Product Review -
Yamaha DDP-1 AC-3 Processor - November, 1995 (Replaced by DDP-2, 1998)
By John E. Johnson, Jr.
Yamaha DDP-1 AC-3 Processor; Inputs: RF, Coaxial, Optical; Outputs: Mains - left/right, Center, Rear - left/right, Subwoofer; Output level: 2V (6V Subwoofer); Frequency response: 20 Hz - 20 kHz plus or minus 1 dB; Harmonic distortion: less than 0.01% at 1 kHz, Size: 5"H x 17"W x 14"D; Black metal chassis, Weight: 13.5 pounds; $599; Yamaha Electronics, 6660 Orangethorpe Avenue, Buena Park, California 90620, Phone (714)-522-9105.
Well, the home version of AC-3 is here, and the waiting is over. Speculation is done, the cards are on the table, the horses have crossed the finish line, and the champagne is being poured. Was it worth the wait? You bet!
This is the first AC-3 unit we have tested, and our hearts were racing as we powered up. Would full range stereophonic sound to the rear be too much to handle? Would it have audible degradation from the data compression? Read on.
The DDP-1 is an outboard processor. This means that you need additional electronics to make it work. Of course, you must have an AC-3 equipped laserdisc player to start with. These players have an RF output on the back, which must then be connected to the RF input on the DDP-1. The connections are via a single audio cable with RCA plugs on both ends. A good coaxial audio cable will do (not supplied with the unit). Here is where some confusion may arise. There is also a "coaxial" input on the DDP-1 which looks just like the RF input (RCA jack). The coaxial input, and the optical input, are "for digital signals . . . and provided for future use" (DDP-1 instruction manual). Presumably, this means DVD (Digital Video Disc) AC-3 signals, or HDTV AC-3 signals, which will be digital direct rather than RF.
Perhaps now would be a good time to discuss this RF business, as we have seen some confusion on the BBS threads. In order to make the AC-3 signal backward compatible with existing laserdisc production technology, the right analog channel was assigned to carry the AC-3 data. In older model laserdisc players, there were only the two analog audio channels (left and right stereo) and video, while the newer players have not only the two original analog audio channels with video, but two digital audio channels (similar to CD) as well. The video and two analog channels are handled much like a television broadcast transmission, in that the signal is embedded (carried) in a carrier frequency wave by modulating that carrier up and down in frequency as the data signal varies. This is called frequency modulation (FM). The decoding process involves "demodulation" of the carrier, removing the carrier frequency itself, leaving the data signal (video and sound). Since AC-3 from laserdisc is in the right analog channel, it must be demodulated before it can be decoded into the various discrete surround channels (Main left/right, Center, Rear left/right, and subwoofer - low frequency effects) for amplification. Thus, AC-3 output from the laserdisc is a 2.88 Megahertz RF (radio frequency) signal that is sent to the processor (the RF input on the processor), where it is demodulated and decoded. If you have an older laserdisc player with just the analog audio channels, you will hear an odd sound from the right channel when you play an AC-3 laserdisc. That's your player attempting to convert the 384 kilobits per second AC-3 bitstream into an analog waveform (music). This analog waveform representation of the AC-3 bitstream cannot be AC-3 decoded. So, in order to get at the AC-3 digital bitstream properly for decoding, it must be sent out in its RF modulated form, where it is then demodulated into a digital bitstream for AC-3 decoding by an AC-3 receiver or outboard AC-3 processor.
The DDP-1 was designed for use with the Yamaha RX-V2090 AV Receiver, which is the unit we tested it with. However, the outputs from the processor (RCA jacks on the back) can be fed to five separate power amplifiers (and a powered subwoofer) if you wish, although this would complicate the integration of standard Pro Logic. The DDP-1 has volume controls (through the pushbuttons on the front panel) for the overall signal, called Output Trim, in 0.5 dB steps from -9 dB to 0 dB, and the rear channels - left surround and right surround, in 1 dB steps from -6 dB to +6 dB. Since the overall level trim is limited to 9 dB, this might not be enough to lower the volume sufficiently on some power amplifiers, depending on their sensitivity and power output. So, going the DDP-1 direct to power amps route would necessitate the consideration of power amps with level controls of their own. Of course, this was not an issue with the RX-V2090, since it has the appropriate inputs (five channel discrete), and its own level control. A Mitsubishi AC-3 laserdisc player (has AC-3 RF output) and M&K speakers (including sub) rounded out the complete system. As AC-3 matures, I am sure we will see more and more processors and receivers with "pass through" features that allow connections to several units. Otherwise, somebody out there is going to start selling a heck of a lot of source/output switching boxes.
