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If your HDTV has only one HDMI input and you'd like to connect multiple source components, a simple video switcher will do the job. But if you'd like to upconvert lesser-quality signals (say, from a DVD player) to your display's full, high-def native resolution before they reach the TV, you'll need a scaler/switcher.

For example: Gefen has introduced the Home Theater Scaler ($400), a sleek, Mac mini-looking box that functions as a switcher and scaler for both analog and digital video signals. Along with letting you switch between a pair of analog component-video sources and two digital HDMI sources, the HTS uses dual scaling engines that convert video to the resolution of your choice, up to 1080p, as well as two 3-D motion-adaptive deinterlacers that help create smooth, film-like video from interlaced sources.

Inside the chassis, the most prominent features are the two main boards, which hold most of the chips and processors, and the internal wiring that routes signals from the inputs, through the various components, to the HDMI output. Each of the two HDMI inputs has separate digital-audio inputs and outputs (either coaxial or optical) so you can connect sources with DVI outputs. The two component-video inputs also have their own analog audio inputs.

The Home Theater Scaler's switcher functions are controlled by the included remote and an onscreen menu. Regardless of the input, output is via HDMI, with "mirrored" audio sent to the coaxial and optical digital-audio outputs.

There are two basic paths an input signal can take, depending on whether it's analog (component) or digital (DVI or HDMI). Component-video signals are fed through an analog-to-digital conversion (ADC) chip. The parallel digital video stream that emerges goes to the deinterlacers, if necessary, and then to the scaler chips, which convert the signal to the desired resolution and perform other image refinements such as color correction and noise reduction. Video is then sent to the transmitter chip, where it's serialized and embedded with the audio for HDMI output. The analog audio, which bypasses the scaler, is also digitized via an ADC chip and an encoder and then sent to the transmitter chip. The digitized audio is sent out via the HDMI connection, as well as via the separate digital-audio outs.

Signals from the HDMI inputs go into a receiver chip, which splits the serialized bit stream into data, video, and audio. Audio from the HDMI input bypasses the scaling chip and goes to a switch, enabling the user to select between the HDMI audio and the optical or coaxial audio inputs. It's then routed to the transmitter, where it's reunited with the video signal after scaling. The data channel goes to a microcontroller, which uses this information to set up the transmitter chip. The digital video (which is now a parallel digital video stream) is routed to the deinterlacers, if necessary, then to the scaler, and finally to the transmitter chip, where it's joined by the audio and data and re-serialized for transmission to your TV.

All this technology, of course, is virtually invisible, providing improved video from even standard-def sources, plus the ability to switch between various devices using a remote and an onscreen menu. And you don't even have to spring for the HDMI cable - one's included.

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