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

[Simon Brouwer]

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)
> >>
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> >>
> >> 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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