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

[Chris Juried]

Hi Group,
50kHz to 100kHz is typical. It is not uncommon for bias frequencies to be as high as 150kHz, 250kHz or in the case of the Ampex ATR-100 432 kHz. It should also be noted the Wide-band Instrumentation recorders are biased around 10MHz and in some cases, higher.
 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)
http://www.linkedin.com/in/chrisjuried (LinkedIn)Email: CJuried at yahoo.com  
Voice: (954) 478-4355 


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      From: Sarah Thompson <plodger at gmail.com>
 To: Tom Wiltshire <tom at electricdruid.net> 
Cc: Chris Juried <cjuried at yahoo.com>; synth-diy List <synth-diy at dropmix.xs4all.nl>
 Sent: Thursday, January 28, 2016 10:38 AM
 Subject: Re: [sdiy] "Digital vs analog waveforms" [was: Ways for innovation]
   
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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