Video   V a r i e t y

"results are excellent - the ACE delivers the best pictures
of any consumer-level standards converter I have seen"

I frequently get to test various items of AV gadgetry for consumer electronics, but it's rare that I actually choose to buy any of them. The 300 ACE (Advanced Converter Enhancer) video processor from small Ipswich-based GTH Electronics proved to be an exception, however. This digital video processor is packed to the gunnels with all kinds of features that will appeal to moviemakers, home cinema enthusiasts and anybody who wants to make decent copies of tapes. It's not much to look at, having a definite home-constructor appearance with its Verobox-type enclosure and functionally designed front panel label. It's well made, though - inside, you'll find decent-quality components and glass-fibre PCBs. Where DIL ICs are specified, GTH has mounted them in sockets. The unit is powered by a 9V 500mA AC source, courtesy of a rather hefty transformer unit built into a mains plug. Round the back is a comprehensive bank of input and output sockets, including 4-pin mini-DIN connectors for S-video, phonos for composite video and audio, and a Scart socket that can be configured to work in various ways. A rear-panel switch allows you to specify whether your video source is composite or S-video The processed output is available in several formats (composite, S-video and/or RGB or even YUV).

All of the ACE's features are controlled by a sizeable quantity of knobs and pushbuttons on the front panel. The most important feature is undoubtedly full standards-conversion between PAL (50Hz, or the 60Hz variety generated by some VCRs when playing NTSC tapes), SECAM, and both 3.58MHz and 4.43MHz flavours of NTSC. The feature can be very useful if you want to swap tapes with overseas video enthusiasts, watch NTSC DVDs or laserdiscs on older TVs, or record foreign TV programmes from satellite TV. Combine the ACE with a multi-standard VCR (Thomson do a good 400 one with hi-fi sound and a stereo tuner) and you've got a pretty-flexible world-wide video solution. Note that the input standard is selected automatically, but I've had no problems here. Four buttons allow the output format to be selected. Two on the left select the colour standard (NTSC, PAL or SECAM), while the pair on the right selects the refresh rate (50 or 60Hz) and NTSC/PAL colour subcarrier frequency (3.58MHz or 4.43MHz). Although some other domestic-grade standards converters are available, none of the ones I know of will convert to SECAM. Although one or two have a SECAM input, they will only convert to PAL or NTSC.

Standards conversion works by digitising the Y, U and V components of each field and storing them in a high-speed memory. It's then read out at the desired field rate, which is generally 50Hz for PAL or SECAM, and 60Hz for NTSC. At the same time, scanning lines are removed (when going from 625 to 525 lines) or added (when going from 525 lines to 625 lines). The processes involved here are rather complex, to prevent the aspect ratio from being screwed up. Adding lines in particular is rather difficult, and most converters employ an interpolation process to fill in those missing lines. The converted Y, U and V components are then recombined. Professional standards converters offer various tricks to reduce motion 'judder', which can be rather noticeable if scenes containing fast motion are converted. A common trick is predictive compensation, which borrows heavily from work carried out on MPEG video compression systems. The ACE doesn't have such tricks - after all, it costs 300 against the 10,000-plus of broadcast-standard converters. That said, results are excellent - the ACE delivers the best pictures of any consumer-level standards converter I have seen, including a Taiwanese one that sells for twice the price and misses out on most of the ACE's features. Pictures are crisp, and miss out on colour bleed. Note that the ACE has 8Mb of field memory against the 2 or 4 of competing units. As a result, it will cope with a full-resolution frame without the need for compression.

Note that if the output standard is selected to match that of the input, the ACE will act as a timebase corrector. Such devices are very useful if you're trying to make stable copies from worn tapes that exhibit obvious drop-outs. As an added bonus, it will also defeat the Macrovision copy-protection, which is good news if you want to make a 'back-up' of a damaged pre-recorded tape. (GTH Note: We have a strict policy on this. See FAQs) Another very useful feature for 'copyists' is the colour shift control. This modifies the horizontal position of the colour relative to the brightness, and it's thus possible to bring the two back into registration with each other and thus avoid colour 'bleed'. It's provided to correct multiple-generation copies, where displacement between the chroma and luminance signals isn't uncommon, owing to poor equalisation of the signal delays encountered in the VCR's signal processing paths. You also get vertical colour-shift correction. This was added to compensate for some modern VCRs, which apparently introduce such errors!

Also on offer are colour correction (there are separate red, green and blue level controls) for compensating camcorder white balance errors, video adjustments (contrast, brightness, colour saturation/hue and sharpness controls) and a video/audio fader that can be operated manually or automatically over an adjustable period. You can also invert the video signal, which can be useful if you want to get negatives onto video with your camcorder and an appropriate light source. The ACE also offers some 'standard' test patterns. In addition to EBU-standard colour bars, you get 'red' and 'blue' purity screens. These are useful for checking the purity of TV screens, and assessing whether they need degaussing. They're also very good for (roughly) assessing the chroma signal-to-noise ratio of a VCR. Note that these signals are available in any TV standard making the ACE ideal for assessing and configuring multi-standard colour decoders.

The rear-mounted Scart socket provides additional composite/S-video outputs, and can also be switched to deliver additional RGB or YUV (component) video outputs. The ACE can thus be used as a multi-standard colour decoder for PAL-only TV sets with a RGB Scart input (cheaper than replacing older rear-projection TVs, I suppose!). The YUV output can drive some new projection monitors and plasma screens, and has obvious interest to anybody who wants to transfer S-VHS footage to broadcast-spec (e.g., Betacam) recorders. Once again, the picture quality is superb (note that a digital comb filter ensures a crisp picture with no fuzzy edges). Supplied with the unit is a 4-pin mini-DIN to twin phono adaptor-cable, which allows the ACE to drive two composite video outputs in the appropriate mode. As a result, the ACE can act as a distribution amplifier capable of feeding up to 4 VCRs or monitors.

Inside the ACE, all of the circuitry is on two neatly-designed PCBs. The first is the main board, which contains most of the circuitry, controls and socketry. The second board, which is mounted on the front panel, contains another row of controls. On the underside of the main PCB are the surface-mounted video ADC and DAC, which are sourced from Philips. Both of these chips are commonly encountered on video capture cards, of the type used for PC-based non-linear video editing. According to GTH, these chips - which have an exceptionally-fine lead-pitch - were carefully hand-soldered to the board. As the photos show an excellent job was done. There's hope then for the rest of us, who are forced to use surface-mounted components because their through-hole equivalents simply do not exist! On the component side of the board is a (socketed) Xilinx 80MHz FPGA which has been programmed to provide many of the more complex video features. The controls and operation of the unit are looked after by a PIC. In all, the ACE is a fabulous piece of equipment - and proof that a small and innovative company is capable of beating the major corporations at their own game!

Martin Pipe welcomes comments and ideas.
E-mail him Or look out for him online! His ICQ ID is: 15482544

ELECTRONICS and Beyond, March 2001.

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