Triple Bypass Part-3

The rest of the measurements, some conclusions, and a few somewhat relevant pontifications

Along the left side are the remaining 9 image captures of the Voxengo SPAN tool showing the signal-present gain and harmonic behavior of the three devices we're testing. 

 

Having shown three ways the X32 preamps can be bypassed (hence the name of this article series) the lessons that can be learned from this exercise cover quite a lot of ground.  Of foremost interest to those who want to bypass the X32 preamps, the graphs show that using the digital trim TRS inputs is actually a poorer decision than using the XLR/preamp inputs.  The Behringer X32 preamps have noise floor that in all practical ways is as quiet as other good preamps and the TRS inputs are noisier by enough to make the XLR input the preferred choice.

Another lesson is that the Midas preamps are different from the Behringer ones in the presence of a signal. Note that the peak 3rd harmonic of the Midas preamp when driven with a -6dBFS signal, is fully as small as the 3rd harmonic of an X32 preamp transferring a -18dBFS signal.  It shows the Midas to be significantly cleaner when passing signals.  That difference in cleanliness is very likely why the Audient and Midas (whose measurements are more similar than not) have the loyalty that they’ve earned.  It’s much harder to see the difference when these products are providing gain, but our ears are able to discern a quality difference enough to pay for it. 

This brings us near the philosophical considerations of diminishing returns, good-for-the-money, and other value judgements that transcend what we can see on an oscilloscope.  Being dismissive of the solid capability of the X32 preamps requires that the importance of this reliable data be ignored, so the sins of the old Behringer product line can remain unforgiven.  There is unfortunately, a large population within the audio market that staunchly retain this implacable stance.

Once a brand has been cheapened (e.g. Lincoln, Cadillac) the uphill climb back to customer trust and respect takes quite a long time.  Once a brand has been associated with low cost (e.g. Volkswagen, Kia, Hyundai), the climb upmarket (Phaeton, K900, Equus, respectively) is a ladder with greased rungs, and not many make it.  These marketing and human behavior lessons from the auto industry have applicability to the behavior of the audio industry, both in the consumer and professional arena.

 

--- Warning, Pontifications in Paragraphs Below --- 

The music industry got along just fine with captivating recordings of pianos and brass bands without imploding from the stability‑challenged tape transports of the time. To make the point, any company that introduced a new audio interface today with the specifications of the mighty and well-regarded ($60,000 in the 1980’s) Studer A827 would have to turn up their Apple earbuds to drown out the shocked laughter.

This beautiful machine (I want one, by the way) draws up to 1100-watts, has around 1-percent (3rd harmonic, ‑40dB) distortion at each of its 3 speeds, and tops out with a best‑case 74dB signal‑to‑noise ratio (about 13 bits) at 30-inches per second. Frequency response between 50Hz and 20 kHz is plus/minus 1dB or 2dB depending on tape speed, getting down flatter to 30Hz if you run at 15 or 7.5 inches per second.  Also keep in mind that all the music rode in upon the tape bias frequency of 153.6kHz; an often ignored part of the arm-waving from people who want to argue that the signals captured on the tape were in some way more purely managed than today's musical delicacies suffering the brutality of digital sampling.

As for speed stability, the tape machine's wow and flutter specification of 0.03-percent has a fairly complex relationship to the equivalent problems of clock stability and jitter in the digital world.  Suffice it to say that a pair of mechanical rotors cannot be as stable as a tuned crystal circuit. I'll save that discussion for another day.

Why do I still want one?  Because I've learned that a little distortion of the right kind in the right amounts is actually quite wonderful (euphonic) stuff.  By analogy, consider the market for water. Spring waters and mineral waters contain trace amounts of sodium, calcium and magnesium, which contribute to their refreshment, while distilled water in its purity can actually be a bit off‑putting. 

Classical music was a strong market for the newfangled CD with its lower noise floor, so moving away from tape was a good tradeoff, and we saw a strong first-mover response within that market segment.   Rock and jazz benefited much more from the ‘head bump’ bass enhancement, complex compression, and 3rd harmonic flavorings provided by tape, so the critical listeners’ market wasn't quite as enthused about moving away from the embrace of tape to the cold world of digitally captured music.  How’s that for summarizing three decades of technological development and market transformation in two sentences?  I want it all!  I want the convenience of digital recording, and the sweetness of tape, without the hiss.  Right now, I routinely use up to four different tape emulator products in my mixes; many times with a couple cascaded one through another because no single product gives me the exact character that I want.

Sorry about the lack of balloons and ice cream.  My SCIMITAR (Superscalar Converter of Insentient Material for Immediate Transport and Reassembly) isn’t working (yet).  There is, however, an article series in the works that attempts to use the water analogy above in a unique way.  I hope to develop a convenient data collection method that allows me to scale the 2nd, 3rd and 4th harmonics through an RGB color generator, so I can consistently display the actual 'color' of a preamp.  Essentially, I'm attempting to work out a computer-based synesthesia tool for preamps.  It'll be fun for sure!  Now what would be a cool acronym? Hmmmm...

Thanks for your attention,

- Ted Gary of TedLand

April 26, 2017

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