Sony D-555
The Discman that carried a full rack of digital signal processing into a car, a backpack, and a pair of headphones — and charged $450 for the privilege.
Overview
The D-555 is the portable CD player Sony built for people who refused to accept that "portable" meant "compromised." Where most Discmans of the era were stripped-down transports with a headphone jack, the D-555 arrived with a five-band digital graphic equalizer, digital surround, bass boost, and a digital dynamic-range compressor — all of it processed in the digital domain before the signal ever reached the converter. That processing architecture is the whole point of the machine, and it's why the D-555 still gets pulled out of drawers decades later.
The spec sheet reads like a home deck's. Frequency response is quoted at 20 Hz to 20 kHz, ±1.0 dB, with a signal-to-noise ratio greater than 90 dB. Line output is 0.7 V, there's an optical digital output rated -21 to -15 dBm, and the headphone jack delivers 9 mW into 32 ohms. The chassis measures 5 inches wide by 15/16 inch high by 5 11/16 inches deep and weighs approximately 1.5 lbs. At $450 when new, it sat at the top of the Discman range — a serious premium over the bread-and-butter models, and Sony priced it accordingly.
What separates the D-555 from a garden-variety portable is how much of Sony's home-unit feature set made the trip. Track access works by audible scanning, direct track number, or index. Repeat modes cover a single track, the full disc, an A-B segment, shuffle, and programmed play, and the machine will store up to 22 selections in any order. Power comes from a built-in rechargeable battery, the supplied AC adaptor, or an optional car-battery cord. That last option matters more than it sounds, because the D-555's DSP was explicitly designed around the car — more on that below.
The control layout is where Sony's engineers earned their keep. Rather than bolting on a knob per function, they assigned multiple duties to a handful of keys. A "Key Mode" button cycles the two search buttons through track-to-track advance, fast audible search, and index advance. A "Play Mode" button steps through intro scan, the five repeat modes, and back to normal play. "Enter/Remain" toggles the display between remaining time on the current track and remaining time on the whole disc, and doubles as the store key during programming. A Hold switch on the front locks everything so the player can be carried without random button presses. The result is a lot of capability without a cluttered face — a genuinely thoughtful piece of industrial design for a portable.
The display is split across two windows: the front panel shows track number and elapsed time, while a secondary window on the top surface shows the DSP settings. That top display is what you watch when you're dialing in the equalizer, and it's also what runs the player's demonstration mode — press EQ, "+," and "-" together and the D-555 walks through each effect for roughly ten seconds apiece (twenty for the equalizer) so you can hear what each one does to the music.
The DSP suite itself is the headline. There's a digitally based five-band graphic equalizer, a surround-sound circuit, a bass-boost circuit, and a dynamic controller (compressor). Because all of this happens in the digital domain, the equalization, surround, bass boost, and compression affect the signal at the optical output as well as the analog jacks — not just the headphone feed. A headphone jack sits on the right side panel; a remote jack and the optical digital output are on the left.
Audio (February 1991, p.40) put the D-555 head-to-head against the Denon DCP-100 and NEC's TurboGrafx-16 CD player, and framed the contest neatly: the Sony brought digital equalization, compression, surround, and bass boost, while the Denon leaned on advanced D/A processing and simplicity. In the listening tests, the reviewer ranked the Denon first for outright sound quality, the Sony a close second, and the NEC a distant third — but handed the Sony the features crown without argument. The same review measured the D-555's frequency response with a slight treble rise of no more than about 0.5 dB, and found THD+N at 1 kHz of slightly more than 0.03%, with an A-weighted signal-to-noise ratio of nearly 94 dB. That's a strong showing for a portable of the period, and the reviewer's summary — best sound to Denon, best features to Sony — is about as fair a verdict as the machine ever got.
The feature that impressed that reviewer most in real-world use was the digital compressor. Driving with the D-555, he found he could listen to classical music without constantly riding the volume control as dynamics swung — exactly the problem the compressor was built to solve. He was candid that the effect is less useful for rock and pop, where it may barely be audible. The surround circuit, meanwhile, surprised him through headphones: he expected surround to fall flat without front and rear speakers and found it genuinely effective on good stereo material. The equalizer got a practical workout too — using Sony's own owner's-manual presets for car listening (rock, vocals, background music, '50s sound, and a "natural sound" setting), he confirmed the recommended curve improved tonal quality on the road, though he still nudged the 250 Hz band down a touch to taste.
That's the D-555 in a nutshell: a portable that expects you to actually use its processing, and rewards the effort. It is not a purist's machine. If what you want is the cleanest possible straight wire with gain in a portable, the period review suggests the Denon was the better pick, and the D-555's own DSP is the reason — every effect you engage is a choice to color the sound. But as a piece of engineering, the ambition is hard not to admire. Sony took the feature set of a home CD player, put it in a 1.5-pound box, and made the controls make sense.
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