Linn Products is a very famous UK high fidelity equipment firm. It really came to prominence in the 1970s in making the argument that the turntable had been overlooked as a critical component in the playback chain. It’s contribution at the time was the highly regarded Linn Sondek LP12 turntable. Linn products typically manage to include a ‘k’ in their names.
Nowadays Linn has quite a line-up of digital products in addition to its analogue ones, but back in the day its founder Ivor Tiefenbrun was a prominent exponent of the supposed deficiencies of digital audio.
On a visit to Canada in 1984 his claims were put to the test, via double blind listening tests, as reported by the Boston Audio Society.
In each case his assertions as to being able to hear particular phenomena proved unfounded. Of particular interest: they did an ABX test using LPs on a Linn/Naim/Linn system, comparing straight-through with an ADC/DAC inserted into the signal path. No positive results for that either. The ADC/DAC was as basic as you could get: a Sony PCM-F1 VCR-based recorder. By ‘basic’, I am comparing with today’s standards. Back then it was so cool to have a relatively inexpensive, relatively portable way of recording real, actual digital content.
But basic it was: 44.1kHz sampling and (according to the linked article, although I hadn’t realised this) only 14 bits of resolution.
Here was the first test:
The gains of the “A” and “B” paths were matched in both left and right channels to within 0.05 dB at 1 kHz using the PCM-F1’s gain controls. This was done by measuring across the amplifier output terminals. The match was then confirmed to be within ± 0.25 dB across the whole audio band. The PCM-F1’s “peak hold” feature was used to keep a record of the peak signal levels passing through it during the test, especially in view of the relatively high sensitivity of the Naim power amplifier (<1 Vrms at clipping) and the relatively low listening levels chosen by the participants. More about this shortly. After an acclimatization period, a set of 10 trials was conducted in an unhurried fashion before breaking for lunch, after which a further set of 10 trials was conducted. Tiefenbrun's score for the series was 11 correct decisions out of 20, a result which shows no statistically significant ability to discriminate between "A" and "B" any more accurately than would be expected on the basis of random guessing. At this point I thought that I could reliably distinguish between the "A" and "B" paths on the basis of the slight noise level increase which occurred when the PCM-F1 was inserted into the chain, and which was marginally audible due to the high gain of the Naim MAP 250 power amplifier combined with the low peak signal levels through the F1, which the peak-hold meters showed to have risen no higher than -20 dB. (0 dB is the digital clip point, and these peak levels were somewhat unfair to the digital processor since 20 dB of its signal-to-noise ratio was being thrown away.) [In other words, for this segment of the test the F1 was in effect a 13-bit processor. - Ed.]
Actually, ‘Ed.’ is being a little kind. If you’re running a digital capture system with 20dB of headroom, then your new effective ‘Full Scale’ is some 3.32 bits below the theoretical FS. So the ADC/DAC cycle was running at 12.68 bits.
BUT, if the link above is correct (and Wikipedia seems to confirm it), and the PCM-F1 used 14 bits, then the system was effectively 10.68 bits. That would give it a noise floor of around -64dBFS, which the author of the article could hear, but would not be obvious when playing an LP, since the noise floor of LP’s is typically higher.
Do read the whole article because they continue the test with very interesting results.
Note: this test does not prove that digital conversion is inaudible. But should be easy enough to prove the deficiencies of digital audio — if there are any — with a suitable double blind test, and the lack of tests with clear positive results is suggestive.