Archive for Tech

Keyboard tinkering

As I mention elsewhere in the pages I’ve been playing keyboards on and off for over 30 years now, a passion that came about from being interested in electronics and computers first, then wondering how to make music with them second.

So anything that combines the two is bound to be a bit of fun in my book.  I did just that this morning and thought would post what I learned along the way – might be of interest to others and I’ll know where to find it too :)

Back in about ’87 or ’88 I had a keyboard rig that used two Yamaha KX-76 controller keyboards – for anyone unfamilar these are keyboards that just produce a MIDI data stream that in turn goes into some other device to create the actual sounds.  To this day I’ve still got the two KXs and consider them one of the better feeling “synth action” keybeds out there.  A little noisy acoustically – so perhaps not ideal in a studio setting, but for band work ideal.  In any case, I digress…

Like most keyboards the KX-76s are velocity sensitive – the harder/faster you press, the louder the sound.  Velocity sensitivity is generated by firmware in the keyboard by working out how quickly the key has been pressed.  In practice this is usually accomplished by each key having a pair of switches (or a single leaf style switch with two positions as is the case in the KXs) that are set up so they change state one after the other as the key moves.  Time how long it is between the first one switching and the second one and you have a figure that can be turned into velocity.

The above is all stuff I’ve understood intuitively for some time, but I’ve often wondered just how quick this time interval between the two switches is – one day I’d like to build a controller of my own and this is a fairly important design consideration.  So this morning with a bit of tinkering around I was able to do some experiments to find this out – hence the setup in the photo above.

Turns out the shortest interval is around 5ms up to 20ms+ for a very slowly played key.  Anything over about 10ms seemed to be interpreted as the “minimum” velocity of (0x01).  I couldn’t manage an interval of less than 5ms or so – this corresponded to a velocity of 105 which is the maximum a KX-76 will send anyway (this a throwback to limitations of the original DX-7 as I recall which also stopped short of the 127 maximum velocity).  Also a fair bit of “keybounce” for a ms or so after contact close/open.

Key up time was 9ms if the key was allowed to return to it’s original position via the spring.

Screen capture below is typical for a mid-velocity press.

PRINT_02

One other detail I should add – the keyboard in the KX-76 is a matrix with notes as columns and octaves as rows.  It’s scanned by the microcontroller on the main board such that each note is checked once per millisecond. The scanning appears to stop until the key down time is captured, then continues.

Oh and yes, the KX-76 survived the ordeal of being poked and prodded :)

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Which Tablet should I buy ?

A dear friend recently asked for some suggestions about buying a tablet for her partner.  She wrote in part “…He travels a lot so I want him to be able to read papers, mags, books, FB, YouTube… He has WiFi and I guess all airports and hotels have it too…” – pretty standard requirements. As it happens I do have some thoughts on the topic, but figured would make it a more general post in the hope it might be of use to others :)

It’s pretty much a two horse race – you get an iPad of some persuasion or something running Android.  With the former your only choice, for better or worse is Apple, for the latter there are any number of manufacturers, personally I’d be looking at Google, Samsung, LG or Sony.

Which horse to back – in my view it’s simple – if you are at all interested in creating music or multimedia content (as distinct from just listening to or watching it) – get an iPad.  At the time of writing, alas, Android simply does not have good enough (read: any) support for low latency audio or MIDI – this is the technical underpinning required to allow a tablet to function as a musical instrument you can play in real time or “live”  It’s the only reason I have an iPad instead of an Android tablet – the musical apps are excellent – to the point where I could play a gig using just sounds from one if there was a need to (with an external keyboard and amplifier of course!)  If your entire house is already Apple-centric – buy an iPad.

If music/video content creation isn’t a serious need, then any of the recent offerings from Google, Samsung, LG or Sony are worth a look.  It’s an insanely fast moving market, but today Samsung and Google (who have their hardware made by 3rd parties anyway) look pretty good.  One of many recent reviews that discusses the current crop can be found here.

Other things to consider ?

  • I really like having built in 3G/4G for the convenience, despite the fact I basically always have a phone with me that I could tether to.  It’s just so convenient to have it work straight away, and all sensible devices still fall back to WiFi if it’s available.
    • I choose, with some philosophical reluctance to use Telstra in my iPad – they have the best but most expensive network. For my usage it works out ok and I’ve got Optus in my mobile phone which sorta offsets the cost.
  • Storage capacity – 16GB will probably suit most people unless you’re gonna want to have lots of video on there, in which case go 32GB or 64GB.  If it’s mostly music and magazines, 16GB is probably ok. If it’s for a teenager, 32GB minimum.
  • Buy a cover, ideally one that flips over to protect the screen
  • Buy a screen protector too…

It’s a bit of a buyers market at the moment, you won’t go far wrong with offerings from any of the known brands and as always, Google is an excellent resource for getting reviews on specific models.

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