[sdiy] Digital modular backplane - update

Mon Mar 31 11:16:22 CEST 2014

hi, and welcome!

I'm wondering why you didn't mention anything about "Brain Controlled 
MIDI", which seems obvious project for you. I bet you have working 
prototype hidden somewhere in a drawer... Please show us!
I'd be surely interested in that. But sorry, don't expect a job position 
from me, can't afford an emplloee at Dutch level of sallary yet ;)

Roman

W dniu 2014-03-30 20:06, Rutger Vlek pisze:
> Hi Damian,
>
> Thanks for collecting and sending all the info! Looks great. I am a
> list member for quite some time already, but have become more
> "active" in the last months. Here's a brief introduction for anyone
> interested:
>
> My name is Rutger, 31 y/o, living in Nijmegen (Netherlands). Have
> been playing keys for various (prog) rock bands and doing synth DIY
> since age of 21. Have a masters degree in artificial intelligence and
> just finished a PhD in Brain-Computer Interfacing (with EEG). Looking
> for job opportunities to move away from academia. I love science, but
> I hate present academic climate (pressure, ego's, competition, etc).
> Thinking about starting a small company to share some of my recent
> DIY efforts with a wider audience. Have recently been working on
> prototyping a new idea for a discrete OTA and obtained pretty good
> results! Also very much interested in the "bigger picture" of synths
> and other new instruments, large innovations, a new standard to
> replace MIDI, digital modulars, etc :).
>
> Best,
>
> Rutger
>
> ps. And did already mention that I'm looking for job opportunities in
> synth design (sorry, shameless pluggin' going on here).
>
>
>
>
>
>
>
>
> On 30 mrt 2014, at 15:27, cheater00 . wrote:
>
>> Hi John and Rutger, thanks for your emails. First of all, welcome
>> to the list - I have not spoken with you before, and I guess this
>> is one of the first posts for each of you.
>>
>> I am guessing you don't recollect, or haven't been involved with,
>> the original conversation from November 2013. I have had to ask
>> Paul for permission, but I have now forwarded the whole original
>> thread to the list. The thread is not all in the synth-diy archive,
>> which is troubling.
>>
>>
>> On Thu, Mar 20, 2014 at 4:00 AM, john slee
>> <indigoid at oldcorollas.org> wrote:
>>> Hi,
>>>
>>> On 17 March 2014 22:24, cheater00 . <cheater00 at gmail.com> wrote:
>>>> Some time ago we have spoken about what it would take to make
>>>> a digital backplane for a modular synth.
>>>
>>> What problem is this attempting to solve? Being able to save
>>> signal routing and control state in a patch would be nice, I
>>> suppose, but
>>>
>>> - physical settings != patch settings => replace controls with
>>> "soft equivalents" => encoders/momentaries => current state no
>>> longer obvious => more indicator lights etc => may require more
>>> front panel real estate than "real" controls => more $$$
>>>
>>> What other benefits of going all modern do you see?
>>>
>>> John
>>
>> The basic idea (which you will find more details on in the
>> original thread I have just forwarded) is that you use analog
>> modules. Those modules are connected via digital patch cables. Much
>> like Rutger suggests below...
>>
>>
>> On Sat, Mar 22, 2014 at 12:05 PM, Rutger Vlek
>> <rutgervlek at gmail.com> wrote:
>>> I've been thinking about the concept of digital modulars too, but
>>> I think that until digital technology advances much further
>>> (lower latency, higher sampling rate, more CPU power, high bus
>>> speeds) the key differences between analog and digital domains
>>> will limit the usefulness of a 'digital modular' approach. Some
>>> things sound better, and are more cost effective, in the analog
>>> domain: such as oscillators and filters with lots of character, a
>>> little bit of drifting, etc. And some things sound better, or are
>>> more cost effective in digital: noise properties, patch storage,
>>> complex connections that would otherwise require lots of messy
>>> cables.
>>
>>
>> ...the idea is to take the best of analog, and the best of
>> digital. Analog is obviously better at generating and processing
>> sound. Digital is better at moving it around, meaning recording and
>> playback. Michael Jackson's album Thriller was multitracked in
>> digital.
>>
>> My latest update, which I again include below (as it's been 10
>> days and many readers have likely deleted the original post), talks
>> about a possibility of realizing a modular bus for hauling a lot of
>> audio around in digital with as little latency as possible. Ideally
>> the latency should be as much as it takes to digitize a single bit
>> of signal, send that single bit, and then reproduce it with a DAC.
>> This should make even feedback topologies useful.
>>
>> Naturally, for situations where feedback isn't good in digital,
>> front-panel patch points should still be available.
>>
>> Cheers, Damian
>>
>> On Mon, Mar 17, 2014 at 12:24 PM, cheater00 . <cheater00 at gmail.com>
>> wrote:
>>> Hi guys, Some time ago we have spoken about what it would take to
>>> make a digital backplane for a modular synth. One of the issues
>>> was that most common digital interconnects will introduce large
>>> delays in transporting the audio which are not acceptable in
>>> modular synthesis. A requirement was mentioned of ideally having
>>> the delay as low as the transmission time of 1 bit. This has to
>>> take into account the situation that an ADC or DAC will operate
>>> at low clock speeds, while the backplane would operate at very
>>> high clock rates, in order to accomodate many ADC-DAC links in
>>> the switched, TDM fabric.
>>>
>>> I have come across the idea of using a SerDes:
>>>
>>> http://en.wikipedia.org/wiki/SerDes
>>>
>>> They are basically shift registers with additional ISO OSI Layer
>>> 1 processing. in specific, it seems a popular type uses 8b/10b
>>> encoding which limits the RFI impact, and makes the layout much
>>> easier as the lower bandwidth limit of the physical links goes
>>> further up, while the upper bandwidth limit doesn't move.
>>>
>>> In addition this device family addresses the issue of having
>>> slow links on fast backplanes:
>>>
>>> "Bit interleaved SerDes multiplexes several slower serial data
>>> streams into faster serial streams, and the receiver
>>> demultiplexes the faster bit streams back to slower streams."
>>>
>>> It seems in this case there is no bunching or buffering so the
>>> latency can be kept to a minimum.
>>>
>>> Silicon for SerDes applications exists and is popularly used in
>>> loads of consumer technologies:
>>>
>>> "Among the areas in which 8b/10b encoding finds application are
>>> the following:
>>>
>>> PCI Express at speeds below 8.0 GT/s IEEE 1394b Serial ATA SAS
>>> Fibre Channel SSA Gigabit Ethernet (except for the twisted pair
>>> based 1000Base-T) InfiniBand XAUI Serial RapidIO DVB Asynchronous
>>> Serial Interface (ASI) DisplayPort Main Link DVI and HDMI Video
>>> Island (transition-minimized differential signaling)
>>> HyperTransport Common Public Radio Interface (CPRI) OBSAI RP3
>>> interface USB 3.0 CoaXPress MIPI M-PHY[6] ServerNet (From
>>> ServerNet2 onward)"
>>>
>>> It might be possible to find switched fabric chips that can route
>>> the links on an X/Y grid for best bandwidth utilization, and
>>> which can do so without buffering. At least that is what I would
>>> expect of what Infiniband, Gb Ethernet, and Fibre Channel are
>>> doing.
>>>
>>> Cheers, D.
>
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