OK, how does AC-3 sound? Well, in a word, fabulous. "True Lies" took center stage, and to hear the thunder on a new plateau was breathtaking. Machine gun fire from all four corners, vehicles moving from right rear - sweeping to the front right - then left . . . I have to say that I am hooked, and for good. Pro Logic is great, but the move to AC-3 is like going from black and white TV to color. No more diffuse background to give you the "sense" of ambience. With AC-3, YOU ARE SURROUNDED! No ifs ands or buts. I am reminded of the old days when the original "Lawrence of Arabia", and "How the West Was Won" played at the theaters (cough, cough . . Yup, I'm a 50 year old geezer). Real, discrete multichannel sound. Now we can have it at home!
It is difficult to compare the same movie in Pro Logic because the mix is different. But, we did not notice any harshness, nor any sense of something missing (AC-3 uses perceptual coding, where only the sounds that the human brain are likely to respond to - as determined through psychoacoustical testing - are included) that has been suggested might be the case with the AC-3 data reduction scheme. In fact, the overall effect is much, much better (in our opinion) and more enjoyable than Pro Logic. Of course, we were using the DDP-1 with top of the line associated equipment. Harshness can come from numerous sources: underpowered amps, speakers, even the laserdisc soundtrack itself. Three separate 20 bit DACs are used in the DDP-1 to process the signal after it has been demodulated and decoded. The mains, center, and rear can be configured for full spectrum sound, or set for high pass (crossover 90 Hz, 12 dB per octave slope) - signals below 90 Hz (crossover 90 Hz, 24 dB per octave slope) being sent to the subwoofer. The center and rear signals below 90 Hz, as well as the LFE (low frequency effects channel going to the subwoofer) can be routed to the mains, if they are large speakers and you don't have a subwoofer. The LFE channel level output can be trimmed from -20 dB to 0 dB in 1 dB steps. We found that directing all the low frequency sounds to one subwoofer resulted in a rather boomy low end, probably just too much for the sub when combined with the LFE channel output itself. (Uh oh, here comes the fork lift with a couple more subwoofers.) The dynamic range can be adjusted if your amplifiers and/or speakers (or ears!) can't take the heat. The rear channel delay is variable from 0ms to 15ms in 1ms steps. The center channel signal can be delayed also, up to 5ms in 1ms steps, and this is quite interesting. Assuming that you sit in the middle, the center channel sound reaches you faster than the mains, thus the adjustable center channel delay. However, there is no individual level adjustment for the center with respect to the mains, a feature we feel should have been there, along with individual adjustment for left/right mains (since the left/right rear levels are individually adjustable). One can adjust them on the receiver, but such features would have made the DDP-1 more useful with other configurations. A pink noise generator (all frequencies mixed at equal energy) is built into the DDP-1 for balancing the sound levels.
The front panel has three rectangular push buttons, for "Mode", "Menu" and "Parameter", along with a LCD for indicating what is being adjusted (the input status is also indicated here). Yamaha has shoved a lot into what these three buttons do, and put the rest of the money into the processor. Good planning, and a fine product results. The DDP-1 can be used with the 44.1 kHz digital output from a CD transport, but this is a test mode function for service personnel, not for us (at least for now). If you can't wait until all the manufacturers have AC-3 receivers on the shelf to choose from, or if you like the full separates route (I kind of like the idea of handling the RF demodulation in a different chassis from the amps), you can't go wrong with buying one of these units, even though it might take some fiddling around to integrate it into your system. If you have a Yamaha RX-V2090 receiver, then an AC-3 laserdisc player and the DDP-1 are a must, and I mean MUST! Highly recommended.
John E. Johnson, Jr.
© Copyright 1995, 1996, 1997 Secrets of Home Theater & High Fidelity
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