ã 2001 by Eddie Ciletti
For those troubled by the sterility of digital, vintage gear offers color options galore, but along with them is the "baggage" of maintenance. In addition, gear designed thirty to fifty years ago didn't need to be as quiet. As sexy as analog tape is, "oxide" and recorder noise conspired to hide other noises... Yes, digital changed all that, but the response by "boutique" manufacturers has more than filled the sonic void.
In case you haven't noticed, I like reviewing gear from small independent audio companies. The products I've scrutinized to date are generally over-built by people who take their audio seriously, as you do. Don't believe me? Drop an e-mail or call on the phone. Chances are you'll find the designers are accessible and passionate, though busy. Often hand assembled, their gear is more likley to stand the test of time just like the vintage gear that is so hotly desired.
I am not one who believes digital technology is bad, but it forced us all — enthusiasts and uber-geeks alike — to take a crash course in the study of "ancient" equipment. That's why my reviews tend toward the educational, because I am still learning about what sounds good and what makes good sound. Sharing that knowledge transcends the negative aspects of gear lust — talent and execution must come first — but knowing how to apply the right piece of gear to an audio challenge comes from study and experimentation.
With that in mind, Crane Song’s HEDD 192 along with the Great River MP-2NV both provide the kind of "sonic airbag protection" associated with vintage using two radically different approaches. HEDD is a stereo converter with analog emulation and the MP-2NV is a stereo mic preamp a la Neve. While it is not customary to evaluate two products from two manufacturers within one review, the coincidence of theme and timing was just too perfect. Each approach proves that there is more than one way to skin the proverbial cat, but in this case, no animals were harmed in the testing process.
As the name suggests, HEDD 192 will accommodate sample rates up to 192 kHz and 24-bits. As "just" a converter, this second generation version of HEDD — a Harmonically Enhanced Digital Device — includes dither that is exclusively Crane Song’s. The product currently ships with socketed 96kHz converter boards; the upgrade path is waiting for acceptable parts and communications standards. The DSP includes three emulation controls labeled TRIODE, PENTODE and TAPE with a common Bypass switch. The processing can be applied at any time to either the analog or the digital signal path. Just rotate the knobs clockwise and enjoy.
Of the three controls, Triode generates the type of even-order (octave) harmonics associated with single-ended vacuum tube circuits. This effect can be masked by harmonically-rich content so, depending on the signal being applied, it may not seem to be the most obvious at first. Darker sounds benefit most from this process. From left to right, each control — TRIODE, PENTODE and TAPE — becomes progressively more responsive. Once familiar with their affect, you'll be twisting a little of each for infinite variations.
For the first test, the output of my Soundscape workstation was routed through HEDD to "warm up" a mix-in-progress. Visitors have been quite impressed with the before and after demo — there's nothing subtle about it — turn the TAPE knob clockwise and the track gets larger without increasing "overs," without sounding compressed, simultaneously adding richness to the bottom and mids.
I also used HEDD to emulate an AMPEG B-15 bass amp by routing an electric bass track through it, crankin’ the Pentode knob to increase the "spectral content." By adding a sweet bit o’distortion, a nice round Bass Guitar became more bull-ish, capable of sitting in the mix through verse and chorus without getting lost in the sauce. That’s deep, with or without the pun.
The emulation makes astounding visuals starting with Figure-1a, a family of Sine waves from clean to mean. In Figure-1b, the NTI Minilyzer was used to view the harmonic content via 3rd Octave display. The arrow points to1kHz (the fundamental), to the immediate right is the 2nd harmonic — 2kHz — one octave above. Figure-1c points out the 3rd harmonic. What is amazing about HEDD 192 is that all of the distortions are so controlled — no hard-clipping, only phat, although it is possible to go overboard, it does sound alot like analog tape.
Figure-1a: From left to right, three sine waves depict what controlled distortion looks like as delivered by HEDD 192.
Figure-1b: The 3rd octave display of the NTI MiniLyzer shows how Triode mode generates even order harmonics. In this case, 2kHz is one octave above the fundamental.
Figure-1c: Using Pentode and Tape mode together generates plenty of odd harmonics, the third and fifth being 3kHz and 5kHz, respectively.
Inspired by the ever-colorful Fletcher of Boston-based Mercenary Audio, the Great River MP-2NV is a stereo mic preamp based on the Neve 1073 module. Like a real Neve mic preamp, the MP-2NV has a rotary switch for coarse gain and the equivalent of a fader to trim the gain. (The gain switch actually dials in various combinations of amplifier stages, gain and input transformer attenuation.)
