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Thread: Early analogue recordings & an evaluation of analogue technology ...

  1. #41
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    Default

    Quote Originally Posted by A.S. View Post
    I'm a bit surprised your golden-olden ears didn't detect this - the burbling in the lineup tone gave the game away...
    I've listened to quite enough line up tone, thanks - I whizz through it these days

    Actually, the LF burbling was more obvious on the decay at the very end of the off-tape clip, now that I've actually listened to it all the way through (too impatient, that's my trouble).

    If that really is the off-tape response of the Revox, very impressed. Also with the fact that you have a still viable supply of Type 200 - exactly which version? The best one was probably Agfa PEM something-or-other and there was also Zonal - rather more variable in sensitivity.

  2. #42
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    Default Type 200 lives - or exists anyway - at Harbeth

    Quote Originally Posted by Pluto View Post
    ...If that really is the off-tape response of the Revox, very impressed. Also with the fact that you have a still viable supply of Type 200 - exactly which version? The best one was probably Agfa PEM something-or-other and there was also Zonal - rather more variable in sensitivity.
    Surely you don't want me to turn the video onto the switch and watch the input/off tape action do you!

    Plenty of *brand spanking new* Type 200 here on 5" and 10" reels. You're alluding to BASF SM468 and Zonal 675. The sensitivity of the Zonal is slightly lower.
    Alan A. Shaw
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    Harbeth Audio UK

  3. #43
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    Default Revox mods

    Quote Originally Posted by A.S. View Post
    Surely you don't want me to turn the video onto the switch and watch the input/off tape action do you?
    No - I trust you - but I would be interested in seeing the HFN article. What was the essence of the modification to get it that flat?

    The remarkable thing about the tape is not that you have it, but that it remains usable without shedding the oxide.

  4. #44
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    Default Modifications to the Revox B77 to make flat replay

    Quote Originally Posted by Pluto View Post
    ...but I would be interested in seeing the HFN article. What was the essence of the modification to get it that flat?
    As I recall, I considered modifying both the record EQ and the replay EQ. The normal attack on designing tape recorder electronics is to standardise the replay EQ so that a known calibration tape will replay with the correct frequency response regardless of the machine it is replayed on and to adjust the record EQ by whatever means and manner is expedient to make a tape recorded on that machine (after aligning the replay performance) replay as flat.

    In the case of the Revox, in comparison with the much more adjustable Studers, there are no user adjustments (if I recall) for record or replay EQ. So I modelled in software and then reworked the record electronics to increase the drive to the head at audio HF a little, so that the record/replay result was flat.

    This B77 was made with NAB standard electronics (and still has) but the CCIR/IEC standard is used in the BBC and on my Studers. My AEG Telefunken M21 is programmable for either across a wide range of speeds up to and including 30 ips.: very sophisticated design.

    The M21 weighs 45kg despite its compact size and it just wasn't possible to bring it into my den. Literature attached. Mine is like the reverse-head unit shown on the cover: that means the magnetic oxide side of the tape must be outwards, not inwards. I believe this is popular in Europe.

    >
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    Alan A. Shaw
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    Harbeth Audio UK

  5. #45
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    Default Dolby noise reduction

    Yes, having recorded 400 Hz Dolby tones, the burbling was a dead give away. Speaking of Dolby wasn't the use of the professional "A" and consumer "B&C" quite common in the later days to improve the signal to noise ratios?

  6. #46
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    Default Convert a digital recording to analogue ....

    So, if we take a recording that was originally created in a digital format and then for marketing purposes released in vinyl format, what would the comparison look like? Dianna Krall -Live in Paris, Dire Straits - Brothers on Arms...

    Cheers

    George

    {Moderators comment: Unmistakeable fact that the lower resolution potential of analogue (because of hiss masking microtones) means that information will inevitably be erased. It would be like painting a picture from an existing high-res photo. Makes no sense at all except on an emotional level.}

  7. #47
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    Default Dolby noise reduction made multitrack audio possible.

    Quote Originally Posted by Don Leman View Post
    Speaking of Dolby wasn't the use of the professional "A" and consumer "B&C" quite common in the later days to improve the signal to noise ratios?
    In exactly what context?

