2019-12-03

Bluetooth audio latency, codecs, when does it matter

These are some random-ish observations regarding Bluetooth audio latency vs "codecs". This started life as a long comment trying to untangle a messy thread in Wirecutter's review of bluetooth speakers, but since it covers a lot of things that I periodically forget about, I'll have it now as a refresher for myself next time I'm checking BT headphones.

A couple of pre-clarifications:
  • Different people measure different things, sometimes without even realizing, so it's important to make sure that one understands what a number means. Algorithmic delay? Hardware (+firmware) implementation? Hardware + software? Which software: OS + encoding + decoding, or just the OS piping things around? Is there some app involved? Each layer not only adds delay (lag, latency), but also variation (jitter).

2018-08-20

YOU could have invented the LMAX Disruptor... if only you were limited enough!

This is about a shocking realization I got while learning about the LMAX Disruptor – a data structure / architecture that got published in 2011 and made some waves across the web because it allowed LMAX to process +6M transactions per second on a single thread. In Java. Which was interesting because Java was (still?) supposed to be too slow for that kind of thing.

By then I was already a couple of years out of the Java world and getting into embedded C, so I took a mental note to look into it just out of curiosity. But, as could be expected, the note was promptly forgotten.

I'm now looking again into Java, so finally I managed to take a peek at the Disruptor. Shock: this is just a description of what I was implementing in C while I was still learning it! But it's not that I'm a genius; it's that this is probably the only way to do things when in a limited environment. In fact, the basic architecture is the one used typically in drivers and in Linux's NAPI network architecture, which is in place since the early 00's. I see a handful of others across the web having commented as much during these years.

So... is THIS what merited such coverage, talks in conferences, etc?

I used to think that a surprising part of the embedded people I've met are typically rather short-sighted and closed minded about their part of the stack; now it's looking like the higher levels are also equivalently blindsided. So it sounds like there really is a need for some condensing view, some whole-picture consideration in the industry. But, how? Who?

I guess I could take this as a job opportunity :P, but it rather sounds depressing / worrying. If computing is akin to thinking... what does it say if we programmers seemingly are such poor thinkers? And I think that "specialization" would be a really poor excuse here. "Specialization is for insects" – right? Sounds to me more like oblivious churning out. Which might be well and good when making another templated website, but not as good when writing software to control, say, medical equipment.

So let's try to analyze how and why the Disruptor is or isn't interesting, and the implications.

2018-05-23

Macbook 2013 vs 80 MHz WiFi channels

I found that the WiFi on my MacBook Pro (late-2013) works slowly on 5 GHz / 80 MHz channels (topping out at about 30 Mbps). Enough so that it's at least 3x faster when connected to the 2.4 GHz band in the same router (and I say at least because I can't measure any higher).

So, if your router works in the 2 bands and your Mac is switching between them transparently (as it usually does, which usually is advantageous), then you would be seeing big, mysterious changes in speed.

2018-03-20

CrashPlan complaints

After a couple of months using CrashPlan I wrote about its awkward feature set and their interactions. The awkwardness didn't negate that it seemed to work well enough, better than the alternatives I tried at the moment. Still, it was also bad enough that it motivated me to keep my TimeMachine local backup, even though my earlier idea was to get rid of it.

8 months later, I'm fed up enough with CrashPlan to start looking for alternatives. This is a list of my problems with it, which are the things I would have liked to realize earlier.

All of these complaints have been brought up with their Support, even explicitly as feature requests and/or bug reports, and the eventual answers have not been particularly helpful nor encouraging; in the best cases Support just provided workarounds to suspend the pain for a while.

2017-08-29

CrashPlan limitations

After a few weeks using CrashPlan PRO for small business (not the free tier!) I tried contacting support to ask how to do some underexplained things, and/or to open some bug reports/feature requests. Like:
  • How to know which were the last backed-up files? or, when was a file last backed up? (maybe some useless-but-frequently-updated file is slowing down backups of bigger and more important files?)
  • The app defines backup sets, but they don't seem to correspond to "restore sets". How to restore a particular set?
Support's answers were pretty underwhelming, bordering on canned-responses; but I found that Code42, the makers of CrashPlan, have an API to access the backup data. So I browsed a bit to see whether it'd be easy to do myself what I wanted.