[sdiy] Patchable polyphonic synth with FM or AM transmission idea

Dave dlmanley at sonic.net
Sun Dec 30 20:34:16 CET 2018



On December 28, 2018 6:05:56 PM PST, rsdio at audiobanshee.com wrote:
>I doubt that you could get analog signals to work properly over fiber
>without using frequency modulation to remove the amplitude sensitivity.

Old school analog cable TV modulates hundreds of analog RF channels for transmission over coax.  Today, single mode digital fiber is often used for delivery of digital bandwidth to homes (FTTH, GPON, EPON, etc) at distances reaching 10 to 40 kft.  In some networks they overlay the analog RF on the same fiber with the digital so everything is done over fiber, getting rid of the copper.   This technology is called RFoG, or RF over  Glass. This is done because it is a cheap way to transport the broadcast channels, leaving the digital bw for voice, data,  and video on demand. 

So yes, analog is transmitted over fiber. 

The head-end equipment is not cheap, but it is shared across 100s of houses and they're paying $$ per month for the service so there is a viable business model in urban areas. 

Not that any of this makes any senses for a synth. 

These same telecom markets are also looking at WDM, for use in distributing multiple 10Gbps streams over different lambdas (XGPON).  The optic transceivers required are expensive and only make sense when amortized across hundred of homes over years of payments. 

FDM was used for multiplexing 24, 48, 96, etc+ telephone channels over long-distance microwave links (some of this may still be deployed,  haven't looked at this in years).

Perhaps you could look at PAM. Older telephone switches would use this on the backplane to route between line cards in the pre-PCM/TDM days when ADC/DAC was expensive. 

-Dave




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