Denon AVR-4800 THX Ultra digital surround receiver
The AVR-4800 is the lightest, smallest, and least expensive of three A/V surround receiver introduced by Denon in the past 18 months. (The others are the $2800, 5-channel AVR-5700 and the $3800 7-channel AVR-5800.) Its 5-channel surround A/V chassis includes a full array of home-theater features. To manage all functions, it sports a dazzling number of rear-panel connectors: 70 RCA jacks, 14 loudspeaker cable terminals, 10 S-video connectors, 6 optical connectors, 3 auxiliary AC power jacks, and an IEC jack for the AC mains—a veritable Rosetta Stone for home theater.
Digital Signal Processing: The AVR-4800's main job is decoding Dolby Pro Logic, Dolby Digital, and DTS. The resulting multichannel signal is then post-processed by THX 5.1 and THX Surround EX 6.1-channel circuitry. What is THX Surround EX 6.1? Standard 5.1 surround offers no rear center channel to match the front center speaker, making it difficult to make perceived soundsources travel from back to front. To create a more convincing illusion of rear-fill surround, a discrete rear-center signal is needed, like that of Surround EX 6.1 THX. George Lucas supported this concept by demanding that 4600 movie theaters worldwide install Surround EX in order to show Star Wars: Episode I—The Phantom Menace.
Soundtracks encoded with Surround EX are completely back-compatible with Dolby 5.1 systems. THX Surround EX 6.1 sources are automatically detected using the data flag in the 5.1 soundtrack's metadata when the setup menu for THX Surround EX is set to Automatic. The AVR-4800 is also DTS ES–compatible, providing an additional surround rear channel when reproducing DTS ES–encoded DVD-Video discs such as The Haunting.
Surround Modes: The AVR-4800 also offers DSP simulations of various concert and film venues. The Widescreen 7.1 DSP mode can create a 360° panoramic soundfield from any stereo, matrix, or discrete 5.1 program source, using seven speakers (two front, one center, two side, and two rear) and a subwoofer. The AVR-4800's Personal Memory Plus function recalls the preferred surround mode, speaker configurations and levels, and surround parameter settings and input mode, all keyed to the selected input source. For example, if the DVD input is selected, Personal Memory Plus engages the processor to decode Dolby or DTS, with or without THX, and selects the proper configuration of side and rear surround speakers.
Denon's Dynamic Discrete Surround Circuitry (DDSC) manages surround decoding, post-processing, and seven adjustable ambience modes. These functions are executed by two Analog Devices SHARC (Super Harvard ARchitecture Computer) DSP chips working in tandem, each rated at 50 million instructions per second (MIPS) with a peak throughput of 120 million floating-point instructions per second (MFLOPS). The first SHARC chip performs the Dolby Digital and DTS surround decoding, the second the THX post-processing, THX Surround EX decoding, bass management, and seven other DSP environment simulations, all in the digital domain. These DSP simulation modes are fully adjustable in terms of effect levels and soundfield size. The SHARC chips use floating-point arithmetic, which Denon claims yields more dynamic-range capability than fixed-point devices.
Denon's DDSC-D uses a separate, parallel stereo analog pathway selectable by pressing the Direct button on the front panel or remote. Denon claims that other manufacturers often digitize all incoming analog signals, even for simple two-channel music applications. The Direct option preserves analog signal integrity for high-resolution signals like analog LP or HDCD-encoded CDs.
In addition to the SHARC DSP units, the AVR-4800's digital interface receiver accepts PCM digital audio of up to 24-bit word lengths and 96kHz sampling frequency, from Chesky and Classic Records 24/96 audiophile DVDs. Full 24/96 D/A converters are available on all eight audio channels (unless Direct is selected). When the DSP section is used, analog inputs are converted to digital via 20-bit oversampling A/D converters.
Audio Amplification; The AVR-4800 has extra surround-sound speaker output terminals to allows the owner to mount a pair of bipolar surround speakers high on the side walls near the listening position to generate a broad, diffuse soundfield, best for the reproduction of a soundtrack's surround signals. Alternatively, the owner can place rear-mounted, forward-facing, direct-radiating speakers in the rear corners of the room. This produces a more natural surround impression with discrete multichannel music.
Although the AVR-4800 has seven pairs of speaker output terminals, it can drive only five of those channels at one time. To be able to deliver 7.1-channel surround sound, you have to hook up an additional outboard two-channel amplifier to drive the side surround and rear speakers. I used a Denon POA-5200 THX Ultra stereo amplifier (120Wpc into 8 ohms) to drive the Revel Salons, my front speakers, and programmed the AVR-4800 to control levels, delays, and equalization to the POA-5200, while using the AVR-4800's five amps to drive the center speaker and the pairs of side and rear surrounds.
Bass management is a crucial element in good surround sound. The Denon AVR-4800's bass-management circuitry is certified THX Ultra, and so includes Lucasfilm's required 12dB/24dB Linkwitz-Riley electronic crossover set at 80Hz to blend the main speakers with the subwoofer. The setup routine allows one to set up the bass-management system to specify the frequency characteristics of the system's speakers and to provide protection for the subwoofer against sudden transients.
The video switching path offers wide bandwidth (27MHz, –3dB) for digital TV and/or progressive compatibility found in HDTV signals. The DVD player input is also provided with component input capability. In order to preserve the video signal integrity, two types of monitor outputs (both composite and S-video) are provided: only Monitor 1 features onscreen display, to let the user set up the system. Later, when the user is familiar with the system configuration, he/she can reconnect to the Monitor 2 outputs, for the purest video passthrough quality.
Internal Construction: The AVR-4800 meets THX Ultra certification standards, which require stable operation at high volume levels into a wide range of loudspeaker impedances. This includes meeting its published power and distortion ratings as well as being able to operate up to clipping with all five channels, each driving separate 3.2 ohm loads.
The power-amp block features an internal heatsink tunnel with two cooling fans. A microprocessor balances output-transistor heat and fan noise to keep the cooling system quiet during low-volume passages. The front, venturi-mounted fan is activated first; if the internal heat continues to rise, the rear-panel exhaust fan then kicks in. On one side of the chassis sits a single, large toroidal power transformer and high-current, low-ESR electrolytic power-supply capacitors.
Internal construction and wiring are cost-effective, with many point-to-point connections. Although the AVR-4800's build standard differs from the cost-no-object, bulletproof construction found in high-end amplifiers, the internal component quality is satisfactory and the chassis construction durable. A good protection circuit shuts down the receiver in the case of a short in a single speaker lead.
Old Dog, New Tricks
Reviewing the AVR-4800 was a real eye-opener, especially for a dyed-in-the-wool two-channel audiophile like me. For starters, I had to wrap my mind around the fact that the AVR-4800's main installation is not just wired, but programmed. Setup involves a lot more than "hooking up the stereo." Configuration of sources, processing modes, and assignment of speaker channels must be programmed using an onscreen setup menu so all those processing modes can be selected automatically—a godsend, because I still can't recall them. Whether one plays a movie in standard 5.1 surround Dolby, DTS (Saving Private Ryan), or in THX 6.1-EX (The Bone Collector, it's best to toggle the remote's Input switch to Auto and let the AVR-4800 choose.