Become a Site Supporter and Never see Ads again!

Author Topic: Multichannel multiplexing for stereo recorders  (Read 467 times)

0 Members and 1 Guest are viewing this topic.

Offline ~Jon Stoppable

  • Trade Count: (46)
  • Needs to get out more...
  • *****
  • Posts: 3155
  • Gender: Male
    • Naiant Studio
Multichannel multiplexing for stereo recorders
« on: January 04, 2017, 05:04:59 PM »
From here:

http://taperssection.com/index.php?topic=180460.msg2212675#msg2212675

I have a sketch of a 4x2 mux with PIP input, but I was kinda waiting on a promised newer DSP chip before I pulled the trigger on the design.  That might be later this year.  It wouldn't be much of a change to do 4x1 and use two of those, so long as the receiving recorder actually has about 88kHz bandwidth at 192kHz.

Very interesting.  Possible  4X2 (44.1kHz > 96kHz) option?  That would broaden the field of perspective recorders significantly.  All the Sony M10s around here would become 4ch capable, the Tascam Dr2ds 8ch capable.  Will keep my ears open.

Sure, obviously 4x2 is easier than 4x1.  Probably worth checking to see if they actually have 44kHz bandwidth.  I have an eval kit for a DSP chip that could be used for proof-of-concept, but its power consumption is rather appalling for field use.

The trick of course is demodulating, you'd need a plugin programmed to do that.  I could code the basics of demodulation but the tricky part is writing a PLL that locks onto the carrier.  I dunno how to code PLLs, but somebody out there does.  I would do it the dummy's method of a manual tuning control.  That works so long as the carrier tone doesn't modulate (it shoudn't).  But for a lot of applications the typical crystal tolerance is probably good enough.  It would certainly be better than just about any cassette tape.  Or maybe there is a precoded PLL block that would do it for me (it's been a lot of years since I had time to play with coding VSTs).

This is a fun read, the spacing could be a bit tighter with digital filters, especially since you don't really need dual sidebands:

https://en.wikipedia.org/wiki/FM_broadcasting#Quadraphonic_FM

Offline Gutbucket

  • record > listen > revise technique
  • Trade Count: (12)
  • Needs to get out more...
  • *****
  • Posts: 10989
  • Gender: Male
Re: Multichannel multiplexing for stereo recorders
« Reply #1 on: January 04, 2017, 06:52:55 PM »
Interesting stuff.

Sort of a complex work around for squeezing extra channels in, yet doable. Better than having to run two recorders and syncing files afterwards. I should check the real-world bandwidth though the DR2d recorders I've been using.  Have you done that with any of the common small 2 channel recorders? I remember you mentioning less than stellar real world dynamic range figures for many of the recorders in this class at some point.

Will be interested in what you learn in messing around with that DSP eval kit.
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

"Narrow or widely spaced microphone configurations are preferred. It is well-known experience that pure coincidence microphone concepts are not able to produce a satisfying natural spatial impression, due to the lack of adequate interchannel temporal relations (time-of-arrival, phase, correlation)" -G√ľnther Theile
"The mix of the Double M/S signals with a large A/B configuration of omnis results in the spacious sound that is often desired. This option also provides decorrelated low-frequency signals." -Helmut Wittek

Offline ~Jon Stoppable

  • Trade Count: (46)
  • Needs to get out more...
  • *****
  • Posts: 3155
  • Gender: Male
    • Naiant Studio
Re: Multichannel multiplexing for stereo recorders
« Reply #2 on: January 04, 2017, 07:02:56 PM »
Dynamic range doesn't matter too much for this purpose though, just bandwidth.  Bandwidth should just be a function of sample rate, but it's not impossible that a portable recorder would have some sort of bandwidth limitation in its own DSP.

 

RSS | Mobile
Page created in 0.096 seconds with 29 queries.
© 2002-2017 Taperssection.com
Powered by SMF
Website Design by Foxtrot Media, Inc., a Baltimore Website Company