    Professionally, it was Dolby A that made the widespread use of 16++ tracks possible at all - without it (or a similar system) it is likely that multi-track technology and technique would not have developed as it did. Given the inherently poor noise performance of analogue tape (which could be improved a little by increasing the tape speed, a process analogous to noise shaping in the digital domain), you couldn't really mix that many tracks at unity gain before the noise build up started becoming intrusive. Dolby A offered 10-15dB of improvement and became available, ISTR, in the middle sixties. The earliest units were 4 or 5U high for two channels, so a 16 track installation was extremely expensive and occupied an entire bay.

    Dolby B was the somewhat simpler implementation that rapidly found favour with users of domestic cassette equipment. One particular issue never really cracked was the need for the threshold of Dolby operation to be at a fixed level of modulation on the tape to ensure broad compatibility between tapes of differing sensitivity. While most of the better cassette machines included the necessary tone generator and adjustments, getting consumers to perform a routine "line up" didn't really work.

    A late model Revox A77 included a Dolby B option - I don't recall if the B77 ever offered this - but I don't think it sold that well although the achievable results could be spectacularly good for that time. One big difficulty, alluded to in Alan's earlier demonstration, was that lowering the noise floor (and Dolby B only affected relatively high frequency hiss, whereas Dolby A benefited the entire audible spectrum) ensured that the other weaknesses of analogue recording merely became more apparent.

    There is a very good article on Wikipedia that covers the gamut of Dolby's analogue NR schemes. As happens so often with technology, the really good systems (SR for pro., S for domestic) came along too late for widespread adoption. By then, the march toward the digital world was unstoppable.

  8. #48
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    Default Write-up on the B77 from HiFi News ....

    I found my original HiFi News article from Feb. 1997 describing the very Revox B77 that I've been using in the video talk-throughs in this thread nearly fifteen years later.

    Article attached.
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    Alan A. Shaw
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    Harbeth Audio UK

  9. #49
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    Default Adding noise to a digital recording to give it the 'analogue sound'?

    Quote Originally Posted by Macjager View Post
    So, if we take a recording that was originally created in a digital format and then for marketing purposes released in vinyl format, what would the comparison look like? Dianna Krall -Live in Paris, Dire Straits - Brothers on Arms...

    Cheers

    George

    {Moderators comment: Unmistakeable fact that the lower resolution potential of analogue (because of hiss masking microtones) means that information will inevitably be erased. It would be like painting a picture from an existing high-res photo. Makes no sense at all except on an emotional level.}
    Now, based on earlier comments by Alan, would the recording company actually add noise to the digitally mastered and digitally released recording, intentionally masking the full range of digital information, in order to make it sound more analogue...thus the vinyl and the digital release will sound (almost) the same...nefarious aren't they...

  10. #50
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    Default In appreciation of your posts..

    Alan,

    Your posts were one of the main reasons, I was convinced to invest in Harbeths. All I had to go on otherwise was a distant memory of having heard Harbeths about 5 years ago for a few minutes when a customer was taking delivery from your dealer in Singapore. There were no dealers in India till recently.

    So not only do you have an appreciative audience for your posts, I think it is excellent marketing (and certainly different from the variety to referred to in this thread earlier!). They are a very viable ambassador for Harbeth, especially in places where access to a dealer/ distributor is limited.

    Apart from that, thank you for the learning you are imparting here. As has been mentioned by others earlier, it is really appreciated.

  11. #51
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    Default Dolby and noise

    Quote Originally Posted by Pluto View Post
    In exactly what context?
    I guess the context would be the response of the recording industry in recognizing the limitations of analog recording. I expect the samples Alan provided would have been not quite as easy to identify if Dolby noise reduction was used for the analog sample.

  12. #52
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    Default Noise reduction systems

    Quote Originally Posted by Don Leman View Post
    I guess the context would be the response of the recording industry in recognizing the limitations of analog recording. I expect the samples Alan provided would have been not quite as easy to identify if Dolby noise reduction was used for the analog sample.
    I don't fully agree. I have several Dolby A encode/decode units and also Dolby SR modules, which as you may have read in Pluto's post, represented the last word in noise reduction - at very considerable expense. I was going to comment on my experiences with them later.

