Philips IS-5021
A tabletop "Sound Enhancer" with 20-bit conversion, sample-rate conversion, and a grab-bag of noise processing in one box, at about half the price of its rackmount sibling.
Overview
The IS-5021 is the consumer half of a two-model family. Philips Key Modules built the Sound Enhancer in two versions: the IS-5022, a single-rackspace pro unit that ran $2,400, and the IS-5021, a tabletop package at $1,500. Both share the same core - 20-bit A/D and D/A converters, sample-rate conversion, and a suite of noise and dynamics processing. The 5021 strips the connectivity down to what a home studio actually needs. Electronic Musician (undated review, p.1) put the pair plainly: recordists who don't need AES/EBU I/O and balanced analog I/O "may be better off with the consumer-oriented IS 5021 instead of the far more expensive IS 5022."
Both units accept signals sampled at any frequency between 15 and 50 kHz and convert them to 44.1 or 48 kHz. That was handy when DAT decks, samplers, and early hard-disk rigs all seemed to run at different rates. The 5021 has analog I/O and S/PDIF digital I/O on RCA connectors. The 5022 adds AES/EBU and balanced XLR for the pro rack. That single difference is the whole reason the 5021 exists at its price.
The converters are the headline. Twenty-bit A/D and D/A in a $1,500 tabletop box was serious specification for the mid-1990s, and Philips leaned on it hard. A jitter-removal feature is included for transferring DAT recordings that have the problem. Electronic Musician noted that Philips claimed the circuit "automatically removes any jitter from a digital input." The reviewer admitted he could not detect audible jitter in his own signals, so he couldn't verify the claim. That makes it a manufacturer promise, not a demonstrated result.
Processing is where the box gets busy. Quantization Noise Imaging improves 16-bit signals by adding dither to push noise outside the audio range. A scratch suppressor/declicker and an adjustable lowpass filter (6 to 16 kHz) round out the noise-reduction side. There's also compression, expansion, ±12% pitch variation that does not affect the output sample rate, fade in/out, soundstage (spatial) enhancement, and bass and treble shelving filters. Stereo balance and level controls are supplied, and a pair of 26-segment LED meters indicate levels on both versions.
Audio (August 1996, p.63) was impressed with the tone controls, finding the bass and treble action "precise and repeatable" and the resulting tonal changes more to the reviewer's liking than is typical. The same review praised the "Spatial" feature for adding spread to narrow stereo recordings. The dynamics side got a cooler reception. Electronic Musician criticized it for offering only ten fixed ratios, which the reviewer called "disappointing" for the limited control it gave the user.
One feature the 5021 does not have: the tabletop version does not remove the copy-protection bit from SCMS digital signals. The 5022 does. If transferring copy-protected DAT material is the job, the cheaper box won't do it. Electronic Musician flagged this as the key functional gap between the two.
Both units are powered by external DC supplies. A missing wall-wart is a real annoyance decades later, and it can quietly kill a secondhand purchase. The 5021's tabletop form factor means it sits on a desk rather than bolting into a rack, which suits the home recordist it was aimed at.
The verdict from the period was measured. Electronic Musician's reviewer said he would mix a record through the 5022 "without reservation" and called it a quality product, but would not insist on having one in his own project room. He wanted better processing with more extensive control before calling it a must-buy. For the 5021 specifically, the same reviewer judged it "a good purchase for many semipro home studio owners" given its pro-audio-quality converters at a reasonable price.
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