Month: October 2015

Chromecast audio first impressions

I just received my #Chromecast audio and couldn't resist trying it right away with headphones.

So it's perfectly capable of driving the 300 ohms +Sennheiser​​ HD 650.
The "High Dynamic Range" seems to produce a higher quality with these headphones, the output level also gets several dB higher when activated.
(then at the maximum level, it gives a sound pressure well above the pain threshold, with surprisingly low distortion)
Subjectively it also sounds rather good, which is not the case for every equipment with the HD 650: with its mostly neutral frequency response and low distortion it becomes a lot easier to tell the difference.

A very crude quick test via lossily compressed test samples seem to indicate the presence of some resampling artifacts on 44.1kHz content, none for 48 kHz (needs verification)

Still, it could probably serve as cheap headphones DAC / amplifier for special uses for headphones notoriously difficult to drive, replacing favorably a few smartphones or laptops' audio output.

But please don't take my word on it quite yet, I'll test with more headphones / earphones and also complete measurements.

I might have to write some new code for that however in order to cast lossless audio – apps I found so far use lossy transcoding which is not necessary.

#supercurioBlog #audio

Source post on Google+

Looking at free SSL certificates options

While letsencrypt.org is still in beta phase, is StartSSL still the best option out here?

#supercurioBlog #web #security #encryption



Let’s Encrypt
Let’s Encrypt is a free, automated, and open certificate authority brought to you by the Internet Security Research Group (ISRG). ISRG is a California public benefit corporation, and is recognized by the IRS as a tax-exempt organization under Section 501(c)(3) of the Internal Revenue Code.

Source post on Google+

I'm tagging little by little old posts to add them to the new +WordPress​​​ blog I installed on http://supercur.io

It's hard to tell for how long +Google+​​​ will stay relevant and be used.
I also found that indexing of posts being terrible overall.

A self-hosted blog however, you know it will last!
It's possible to find its content in a search engine.
It only costs a little money per year for the domain name but that's it.

Maybe because of the social media aspects and because I like my audience (you) I'm much more inclined to write things here than on a +WordPress​​​ site or app.
On +Google+​​​ I just write, publish and.. done! It's that quick and easy. And later I re-read and correct if needed, instead of proofreading too much like I do otherwise.

Auto-importing these posts (when tagged with #supercurioBlog ) might be what I need to combine spontaneity and sustainability.

Source post on Google+

Compiling Android Marshmallow #AOSP for the +Nexus​​​​ 10, awesome!

I needed just that for display calibration driver development purposes.

Thanks you very much +Dmitry Grinberg​​​​ 😃

#supercurioBlog #development



Android M on Nexus 10 – Dmitry Grinberg
How to build Android Marshmallow on Nexus 10. The story thus far… Many were very sad when google chose not to update Nexus 10 to Android 6.0 Marshmallow. This simple guide will show you how to build Android 6.0 Marshamllow for Nexus 10. And for the lazy, I also have a pre-built AOSP …

Source post on Google+

Here's the results of the current state of my display calibration algorithm on the early batch Nexus 5 I sent back and its refurbished replacement

Following up on https://plus.google.com/+supercurioFrancoisSimond/posts/cgKUgJEPTtc

On both, a 12-bit RGB LUT is loaded in hardware, but as you can see on the curves in these graphs, the panel being only 8-bit, there's some banding going on.
I started working on another driver approach that allows to avoid this 8-bit limitation and permits extremely precise correction.

The target for both is D65 white point (as seen by the sensor for simplification), gamma 2.2 curve with a fine-tuned near-black response to avoid clipping or visual artifacts in shadows and near black, also preserving the color balance as much as possible near black.

The replacement Nexus 5 stays better even when both are calibrated thanks to its higher native brightness, slightly higher contrast ratio, and better consistency in its RGB channels which requires less correction.
Although beside the brightness difference which is appreciable, they look the same.

On both, the grayscale Delta E stays below 1 which is a very good accuracy despite the current 8-bit per channel driver hardware limitation.

Subjectively, it also looks pretty darn good 🙂

Other info:

Maximum brightness – significant difference
original: 381 cd/m², replacement 474 cd/m²

Contrast ratio
original: 862:1, replacement: 891:1

On both, HCFR calculates an average gamma value of 2.18 without black point compensation and 2.21 with.

#supercurioBlog #calibration #display #color #development #measurements

              

In Album Display Measurements: my calibration algorithm on first batch Nexus vs refurbished replacement

Source post on Google+

A few days ago I sent back my Nexus 5, from the first batch shipped to France for a defect behind the glass lens

The replacement unit I received immediately seemed to have a better and brighter display, which is confirmed by the measurements graphs attached.

The replacement is brighter, with warmer white point, its RGB channels curves response are a lot closer across the board.
From comparing two phones, I can't tell if one is just better than the other or if Google improved the factory calibration process.

Neither display's white look like D65 daylight white compared to actual daylight or a reference CRT monitor (regardless of the sensor used).

Other info:

Maximum brightness – significant difference
original: 409 cd/m², replacement 510 cd/m²

Contrast ratio – about the same
original: 926:1, replacement: 952:1

Average gamma – interestingly about the same despite the difference in curves
original: 2.07, replacement: 2.08

Up next: results calibrated 😉

#supercurioBlog #calibration #display #color #measurements

         

In Album Display Measurements: first batch Nexus 5 vs refurbished replacement

Source post on Google+

There's a new revision of the popular X-Rite i1 Display Pro colorimeter out here, and the latest ArgyllCMS release is not able to drive this sensor fully yet

+Vincent Sergère is a proud owner of one and can't use it quite yet for what it's intended for now.

