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Thread: Measuring the frequency response of tape playback electronics

  1. #1
    [Industry Expert] Senior Member Fred Thal's Avatar
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    Measuring the frequency response of tape playback electronics

    For an end user of a tape repro electronics to do this, we'll assume the use of a reproducer alignment tape, a so-called calibration tape.

    Yet a limitation with the popular cal tapes is the too sparse distribution of frequencies.

    So, if you were a qualified designer of tape electronics (or someone seriously wanting to investigate the performance of any tape electronics) you wouldn't accept only 13 discrete spot frequencies to examine the response because you wouldn't get an accurate picture. You'd insist on about ten times as many! (We're talking one-twelfth octave resolution.)

    Is anyone thinking: Wouldn't this measurement take all day to accomplish?

    No, it would take under two minutes.

    Actually, under 25 seconds for a 20kHz to 20Hz, 112-step sequenced test signal, using this 35-year-old hardware, with its specified cal tapes (from MRL):

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    Well, pardon the big marketing sign. I didn't want to edit the image. The (quickly obtained) resulting plot on the ST 1510A is saved and examined.

    Or, printed and shipped with the product as its proof of performance.

    Which of the newer tape electronics manufacturers are doing this?

    (The respected older ones did.)
    Last edited by Fred Thal; 01-01-2018 at 05:02 PM. Reason: correction: under 25 seconds
    Adolph Friederich (Fred) Thal
    Technical Director and Founder, Audio Transfer Laboratory
    Managing Director, ATAE ataudioeng.com

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    VIP/Donor [VIP/Donor] microstrip's Avatar
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    Quote Originally Posted by Fred Thal View Post
    (...) Which of the newer tape electronics manufacturers are doing this?

    (The respected older ones did.)
    They could easily do it if they wanted - any inexpensive modern soundcard based audio spectrometer can record and analyze such signal.

    The real advantage of the 1510A is that for an experienced user it can be faster and more efficient - just one box, optimized for these particular tasks. But currently inexpensive virtual instruments can be very powerful.

    BTW, audiophiles are usually only concerned with playback of pre-recorded tapes.
    DCS Vivaldi 2.0 stack, Apogee Duetta Signature while waiting for the XLF successor, Forsell Air Force One, ARC Phono 3, Lamm ML1.2 Ref, Lamm L2ref, TA OPUS MM2 IC's and sp, TA XL digital, TA XL gen V power cables, CenterStage footers and Nordost Qkore8's!

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    [Industry Expert] Senior Member Fred Thal's Avatar
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    Quote Originally Posted by microstrip View Post
    They could easily do it if they wanted -
    The real audio people here already know that when plugging in something new (like a tape stage) and everything immediately sounds very different, the first thing to check are the level and response matching between the two units being compared. Only if you do this first, can you then make meaningful evaluations about sound quality differences.

    This is easy to do with tape, fortunately!

    That's what this thread was going to be about, but no one cares?

    The first Studer A820s that I saw modified for switch-controlled selective use of internal or outboard audio electronics, were owned by one of the Big Three, here in the States. This was 25 years ago. The mod was actually competently engineered and executed, done by people who fully understood what they were doing. I took a lot of notes.
    Adolph Friederich (Fred) Thal
    Technical Director and Founder, Audio Transfer Laboratory
    Managing Director, ATAE ataudioeng.com

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    Addicted to Best! christensenleif@msn.com's Avatar
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    I care and would like to hear the rest.....
    best
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    Fred,

    If I want to do this properly, what else do I need apart from the ST1510A plus suitable MRL tape? It seems quite hard to find a ST1510A in the UK or Europe. Is there another machine I could use instead?

    Thanks

    Charlie
    R2R: Studer A820 1/2 inch 2 track; Otari MTR-12 1/4 inch 2 track; Sony APR 5003; Sony APR 5002; Studer A807/II. Vinyl: Platine Verdier Allaerts MC1B/Schroeder Model 2 Decca C4E/Hadcock 228 TRON Seven Reference phono. Other analogue source: Nakamichi Dragon with ANT4066 mods. Amplification: TRON Meteor preamp TRON Voyager 20B SET power. Speakers: Avantgarde Duo. Digital: does not compute

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    [Industry Expert] Senior Member Fred Thal's Avatar
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    Quote Originally Posted by topoxforddoc View Post
    Fred,

    If I want to do this properly, what else do I need apart from the ST1510A plus suitable MRL tape? It seems quite hard to find a ST1510A in the UK or Europe. Is there another machine I could use instead?