Input Gain for the MP-2NV is in 5-dB steps, Output Gain is continuously variable from –20-dB through unity to +10-dB plus metering for both stages. As such, it is possible to purposely run the preamp hotter than the output amp, or vice versa. I found this extremely helpful when recording drums using a single pair of Marshall MXL-2003 large-diaphragm condenser mics (in X-Y about 3-feet off the ground and about 3-feet in front of the kit). With the "Fader" set to unity gain I allowed 4~6dB of headroom, easily readable via HEDD’s metering, which is in 1dB steps all the way down to –10dB FS.
THE ANIMAL RUMBLES
Drummers being the animals they can be, repeated "overs" during moments of excitement can be tamed by turning down the output gain and cranking up the input gain. Again allowing 4~6dB of headroom at the converter, the new settings eliminated all "overs" and, with drums at least, there was no sign of undesirable distortion. How cool is that? Of course you also can be "nice" to the MP-2NV. On vocals and cello I found it full-bodied — round on the bottom and crystal clear on top.
It is common to see Neve gear being abused — I always felt sorry for the mechanical VU meters because people "buried" the needles. Maximum output level is +27dBm, easliy 10-dB more headroom than any mass-produced IC opamp-based preamp or mixer. At the other end of the spectrum, the Great River MP-2NV has 15- to 20-dB less noise than its vintage ancestor. By consolidating all the plug-in cards onto one circuit board, and using low-noise components throughout and a very quiet power supply, the signal-to-noise ratio is in excess of 105dB at the 30-dB gain setting and 96-dB at 60-dB gain, unweighted.
When driven hard, Class-A Neve circuits — and the transformers that interface them — react to transients like peak limiters. There is even a dynamic recovery time, although that's not easy to show in print. You can see what happens to "static" sine waves in Figure-2a. Note that each stage behaves similarly, clipping only half the wave first. Assuming your signal "goes there" only momentarily, the effect is must less obvious than with any IC opamp, where symmetrical clipping is "instant nasty." In reality, the color starts before any obvious clipping occurs. In Figure-2b, the third octave display of the NTI MiniLyzer indicates not only the second harmonic, but a cluster of harmonics starting with the third.
Figure-2a: From left to right, a "clean" sine wave with distortion below .01%. Next, 1% distortion of the Direct Input FET is barely visible on the bottom of the wave. At 2%, the bottom edge of the Preamp Stage is clearly flattened, while the top is just beginning to get leveled. Finally, the output amp is taken to 5% distortion and still doesn’t show any signs of clipping the positive excursion of the wave.
Figure-2b: A 3rd octave analyzer shows the spectral content of the MP-2NV output amp driven to 2% distortion. This is not an easy thing to do as the maximum output level is +27dBm!
Three other features make the MP-2NV an asset starting with the Direct Input. A traditional mic pre / active DI connects the instrument directly to the first amplifier, bypassing the input transformer. Fletcher insisted on using the input transformer for additional color and, as unconventional as that might be, Dan Kennedy’s clever and effective solution was to put a FET impedance converter in front of it for Hi-Z happiness — the perfect match for passive bass and guitar.
My Univox P-Bass copy sounded surprisingly round through the direct input. It was neither clangy nor unnecessarily subsonic. While there is no metering to indicate FET overload, doing so is pretty obvious. I simply turned the level control down on the bass. Again, manipulating the input and output gain controls can massage the tone range, which is enhanced by good technique and a consistent touch. (I’m still working on that.)
To further trick out the MP-2NV, the input transformer has multiple windings, just like the Neve modules, only now the input impedance switch — which provides the correct impedance range for 50- to 200-ohm microphones — is on the front panel. This is cool if you have ribbon mics plus the "50-ohm" setting loads the FET for a different sound. (The input impedance range is actually 300- and 1200-ohms.)
Output termination rounds out the options. Many people, accidentally or not, run Neve modules un-terminated, the resulting sound can be brighter due to transformer ringing. (See Figure-3.) By placing the option on the front panel, users can run either way and not have to futz with resistors or ever have to go to the rear panel for anything other than Input, Output, Insert and Power connections. This also changes the overload characteristic of the output amp.
Figure-3: The effect of termination (and lack of same) on a 1-kHz square wave. The un-terminated "spike" indicates transformer ringing that produces a 7dB boost at 50kHz.
Figure-4: How Digitization Affects Square Waves
The rise time (vertical excursion) represents high frequency response while Time (lower frequencies) are represented horizontally. The effect of sample rate on bandwidth and filtering is easily seen when a square wave runs through the conversion process. Note how doubling the sample rate reduces the ringing caused by anti aliasing filters. Analog Tape Emulation is more difficult to capture in a single image, but at the bottom, the high frequencies have been slowed down a bit while helping the mids and lows…
As mentioned, recording was done at 88.2kHz, via Alesis Masterlink, this sample rate minimized the math for future comparison at 44.1kHz.
