Sony SDP-EP9ES
A Dolby Digital decoder that arrived before DVD did, and made itself the quiet center of a serious home theater.
Overview
The SDP-EP9ES is a standalone Dolby Digital surround processor - not a receiver, not an A/V preamp with video switching. It takes a digital bitstream and turns it into six channels of analog. It sold for $750. That sounds like a lot for a decoder, but laserdiscs with Dolby Digital soundtracks got to market before DVD players did, and laserdisc players can't hand off an AC-3 bitstream directly. They carry it as a radio-frequency signal that has to be demodulated first. Sony built the demodulator in. Audio (July 1997, p.46) laid out the problem plainly - early Dolby Digital adaptors either had an RF input and no bitstream inputs, or bitstream inputs and no RF demodulator, leaving laserdisc owners with one eye on DVD stuck. The SDP-EP9ES has both: an AC-3 RF input plus four bitstream inputs (three Toslink optical, one coax RCA).
That input set is the whole argument for the thing. It can decode Dolby Digital from a laserdisc's RF output and from a DVD player's bitstream, and it can run Dolby Pro Logic on matrix-encoded stereo digital signals besides. It can't decode analog surround. It will pass an analog surround signal through, but the decoding has to happen elsewhere. So the intended install is either between an A/V preamp and the power amps, or into a Dolby Digital-ready receiver or integrated amp that has the necessary inputs. When it's off, or set to its "Bypass" mode, it's transparent to the analog path and the rest of the system handles volume and source selection. When it's on and one of the five digital inputs is selected, it becomes the audio controller, with its own volume, tone, and surround adjustments. Video routing stays with the other components. This box neither generates nor handles video, so its setup menus appear only on its own display panel and never on your TV.
The front panel carries a volume control, two "Digital Processing Control" knobs (one to pick a menu, the other to step through it), four "Digital Cinema Sound" pads, and an input selector with buttons for the five digital inputs plus Bypass. A 28-button remote does the same work, and owners report it often means navigating nested menus and submenus. The "Set Up" menus are where you tell the processor what speakers you actually have: presence or absence of center and surround speakers and subwoofers, large or small for mains, center, and surrounds, rear or side placement of the surrounds, and the distances from each speaker to the listening position. From those distances it sets the channel delays automatically. Distances are entered in 0.1-meter steps by default or in 1-foot steps, with mains allowed anywhere from 1 to 12 meters, the center up to 1.5 meters closer than the mains, and the surrounds up to 4.5 meters closer.
Speaker size is what lets it redirect bass. The default crossover for that redirection is 120 Hz, adjustable from 60 to 200 Hz in six steps, per channel. The tone controls go further than most. In "Expand" mode the bass and treble are quasi-parametric, ±10 dB in 1-dB steps, with 21-step turnover adjustment - 99 to 992 Hz on the bass, 1 to 8.6 kHz on the treble - and separately for main, center, and surround. The "Basic" menu handles speaker levels, dynamic-range compression for late-night listening, plain bass and treble, subwoofer level, muting, and display brightness in 1% steps. A "Memory Clear" restores factory settings after asking for confirmation.
The Digital Cinema Sound modes are the period-flavored part: "Enhanced Surround," "Large Theater," three "Cinema Studio" modes that simulate two theaters and the scoring stage at Sony Studios, two "Virtual Rear" modes that modify the apparent number and placement of surround speakers, two "Virtual Enhanced" modes that synthesize surrounds when none are used, plus "Large Hall" for music and "Live House" for synthesizing surround from a mono source. Effect level is adjustable from the remote. The digital inputs lock onto 48, 44.1, or 32 kHz, not 96 kHz. The decoder recognizes the seven variants of Dolby Digital encoding (1/0 through 3/2), and it automatically distinguishes stereo, matrixed Dolby Surround, and AC-3. Outputs are a Toslink jack for driving a digital recorder plus analog jacks for all 5.1 channels, with dual parallel-connected jacks for center and LFE. All the RCA jacks are gold-plated, and the Toslink jacks ship with protective plugs.
The measurements are where this unit does its best work. Audio (July 1997, p.48) was blunt that the DACs in several surround processors and A/V receivers it had recently tested performed below par, and called it idiocy to buy a good CD or laserdisc player for its converters and then hand the signal to an external box with worse ones. The SDP-EP9ES's converters came out very good indeed. Frequency response was flat to about 10 kHz and down a mere 0.1 dB at 20 kHz, with no treble ripples even on an expanded scale, which the reviewer read as evidence of an excellent digital filter. THD + N measured −86.8 dBFS (0.0046%) at 0 dBFS, dropping below −92 dBFS at −10 dBFS and below −93 dBFS at −30 dBFS. Linearity error barely exceeded 1 dB at −90 dBFS with undithered signals and stayed under 0.25 dB worst-case with dithered recordings between −70 and −100 dBFS. Channel balance was excellent and output impedance admirably low. Volume was set at −16 for the standard 2-volt output, but the unit can deliver more than 9 volts before clipping, far more than needed to drive a power amp. Clipping occurs in the analog output stage, as it should.
On the AC-3 RF side, measured with a Dolby Labs surround laserdisc, Audio found frequency response identical to the D/A converter's and distortion readings higher for the RF input than for the converter section, possibly slightly higher noise rather than distortion. Main-channel balance in AC-3 RF mode held within ±0.14 dB worst case, channel separation at 1 kHz ran mostly 100 to 115 dB, and worst-case leakage was about −75 dB. The LFE channel measured higher distortion at 30 Hz, which the reviewer waved off given that channel's nearly 10 dB higher output. In listening, the same review compared a DVD player's analog outputs through a Dolby Pro Logic decoder against the Dolby Digital track decoded by the Sony. It found the Dolby Digital path decisively better for movies, since the stereo surround and LFE bass don't survive the analog mixdown, and noticeably more detailed and transparent on music CDs as well.
One caveat about the reception record: the SDP-EP9ES was heavily advertised, and some of the praise floating around is marketing copy rather than independent testing. HiFi-Stereo (December 1997, p.33) ran a Sony advertisement that collected blurbs from Stereophile Guide to Home Theater, Hi-Fi News & Record Review, Hi-Fi Choice, and Home Entertainment - "approaches the state-of-the-art," "a truly magnificent example of digital engineering," and so on. Those are quotes in an ad, not a review. The independent bench work is the Audio profile.
Physical footprint: 17 inches wide, 3¾ inches high, 11⅛ inches deep, 14.3 pounds. It's a half-rack-width-ish box that sits quietly in a stack and does one job. Collectors chasing one today should expect the usual for late-'90s digital gear. The format it was built around has moved on, and the value is in the RF demodulator and the good converter section rather than in the surround modes. The Cinema Studio and Virtual Rear modes are period curiosities.
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