    In essence, what the Dolby A/SR system does is that it tries to work around the rather annoying hiss limitations of analogue tape. The genius of Ray Dolby's noise reduction system is that it is based on a proven understanding of how the human ear works, and particularly, how it can be fooled. It cannot improve upon the analogue (medium) tape - that's fixed with all it's problems - so all it can do is fiddle around the edge of the problem 'bending' the analogue limitations until they are less obvious. But boy, are they still there.

    Undoubtedly, the application of Dolby noise reduction - as we all know from the Dolby B system with audio cassettes - really does clobber hiss. It does that without (too much) effecting tonality by a complimentary encode/decode process that (in theory) can adapt to the wider range of replay levels as you would find in consumer cassette decks playing audio cassettes that have no calibration line-up tones recorded onto them. The total absence of a known reference magnetic level means at the consumer's end means that the Dolby system is unlikely to be working optimally, but switching it in/out clearly proves that it does work. So how?

    Basically, the system is intelligent in that it senses instant by instant how loud the signal is in a number of well defined audio bands. Then it boosts or cuts the level according to a defined method. For example, at the encode stage, if there is moderate energy in the midrange it would boost the signal in that band and then during replay would apply the exact same level reduction. As the gain is reduced on replay so the hiss level would, to the listener, diminish as well simply because there was less output in that band. No magic there. But, I had hoped to show in my examples that hiss is just one issue. The encode/decode process cannot remove much hiss - certainly not where there is already a strong signal and little boost dare be applied during encode) - and even so, it does nothing for sonic resolution. As I showed with the digital noise floor at perhaps -100dB and the analogue hiss at perhaps -50dB, the bottom 50dB (or let's say more generously, allowing 10dB of hiss reduction) 40dB of the audio signal is simple obliterated by the hiss even with a Dolby NR system. But recording the tape louder in certain bands significantly increases distortion, and that means harmonics not present in the original audio now appear off-tape (quite alarmingly level dependent) and signal compression now becomes an issue. So, as with all audio issues, the major irritant is solved, but numerous additional issues now rear their ugly heads.

    I found the professional Dolby SR system to be really rather interesting. When carefully aligned for exact mirror encode/decode on my Studer 807 (an afternoon's work) there is an eerie silence decode-replaying an analogue tape. It really is, as the sales brochure said, as quiet as digital. But listen more closely and what you notice is that there just isn't any fine detail. That's perfectly OK for pop recording, but for classical, it just doesn't sound as we expect. But it certainly is an analogue marvel.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  13. #53
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    Default How do MP3-like systems compare with analogue?

    Over the past few days in spare moments, I've been examining how MP3 type data reduction systems behave when presented with pure tones. I've been curious about how they have used the underlying reality of noise-masking* to throw-away signal information that would be inaudible, buried under the background hiss as is the case with normal analogue media. What about mini disk's ATRAC system?

    Perhaps I'll make another video talk to show what I've found? Probably best to start another thread.

    *Noise masking means that quieter sounds are completely hidden and undetectable to the human ear by the presence of other (louder) sounds. No signal information can be heard once it is at or below the background noise-floor of an audio reproduction system, so it is a pointless exercise to provide a dynamic range significantly greater than the reality of the signal-to-noise range of the media being replayed.
    Alan A. Shaw
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    Harbeth Audio UK

  14. #54
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    Default The genius of Dolby

    Quote Originally Posted by A.S. View Post
    The genius of Ray Dolby's noise reduction system is that it is based on a proven understanding of how the human ear works, and particularly, how it can be fooled
    Another, possibly more important, demonstration of Dolby's intellect is given by the fact that, unlike a great many of the "competing" NR systems that became available around that time (DBX, Burwen & one or two others), Dolby only sought quite a modest 10 - 15dB improvement.

    The others offered a rather greater paper NR figure yet were not commercially successful (largely on account of their inability to operate transparently).

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    Default So inexpensive, not worth cheating

    Quote Originally Posted by Pluto View Post
    Another, possibly more important, demonstration of Dolby's intellect is given by the fact that, unlike a great many of the "competing" NR systems ...
    And another, perhaps even more astute decision was to offer a licence (per decoder IC built into a Dolby B/C/S deck) of just one or two cents which was collected from the IC manufacturer and could be audited.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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