    Thanks

    Charlie
    Hi Charlie and Leif,

    You definitely do not need to go try to find an old ST 1510A.

    microstrip (sorry, do not know his or her real name) who posted to this thread had it exactly right.

    If you don't mind an excursion into the digital domain, the instrumentation available today for audio signal analysis is amazing in its accuracy, its versatility and its low cost. Bottom line is for audio testing DSP is your friend!

    The truth is, I only keep the old 1510As on line here for the sheer fun of it. (It's an early Zilog microprocessor based instrument!)

    On the Audio Science Review forum today, Amir is beginning to investigate how to properly measure tape playback electronics using MRL cal tapes. Rather than try to duplicate the postings from that forum here, I suggest you plan to read the goings on over there.

    Unfortunately, it's in a thread called Phono Pre-amp: What are we testing for?

    I think I'll suggest a new thread title there.
    Adolph Friederich (Fred) Thal
    Technical Director and Founder, Audio Transfer Laboratory
    Managing Director, ATAE ataudioeng.com

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    VIP/Donor [VIP/Donor] microstrip's Avatar
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    Quote Originally Posted by topoxforddoc View Post
    Fred,

    If I want to do this properly, what else do I need apart from the ST1510A plus suitable MRL tape? It seems quite hard to find a ST1510A in the UK or Europe. Is there another machine I could use instead?

    Thanks

    Charlie
    Even if you manage to get these old measuring machines, it is very hard to keep them working properly and calibrated. If you are an occasional user I would suggest an USB good quality ADC/DAC (yes, I know it is an heresy to use such words in a tape thread ) - even some of the inexpensive are accurate to .1 dB and some software with recording and processing capabilities. I like SpectraPlus, but I have seen people using several others.
    DCS Vivaldi 2.0 stack, Apogee Duetta Signature while waiting for the XLF successor, Forsell Air Force One, ARC Phono 3, Lamm ML1.2 Ref, Lamm L2ref, TA OPUS MM2 IC's and sp, TA XL digital, TA XL gen V power cables, CenterStage footers and Nordost Qkore8's!

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    I have a Focusrite Scarlett 2i2 usb audio interface, a Mac and Audacity. Is this what I have to do?

    1) Plug the outputs from the R2R into the XLR inputs on the audio interface
    2) Launch audacity from the interface on my Mac
    3) Play a test tape, whilst recording on audacity
    4) Then review this on audacity with the analyse - plot spectrum

    Thanks

    Charlie
    R2R: Studer A820 1/2 inch 2 track; Otari MTR-12 1/4 inch 2 track; Sony APR 5003; Sony APR 5002; Studer A807/II. Vinyl: Platine Verdier Allaerts MC1B/Schroeder Model 2 Decca C4E/Hadcock 228 TRON Seven Reference phono. Other analogue source: Nakamichi Dragon with ANT4066 mods. Amplification: TRON Meteor preamp TRON Voyager 20B SET power. Speakers: Avantgarde Duo. Digital: does not compute

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    Hi Fred,

    Have i got this correct?

    Thanks

    Charlie
    R2R: Studer A820 1/2 inch 2 track; Otari MTR-12 1/4 inch 2 track; Sony APR 5003; Sony APR 5002; Studer A807/II. Vinyl: Platine Verdier Allaerts MC1B/Schroeder Model 2 Decca C4E/Hadcock 228 TRON Seven Reference phono. Other analogue source: Nakamichi Dragon with ANT4066 mods. Amplification: TRON Meteor preamp TRON Voyager 20B SET power. Speakers: Avantgarde Duo. Digital: does not compute

  10. #10
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    What you need to do depends on which MRL tape you have. You also need to tell which deck this is for and the speed/EQ you will be adjusting for.

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