What you never see is the effect digitizing has on square waves, Figure-4 does just that via HEDD 192. Notice how much more sedate the "ringing" is at higher sampling rates. Also see how Tape Emulation affects the wave. Again, like the MP-2NV, saturation is a dynamic process that can not be depicted in print. Tape saturates at high frequencies because of the record EQ boost and at low frequencies due to head limitations. That’s two different idiosyncrasies plus low frequency head bumps, a complex bit of DSP.
All tests were monitored on modified Fostex NF-1A powered monitors as well as the Yamaha NS-10m. Gear comparisons via Studio Technologies STUDIO COMM. All sources were adjusted to within 0.01dB through the Studio Comm using the NTI Minilyzer.
Square waves make it easy to see in one "snapshot" how both high and low frequencies are affected. A square wave consists of all odd harmonics — essentially sine waves ripped through a fuzzbox, clipped symmetrically top and bottom. Assymetrical clipping generates even harmonics.
HEDD 192 is Crane Song’s second-generation stereo digital converter, adding higher sample rates as well as tape emulation (the original version featured only vacuum tube emulation). Next to an LA-2A, HEDD is the most simple digital signal processor you’ll ever use.
While there are plenty of Neve variations — from repackaged modules to new — the MP-2NV is a completely new product from Great River whose two other preamps are radically different designs. Pick your fave flave. Time travel is not yet possible, but the MP-2NV has features that enhance what was already a good thing, almost like being back in the sixties. There is plenty of gain and surprisingly low noise for delicate acoustic work even when using a ribbon mic.
Both the MP-2NV and HEDD 192 provide their own brand of sonic airbag protection for drums and other transient instruments without sacrficing detail when used "under normal conditions." Combined, these two products make the recording process more fun by providing a remarkable level of sonic versatility, two sonic crayons that can paint a whole rainbow. Sessions will be more fun, life will be easier and each will be providing reliable service for years to come.
Eddie finally wired his garage for sound and video. What’s next, a surfboard
and some hot wax?
Most design engineers strive to design the most accurate and transparent circuitry possible. In a way, digitized audio is the result of such pursuits, the reactions to same forced many designers to reinvestigate vintage analog technology. Was it really better? Increasing the sample rate and bit depth alone will not make digital sound more like analog. It’s analog’s idiosyncrasies that everyone waxes romantically about, the intense study and ultimate emulation of which is essential to the progress of digital audio technology.
Both Dave Hill at Crane Song (in Superior Wisconsin) and Dan Kennedy at Great River (here in the Twin Cities) realized that recording engineers need a full-spectrum sonic palette. Sometimes this means going against their instincts. Yes, there are times when transparent-clean is the best and only choice. Other times a little grunge helps bring a more aggressive "street" feel to studio tracks that can sometimes be too sterile, especially now that analog tape has become more a piece of outboard than a standard part of the recording process.
Fletcher commented that many input and output transformers were auditioned before landing on the combination in the MP-2NV. Prototypes were passed between Massachusetts and Minnesota before commiting to the final set, chosen because they were clearer, deeper and "punchier" than those found in the original 1073 design.
Just as television and print exaggerate the warmth of flesh-tones (think
distressed furniture, acid-washed jeans and a broken-in pair of sneakers);
analog’s artifacts are used to saturate sonic colors to reproduce sounds
more vivid than reality.
The Great River MP-2NV "Mercenary Edition" stereo microphone preamplifier
Inputs: Transformer-Balanced Microphone via rear-panel XLR connectors and instrument inputs via front quarter inch jacks.
Input Impedance: 300 and 1200 ohms (to accommodate 50- and 200-ohm mics), greater than 1-megohm (instrument). ß a guess)
Insert: Unbalanced TRS in between preamp and output amplifiers for outboard such as compression and equalizers.
Outputs: 600-ohm Transformer-Balanced line level via rear-panel XLR connectors. Maximum Output level +27dBm, terminated.
Controls: Input Impedance switch, output termination switch, Input Gain rotary switch, Output Level rotary pot, Polarity Reverse, Phantom Power.
Price: 2,499.00 list.
The Crane Song HEDD 192
On the Rear Panel: Balanced Analog Inputs and Outputs via XLR connectors. AES and SPDIF I/O via XLR and RCA connectors, respectively. Word Clock in and out. Power.
Controls: Sample Rate, Bit Depth (also inserts DSP in the correct signal path), AES / SPDIF, Word (internal and external) DSP Bypass.
List Price: $3495.00 list