Exploring the limits of sound quality hidden in analog master tapes requires playing the tapes back on a system that is adding almost no distortion.
Amplitude versus time, the introductory science of analog audio tape playback
There are two predominate common distortions introduced in the playback of analog audio tapes.
The first is time base corruption (also called wow and flutter and pitch change). This is observed as unwanted frequency modulation and frequency shift.
The second is frequency response error, observed as a non-linearity of magnitude plotted across the frequency spectrum.
Both of these distortion types are easily measured with instrumentation.
Both are readily detectable by trained critical listeners.
Minimizing the playback distortions
Reducing the time base corruption introduced in playback is accomplished by improving the quality of the tape transport mechanism. This turns out to be costly, but improvements made here also lead to improvements in signal amplitude stability. For example, scrape flutter doesn't only contribute unwanted frequency modulation, it also introduces unwanted amplitude modulation.
Modern FFT spectral analysis for quantifying the time base accuracy of analog audio tape transports (suggested by D. Manquen) uses a 12.5 kHz carrier signal that is four times higher in frequency than the wow and flutter measurement standards historically employed. This broadens the measured bandwidth to reveal scrape flutter, once erroneously believed inconsequential to the perceived sound quality of recorded music.
A reference-quality tape transport mechanism
It's been known for fifty years that a tape transport that introduces the lowest time base corruption requires a servoed constant-tension, servoed capstan, precision guidance design fitted with a precision headblock using no forced guidance. Yet because of the prohibitively high cost of manufacture, less than one-half of one percent of all professional audio tape machines ever made were of such design.
Reference-quality playback electronics
Once a reference-quality transport is available, correcting frequency response errors becomes possible. With the transport contributing near-perfect (not forced) tape guidance with low scrape flutter generation and high dynamic azimuth stability, optimal playback quality can be realized with low-noise, low-distortion playback electronics that accurately follow the industry’s established equalization curves.
Meet the reproducer
The machine we're describing is not a recorder. It's optimized for highest-quality playback and it’s known as a reproducer. A professional quality reproducer must also offer accurately adjustable tape tensions and capstan speed trim.
One could attempt to build new, state-of-the-art reproducers from scratch, but the cost of small-scale manufacturing of the precision mechanical components could be prohibitive. So it's more practical to modify and re-manufacture the very best tape transports from the past.
A survey of the best-in-breed analog audio recording instruments incorporating the necessary design features will quickly illuminate the famed A80 and A820 transports from Studer in Switzerland. Hence our exacting re-manufacturing program based exclusively on these two legendary models.
We're finished only when the new transport has time-base accuracy exceeding the original Studer specification by almost an order of magnitude.
We manufacture audio tape playback systems as described here. Pricing starts at $95,000. We began this work in 1987, making this our thirty-second year.
Please get in touch to learn more about our state-of-the-art analog audio tape product offerings.
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