What is PRaT?

September 18, 2021
 by Paul McGowan

19 comments on “What is PRaT?”

  1. PRaT and resolution of finest details are my primary criteria for a good stereo systems. However I still struggle getting an explanation why some vinyl records give me a huge degree of PRaT while the digitized recording released from the same record label renders no PRaT at all. Either the analog reproduction path adds PRaT or there is something fundamentally wrong with the digitization or the DAC process. I guess the latter is the case and Paul McGowan or Ted Smith should be able – being renowned pioneers in digital audio – to give a logical explanation. I hope the coming top tier DAC designed by Ted Smith will be a real PRaT machine! By the way: I got always more PRaT from my first turntable (Revox B790) than from several LINN LP12s – the owners then always argued that an LP12 needed most careful set-up and daily fine-tuning being most sensible concerning room temperature.

    1. Thanks, Paul. Yes, PRaT is an interesting indicator of something we’ve not yet put our fingers on. What we know is it is held back if there’s harshness or irritations in the music and we know it is not enhanced when things in the reproduction are amiss. What we don’t know is how to amplify or ensure it.

      1. I am pretty sure that having now on board Gus Skinnas and the team of Octave Records and the IRSV-Killer you have established the best preconditions to find the solution!

    2. The Revox was my first serious turntable supplied with an Ortofon VMS20 cartridge after the Pioneer PL12D. Unsurpassed in my opinion for ease of use.
      Now I am on a Project RPM 5 Carbon retrieving much more detail, but still fond memories of the Revox!

      1. I upgraded my Revox TT with a Shure V15 IV cartridge – the integrated damping element seemed to be mandatory for the short tonearm when tracking non-flat vinyls – and a remote control for lifting and shifting the tonearm. And of course I replaced the original tonearm-cable which then was directly connected to the phono preamp without any interruption. 🙂

  2. It would be interesting to know which technical aspects of audio products are responsible for the audible phenomenon referred to as PRaT. It’s certainly nothing to do with clock stability or jitter.

    1. Pace and Timing are somehow related with transients the most dominant character in music especially for percussions and plucked instruments. Could it be that “digital” effects as pre-ringing known from digital reconstruction filters render a completely unnatural timbre?

      1. Good afternoon paulsquirrel!
        To answer the first question you asked.
        The real truth is, sense 1953, record companies here in the US, used a scheme called RIAA equalization.
        That’s been the narm sinse then.
        Digital recordings of any kind, doesn’t use RIAA equalization.
        I guess that’s why you don’t hear it in digital recordings.

        1. According to Michael Fremer the sound quality of a vinyl record isn’t much degraded when he makes digital copies for his demonstrations. I have made similar experiences. Thus I made several proposals for an answer: either the analog mastering process is totally different including the RIAA EQ. Or there are basic differences between digital and anlog recordings.Or the analog reading of the grooves add specific distortions we like. Who knows? But I am sure, Paul and his team know the answer – at least when Gus Skinnas has revealed his tricks for mixing and mastering! 🙂

        2. RIAA equalization is an example of pre-emphasis in the recording chain and de-emphasis in the playback chain. Use of pre-emphasis goes back to the 1920s. In the early days there were many different schemes, and some phono amplifier provide selectable de-emphasis for each of the major record companies. As John reminds us, the equalization schemes became more or less standardized in the 1950’s, and we tend to use “RIAA” to refer to the winner in that particular standards war.

          In a properly designed implementation, the combination of the pre-emphasis and the de-emphasis provides a flat end-to-end response.

            1. Hi John. The velocity of the disc cutter is proportional to the voltage applied. The displacement of the cutter is proportional to the voltage applied and inversely proportional to the frequency of the signal. Without the pre-emphasis, the grooves in the disc would be impossibly wide at low frequencies, and so tiny at high frequencies that the signal would be completely lost in the noise. The input to the cutter is therefore filtered with an inverse-RIAA curve which cuts the bass and boosts the treble.

              The pick-up cartridge is also a constant velocity device. The RIAA equalization in the phono pre-amp is the exact complement of the pre-emphasis applied at the input to the disc cutter.

              Of course, this approach is vulnerable to rumble in the turntable, because low frequencies are heavily amplified on replay.

  3. I’m not a big fan of made up terms like PRAT. But my most important audio qualities are clean transients, fast starts and especially clean decay, and dynamic linearity, lack of compression for all level changes from small to huge. Interestingly these are the factors maintained outside a room where music is coming from whether it’s recorded OR live. It’s not frequency response.

  4. Several responses here propose super-fast attack being of the essence.

    We do know that it is a major influence on our perception of timbre

    So what if a good moving coil cartridge is ‘quicker’ than 16/44.1 digital? Well Reference Record ‘Prof’ Johnson measured the rise time of a MC and was surprised at how fast it was.
    He was also involved with some Spectral pre-amplifiers whose claim to fame is megahertz bandwidth along with 1200 Volts/ microsecond !!!

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