[sdiy] "Digital vs analog waveforms" [was: Ways for innovation]

Simon Brouwer simon.o at brousant.nl
Fri Jan 29 09:31:29 CET 2016 

Hi Chris,
 
Thanks for pointing that out.
 
It is true that AC bias had been invented earlier, but Weber surely did not know
about it, and my point is that this is a really nice example of serendipity.
 
This stroke of luck was only part of the story though, Weber was also a very
capable engineer who took a leading role in developing his discovery into
practical application.
 
Best regards
Simon
 

> Op 29 januari 2016 om 2:26 schreef Chris Juried <cjuried at yahoo.com>:
> 
>  Hi Simon,
>   
>  That is a common misconception. AC bias was originally discovered in 1921 by
> US Navy engineers Carlson and Carpenter. But they were “before their time”,
> and ac bias was forgotten for almost 20 years. Then around 1938...1941, ac
> bias was independently rediscovered and reported by Japanese engineers Nagai,
> Sasaki, and Endo in 1938; German engineers Braunmuhl and Weber in 1941; and
> American engineer Camras in 1941.
>   
>   
>  Sincerely,   
>    
>  Chris Juried  
>  Audio Engineering Society (AES) Member 
>  InfoComm-Recognized AV Technologist
>  http://www.JuriedEngineering.com http://www.juriedengineering.com/  (Juried
> Engineering, LLC.)
>  http://www.TubeEquipment.com http://www.tubeequipment.com/ (Tube Equipment
> Corporation)
>  http://www.HistoryOfRecording.com http://www.historyofrecording.com/ (History
> of Recording)
> 
> 
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> 
> 
> 
>  ---------------------------------------------
>  From: Simon Brouwer <simon.o at brousant.nl>
>  To: synth-diy List <synth-diy at dropmix.xs4all.nl>
>  Sent: Thursday, January 28, 2016 3:34 PM
>  Subject: Re: [sdiy] "Digital vs analog waveforms" [was: Ways for innovation]
> 
>  Hi Sarah,
>   
>  That is a nice insight, I had never thought of AC bias working that way.
>   
>  I like the story of how German radio engineer Walter Weber, who worked with
> early AEG tape recorders in 1940, discovered AC bias. At that time, wire and
> tape recorders had appalling reproduction performance, but all of a sudden his
> recordings became of amazingly good quality. It turned out this was actually
> caused by a defective amplifier circuit which broke into strong HF
> oscillation.
>   
>  Best regards
>  Simon
> 
>  > Op 28 januari 2016 om 16:38 schreef Sarah Thompson <plodger at gmail.com>:
>  >
>  >
>  > It seems to me that nobody ever really acknowledges that analog tape
>  > actually also samples the recorded signal in time, though doesn't quantize
>  > in level. The bias signal, usually a sine wave at 50 - 100KHz or so, is
>  > added to preemphasized version of the audio as it is fed to the record
>  > head. This overcomes the large amount of hysteresis in the magnetic
>  > materials in the tape by rapidly flipping between linear(ish) regions. This
>  > overcomes the coercivity of the iron oxide, but has the side effect that
>  > the audio is only really recorded during the peaks of the bias signal.
>  > Though not identical to digital sampling, this does still cause very
>  > similar aliasing issues, so the signal path still needs antialiasing
>  > filters, even though they are typically not thought of as such.
>  >
>  > This is also why higher bias frequencies often sound better, though were
>  > harder to achieve due to the relatively high voltages needed.
>  >
>  > Sarah
>  >
>  > Sent from my iPad
>  >
>  > > On Jan 27, 2016, at 6:16 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
>  > >
>  > > I expect he's just saying that he likes a nice clean 16-bit/44.1KHz CD
>  > > over a noisy old cassette tape. Hard not to agree, really. Especially
>  > > once the tape's been in the back of a cupboard unloved for a few years
>  > > and has print-through to boot. That's "degradation of stated media", I
>  > > suppose.
>  > >
>  > > Still, even offered a brand new consumer cassette or a CD, you'd still
>  > > choose the CD, wouldn't you? There's no comparison in terms of S/N or
>  > > distortion, not to mention wow and flutter.
>  > >
>  > >> On 27 Jan 2016, at 11:17, Chris Juried <cjuried at yahoo.com> wrote:
>  > >>
>  > >> Hi Aaron,
>  > >>
>  > >> Are your preferences based on degradation of stated media and/or
>  > >> accurate reproduction of the original waveform?
>  > >>
>  > >> Sincerely,
>  > >>
>  > >> Chris Juried
>  > >> Audio Engineering Society (AES) Member
>  > >> InfoComm-Recognized AV Technologist
>  > >> http://www.JuriedEngineering.com (Juried Engineering, LLC.)
>  > >> http://www.TubeEquipment.com (Tube Equipment Corporation)
>  > >> http://www.HistoryOfRecording.com (History of Recording)
>  > >>
>  > >> This e-mail, and any attachments thereto, is intended only for use by
>  > >> the addressee(s) named herein and may contain legally privileged and/or
>  > >> confidential information. If you are not the intended recipient of this
>  > >> e-mail, you are hereby notified that any distribution or copying of this
>  > >> email, and any attachments thereto, is strictly prohibited. If you have
>  > >> received this email in error, please immediately notify me and
>  > >> permanently delete the original and any copy of any e-mail and any
>  > >> printout thereof.
>  > >>
>  > >>
>  > >>
>  > >> From: "Lanterman, Aaron" <lanterma at ece.gatech.edu>
>  > >> To: synth-diy List <synth-diy at dropmix.xs4all.nl>
>  > >> Sent: Sunday, January 24, 2016 4:38 PM
>  > >> Subject: [sdiy] "Digital vs analog waveforms" [was: Ways for innovation]
>  > >>
>  > >>> On Jan 22, 2016, at 10:27 AM, spivkurl at wearerecords.com wrote:
>  > >>>
>  > >>> they express their unfounded claims about how a digital waveform is
>  > >>> that same or "higher resolution" (uh I hate that) than an analog
>  > >>> waveform…
>  > >>
>  > >> I must once again remind cite the Nyquist-Shannon sampling theorem:
>  > >>
>  > >> https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem
>  > >>
>  > >> When you’re listening to a “digital waveform,” by that point it’s been
>  > >> converted back to analog. Analog and digital transmission and storage
>  > >> formats have different strengths and weaknesses. Analog formats tend to
>  > >> degrade gracefully; digital formats have a sharp degradation curve, in
>  > >> which they’re perfect until they’re garbage (as I’ve learned going
>  > >> through archiving some old DAT tapes). Digital waveforms are converted
>  > >> to “analog” for transmission — the cable your internet service uses
>  > >> doesn’t know anything about “bits,” but the circuits encoding and
>  > >> decoding those bits do.
>  > >>
>  > >> I’ll take a “digital waveform” off of high-rate AAC file or a CD over an
>  > >> analog waveform off my old consumer cassette tapes.
>  > >>
>  > >> - Aaron
>  > >>
>  > >>
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