[sdiy] New device, weird midi behavior

rsdio at audiobanshee.com rsdio at audiobanshee.com
Wed Jan 3 00:43:07 CET 2018


On Dec 30, 2017, at 8:27 PM, Joel B <onephatcat at earthlink.net> wrote:
> On Dec 30, 2017, at 6:38 PM, rsdio at audiobanshee.com wrote:
>> On Dec 30, 2017, at 5:03 PM, Joel B <onephatcat at earthlink.net> wrote:
>>> I have this new device, a kickstarter product, it is USB Powered, and it only works well with a few of my synthesizers. For others it seems to send nothing at all, others it makes them stop making any sound at all while plugged in, as if it is sending a stream of all notes off.  In my emagic midi interface it either sends nothing, or, on another Unitor 8 in the Unitor daisy chain it sends bank select 0 every so often. Plugged into an old Opcode midi interface it seems to send proper note on off though. Seems to work ok on Roland JX8p and Yamaha tx816... not on DX7 though. Korg Minilogue but not sequential max.  Seems to send proper midi data to my iconnectMidi1 for iOS. 
>>> 
>>> Same keyboards and interfaces all respond properly to other midi sources. So I’m thinking something electrical is wrong here? 
>>> 
>>> What would you investigate to try to understand what is going on? 
>>> 
>>> Any hypotheses?
>> 
>> In other words, it's entirely possible that this Kickstarter product is not 100% USB compliant.
>> 
>> That said, your description makes it sound like you're mostly having trouble with the classic MIDI interface, so perhaps it has little or nothing to do with USB, per se.
>> 
>> As someone else pointed out, if this USB Device does not have a full 5 V boost regulator on board for the classic MIDI interface, then it may not be 100% compatible with classic MIDI devices. USB is nominally running on 5 V, but if you read the details of the spec then you'll find that a USB powered Device hanging off a bus-powered hub will only get 4.01 V, and that's perfectly legal within the USB Specifications. Unfortunately, nearly all 5 V chips require the supply to be in the range from 4.75 V to 5.25 V, and 4.01 V is not nearly enough. Some manufacturers end up shipping devices with chips that are underpowered, while others end up shipping devices with classic MIDI ports that don't match the specifications 100%. MIDI is technically a 5 mA current loop, so the exact Voltage “shouldn’t” be important. However, the transmitter and receiver circuits both involve specific resistances that won’t produce the right 5 mA current if the Voltage isn’t 5 V.
>> 
>> So, you could have a firmware problem, an electrical problem, or one of many potential specification violations.
>> 
>> Brian Willoughby
>> Sound Consulting
> 
> Thanks Brian, I passed some of what you said on to the designer, and working with them was able to resolve connectivity issues to most but not all of my gear, by dimming the LEDs on the front panel all the way down. 
> 
> Thanks for your helpful comments.
> 
> Joel

You're welcome.

Did the designer mention whether they plan on fixing this? I suppose it may be too early in the diagnosis to say, for sure...

Brian




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