Hoping this message will help ArgyllCMS's author!

#supercurioBlog #development #color #calibration



[argyllcms] Error with new i1 Display Pro revision – argyllcms – FreeLists
[argyllcms] Error with new i1 Display Pro revision. From: François Simond ; To: argyllcms@xxxxxxxxxxxxx; Date: Fri, 9 Oct 2015 02:29:27 +0200. Hi Graeme and the list! I’m assisting a friend with his brand new X-Rite i1 DisplayPro, which has a new revision and firmware.

Source post on Google+

Published yesterday by +iFixit​ :Chromecast 2015 and Chromecast Audio teardowns

On the audio part, we learn about the CC Audio's DAC setup used to drive the analog output.

The stereo DAC is an AKM AK4430:
http://www.akm.com/akm/en/file/datasheet/AK4430ET.pdf
– Up to 192kHz / 24-Bit
– 128 times oversampling for 8-48 kHz, 64 times oversampling for 32-96 kHz, 32 times oversampling for 45-192 kHz.
– 2Vrms output with its own charge pump
– 104 dB Dynamic Range
– -91 dB THD+N
– -104 dB crosstalk

Those are fine specs by themselves, but Google decided to add a component in the output path, a +Texas Instruments​ DRV632 Line Driver:
http://www.ti.com/product/DRV632/technicaldocuments
http://www.ti.com/lit/ds/symlink/drv632.pdf
– 105 dB Dynamic Range / SNR
– 0.002% THD+N = -94 dB THD+N
– 2Vrms output with its own charge pump.
– -110 dB crosstalk at 1Vrms output

I'm not exactly sure why this second component is present since the DAC already outputs in 2Vrms, which is what you want for line-output
+Texas Instruments​ lists the DRV632 usages as:
– a way to adjust the output gain (but only via external resistors and not digital)
– line output protection
– short circuit protection
– DAC post-filter (typically as a low-pass)
Based on the DRV632 specs, it should not harm the audio quality.

With a current limit of 25 mA, it should also be capable of driving some small headphones (although it's not designed for that)

Measurements will tell more the actual performance of this analog combo.

About that, Google just notified me of my Chromecast audio's shipment, so I'll try just that after receiving it.

#supercurioBlog #Chromecast #audio #teardown



Chromecast 2015 Teardown – iFixit

Source post on Google+

The struggle of Discourse forum software authors is real

Discourse is pretty great:
– works as forum as well as a mailing list
– the mobile version is highly usable, reading threads is a comfortable experience.
– search is powerful and efficient
– designed to facilitate community management and moderation
– on the server side, it's easy to update

However the stack choice: Ember.js Javascript framework client-side, Ruby on Rails server-side with most of the work done client-side has been giving satisfying performance only on desktop and iOS with Safari.

On everything else: Android devices (Chrome and Firefox), Windows Phone, Firefox OS, you name it: the initial page loading time is slow enough so that each time, compared to another website you start to wonder if the website froze, your Internet connection dropped or who knows what.
And there's no loading progress indicating that something is happening.

Once the forum Javascript software and state of things are loaded in your tab things are fast enough.

The software authors have since the beginning take as reference iPhone's Javascript performance for this framework, and speculated that every other smartphone out here would follow the same performance gains with time.

The problem is that Apple's Nitro Javascript VM is the only one able to optimize this framework's code, and that the trend is that the volume of new smartphone owners, especially in the regions where websites are preferred to apps are getting equipped with inexpensive devices with small cores, definitely not running iOS.

Sometimes you don't bet on the right software stack for your need and it's a painful realization.
This thread is a example of that, and you see plenty of denial, blame shifting and other defense mechanisms going on.

They might still get away with it with a work-around making the initial page load and display much faster thanks to server-side rendering tho. And loading all the heavy stuff once the content is already visible.

#supercurioBlog



The State of JavaScript on Android in 2015 is… poor – Discourse Meta

Source post on Google+

A few small errors in comparisons methods, like:

– Comparing still images at 100% zoom for different sensor resolutions instead of normalized resolutions.
– Comparing still images taken at a different focal length / field of view.

But still an interesting video from +SuperSaf TV!
The +Sony Xperia Z5 does a good job at stabilization, especially in 1080p video.
It's a shame that 4K video recording doesn't benefit from the same stabilization quality, although there's still some.
As it's digital stabilization only however, you'll often see some artifacts coming from the motion blur due to movement in frames.

The Z5 also does a good job at stabilizing the front facing camera although it's at the expense of some artifacts and crop, is there no such capability on the Galaxy S6?

Galaxy S6 front and back lens are very good at dealing with flare, which is not the case with the Z5.

The Z5 color profile and automatic white balance is colder, as usual with +Sony products.

Galaxy S6 appears to be more reliable and consistent overall than the Z5, which can sometimes get the automatic white balance all wrong like at 4:57 (it gets a nuance of green as white reference, hence the whole scene turning into almost greyscale)

#supercurioBlog #camera #color #comparison

Source post on Google+