Some notes on signal quality in a home theatre PC (HTPC)

My experience is that an analog tuner inside the HTPC is the worst option. An RF-modulated video-signal is a very complicated signal that needs quite advanced electronics to be “decoded”. This is because all the components of the signal is blended into one modulated signal. It needs to be separated in the tuner. This requires very accurate electronics and some quite high frequencies. The tuners built into PCI-cards in a PC are very often of a low quality and in addition to this they get interferrence from the other components inside the computer.

Actually, one could get better quality by using the analog tuner in a VCR and use composite video out of the VCR and do external tuning on the VCR through an IR Blaster like RedRat3.

A much better option is to use digital cable, digital satellite or digital terrestial. When using that kind of option you have three ways to get the picture from the Set Top Box into your computer:

The two most common:

1. Composite Video. In this signal all the colours are still blended into one signal and needs to be demodulated into sepparate colours. This demodulation always adds some noise. Unfortunately this noise is very bad for all the compression codecs that we use to store the video file.

2. S-Video. In this signal the colour and the black and white signal is transferred sepparately. This is a huge step upwards in quality. I experienced a quality that is close to twice as good as composite from the same set top box. I could meassure this by looking at the CPU-load and the estimated avaliable space on my disk when switching from composite to S-Video. With the same quality-setting in my PICVIDEO-codec I got half the CPU-load and twice the efficiency of the codec (= more video pr. megabyte on the disk).

Still not so common option:

3. RGB. Video input cards with RGB-capture are still limited to professional cards, but consumer-models are appearing right now. You can read about one of them here: SweetSpot

The best option (shortcut the Set Top Box entirely):

4. A digital decoder in your PC recording the broadcasted digital signal directly (like ShowShifter for DVB). This is still in an early stage but is the best option because you do not need to convert to analog and back to digital.

For those of you running ShowShifter on a big progressive screen or projector I think the SweetSpot-product mentioned earlier could give you a very good quality. I do not know how this product will work together with BeyondTV, Sage or MeedioTV.

For 16:9-recordings it is best to record the signal compressed horisontally into 4:3 and stretch it when displaying. This lets you use all the available lines in the signal (as opposed to recording a letterboxed signal).

And, by the way. My digital cable set top box does not deliver S-Video. My capture card accepts Composite and S-Video only. To get the best possible quality without investing in a professional level RGB-capture card I am using an RGB-to-S-Video converter from JS Technologies

Some notes on signal quality in a home theatre PC (HTPC)

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