives no signal because the TV is not sending audio out that port – it is receiving audio from an external source on that port. The fix is to move the cable to the TV’s Audio Out or eARC port. The In and Out labels on the same device mean opposite directions of signal flow, and mixing them up is silent: no error, just no sound.

PC audio not traveling over HDMI

A PC connected to a TV via HDMI shows the picture but no sound. The cause is usually the PC’s audio output setting: the PC is sending audio to its own speakers (or to a nonexistent headphone jack) instead of to the HDMI output. The fix is to change the PC’s default audio output device to the HDMI or DisplayPort output in the operating system’s sound settings.

Receiver HDMI pass-through not selected

A source connected to the receiver shows no picture on the TV because the TV’s input is set to the wrong HDMI port. The receiver’s HDMI output goes to a specific HDMI input on the TV – the TV must be set to that input to display any signal routed through the receiver. Check which HDMI port on the TV the receiver’s output cable is in, and select that input on the TV.

Input/Output Port Reference by Device

Real-World Application Scenarios

A home office PC setup uses one DisplayPort cable from the GPU’s DP out to the monitor’s DP in, and the audio travels on the same cable to the monitor’s speakers. A living-room TV setup uses one HDMI cable from the TV’s eARC out to the soundbar’s HDMI in, one HDMI cable from the streaming box to the TV’s HDMI 2, and one HDMI cable from the game console to the TV’s HDMI 1. A full home theater adds the receiver: three HDMI cables from the sources to the receiver’s HDMI inputs, one HDMI cable from the receiver’s HDMI out to the TV’s HDMI 1 (the input to select), and speaker wire from the receiver’s speaker terminals to the front, center, surround, and subwoofer drivers. A conference room uses a USB-C to HDMI cable from the presenter’s laptop out to the display’s HDMI in, with the audio traveling on the same cable to the room’s speaker system.

Recommended Internal Resources

Editorial Note: Internal linking recommendation: (1) Video Cables – https://zh-zong.com/video-cables/ (anchor: video cables); (2) Audio Cable Types – https://zh-zong.com/audio-cable-types/ (anchor: audio cable types); (3) Contact and Custom Cables – https://zh-zong.com/contact/ (anchor: custom cable inquiry)

Frequently Asked Questions (FAQ)