Some video cards based on graphics chips from nVidia have an SPDIF input connector. In this tutorial we will teach you when this connector should be used and how to use it.

This small connector present on some GeForce cards allows you to use only one instead of two cables to connect your PC to your home theater setup. If you won’t connect your PC to an HDTV or if the use of two separated cable doesn’t bother you, you don’t need to make the connection we will describe in this tutorial and you can stop reading this tutorial right now.

SPDIF is a standard used to transmit digital audio.

The purpose of this small connector is very simple: it is used to allow digital audio to be routed to the HDMI output. All video cards have one or two DVI connectors, and any DVI connector can be converted into an HDMI connector by the use of a simple adaptor. The problem is that the DVI connector does not transmit audio signals, only video, while HDMI can transmit both audio and video. If you don’t have a clue of what we are talking about please read our Video Connectors tutorial.

So if you convert a DVI connector into HDMI to connect your video card to your HDTV, you will only get video on your TV. The audio must be transmitted using a different way. The most common way to connect your PC to an HDTV is to convert the DVI connector into an HDMI and then use your analog PC speakers to get the audio or connect your PC to your home theater receiver thru an SPDIF cable, getting audio from your home theater speakers. In other words you will need at least two cables, one connecting the video (DVI-to-HDMI) and another connecting the audio (SPDIF out from your PC to SPDIF in from your home theater receiver). See Figure 1.

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Figure 1: How typically a PC is connected to a hi-def home theater system.

If you want your PC HDMI output to transmit the audio being generated by your PC (e.g. the audio from a video that you are playing), you will have to manually connect a cable from the SPDIF output from your sound card (usually a connector on your motherboard) to the SPDIF input located on your GeForce video card. It is important to notice that AMD claims that video cards based on their Radeon graphics chips already provide support for audio on the DVI/HDMI connector, not requiring any cable to be connected (this connection is done thru the PCI Express bus and it is invisible to the user).

You will only need to make this connection under two scenarios. First, if you want to connect your PC to your HDTV and want the audio to come from the TV speakers for some reason. Notice that most people that have an HDTV also have a home theater receiver with a 5.1 or 7.1 surround sound and if this is your case, you don’t want the audio coming from the TV speakers, but coming from the surround speakers.

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Figure 2: First scenario.

The second scenario is that you have a home theater receiver or an HDTV set with a built-in audio/video switcher that is capable of separating audio from the HDMI connection.

Usually at home we have more than one video source. For example, most people have at least two video sources: a cable/satellite TV decoder and a DVD/Blu-Ray/HD-DVD player. If you connect them into separated inputs from your TV and connect their audio output to your home theater receiver, you will have to perform two tasks every time you want to switch between them. You will have to select the video input on your TV to get the correct image and select the audio input on your home theater receiver to get the correct audio.

One solution most HDTV sets have to prevent you from having to switch audio inputs on your receiver is an SPDIF output. This output is then connected to the receiver SPDIF input and the TV will automatically route to this output the correct audio source according to the selection you made. On this case the video selection is done on the TV set. We illustrate this case on Figure 3.

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Figure 3: HDTV set with SPDIF output.

Another solution is to use a receiver with a built-in switcher, so everything is connected to the receiver and the receiver will send to the TV the appropriate video signal, while it handles the correct audio signal. On this case the audio/video input selection is done at the receiver and the TV is configured to always use the same video input, the one that is coming from the receiver. We illustrate this case on Figure 4.

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Figure 4: Home theater receiver with audio/video switcher.

As we mentioned, if your PC doesn’t provide audio signal on its HDMI output, you will need two cables: one cable for the video signal and one cable for the audio signal. If your HDTV (first configuration) or home theater receiver (second configuration) are capable of extracting audio from the HDMI connection then instead of two cables you can have just one HDMI cable connecting your PC to your home theater setup if you make the connection we will describe on the next page.

On the first configuration (Figure 3), the HDTV would get the video from the HDMI cable and route the audio from the HDMI cable to its SPDIF output, while on the second configuration (Figure 4) the home theater receiver would get the audio from the HDMI cable and route the video to your HDTV set.

Notice that if your HDTV set or receiver aren’t capable of extracting audio from HDMI to re-route it to a different output you will still need to use two cables to connect your PC to your home theater setup.