The modern web<\/a> is unbearable without a good ad-blocker such as\nuBlock Origin<\/a>. Unfortunately, the online marketing\nindustry, while destroying the web, providing creative\ndistribution networks for malware<\/a> and disinformation<\/a>\ncampaigns there \u2026<\/p>","content":" This article describes an approach to blocking ads in audio\nfiles and introduces software that implements it.<\/p>\n The modern web<\/a> is unbearable without a good ad-blocker such as\nuBlock Origin<\/a>. Unfortunately, the online marketing\nindustry, while destroying the web, providing creative\ndistribution networks for malware<\/a> and disinformation<\/a>\ncampaigns there, has also discovered podcasts<\/a> as a\nmedium for spreading obnoxious advertisements.<\/p>\n Since podcasts<\/a> (also known as audiocasts) usually\nintegrate advertisement clips inline as part of the audio stream\nin the audio file such that they can't simply be filtered by\nblocking certain URLs or manipulating scripts, as it's done with\nads on websites or even Youtube. (NB: as of 2024, Youtube is\nexperimenting<\/a> rendering ads server-side into the\nvideo-stream)<\/p>\n However, many podcasts, especially German ones, clearly mark the\nbeginning and the end of an advertisement by some sound bite or\njingle.\nSuch marking isn't entirely voluntarily, because a few\nlegal norms regarding broadcasting<\/a> and unfair business practices\ndo apply<\/a>.<\/p>\n One approach to blocking audio ads in podcasts is thus to\nautomatically search for the characteristic samples (templates)\nand cut everything in between out.<\/p>\n I searched for software that implements this approach, but couldn't\nfind any.<\/p>\n Thus, I created cutbynoise<\/a> - a small Python program that cuts\naudio files by characteristic templates. \nSee also its README for a detailed technical description of how it works.<\/p>\n Of course, nobody wants to manually call Using cross-correlation<\/a> to search for ad start\/stop markers works\nsurprisingly well on real world audio data.\nEspecially given that podcasts are usually heavily post-processed\nand of course lossily compressed.<\/p>\n I'm running castproxy and cutbynoise for two months now on a\ndozen or so podcasts.<\/p>\n So far this setup successfully filtered out 5301 seconds of super\nannoying ads! Almost one and a half hours!<\/p>","category":[{"@attributes":{"term":"misc"}},{"@attributes":{"term":"adblocking"}},{"@attributes":{"term":"podcast"}},{"@attributes":{"term":"audiocast"}},{"@attributes":{"term":"audio"}},{"@attributes":{"term":"signal-processing"}}]},{"title":"Shift Typing","link":{"@attributes":{"href":"https:\/\/gms.tf\/shift-typing.html","rel":"alternate"}},"published":"2023-10-07T18:00:00+02:00","updated":"2023-10-07T18:00:00+02:00","author":{"name":"Georg Sauthoff"},"id":"tag:gms.tf,2023-10-07:\/shift-typing.html","summary":" This article introduces shift-tutor<\/a>, a Linux program that filters\nshift key events to improve or verify touch typing skills.<\/p>\n Most keyboards contain two shift keys, i.e. one located on the\nleft bottom and the other on the opposite side:<\/p>\n This article introduces shift-tutor<\/a>, a Linux program that filters\nshift key events to improve or verify touch typing skills.<\/p>\n Most keyboards contain two shift keys, i.e. one located on the\nleft bottom and the other on the opposite side:<\/p>\n The purpose of these arguably redundant keys is to simplify\nshifting while touch typing<\/a>. For example, when typing an upper\ncase 'A' the left hand should press the 'A' key with the little finger, i.e.\nwhich doesn't leave the home row, while the right hand is free\nand thus its little finger can easily leave the home row and press\nand hold the right shift key, before.<\/p>\n A typist unskilled in touch typing may be tempted to enter upper\ncase characters with one hand, like a short cut that involves a\nsingular meta key. In our example, this may lead to upper case\n'A' being entered by pressing left shift with the left little \nfinger together with 'A' being pressed by the left ring finger.<\/p>\n When touch typing, underutilizing both available shift keys may\nlead to the following problems:<\/p>\n When attending an on-site course in a touch typing school, a good\nteacher may be able to observe suboptimal usage combinations of\nthe shift keys and give immediate feedback such that this bad habit\nis eliminated.<\/p>\n This is similar to a presentation coach who watches out for filler words,\nperhaps rings a bell when a filler is uttered and\/or counts them such that\nthe student can pay into a filler word piggy bank.<\/p>\n In other words, in these cases, a teacher supervises a student\nand gives immediate feedback to reinforce optimal behaviour in\norder to improve the learning outcome.<\/p>\n Shift-tutor<\/a> is a technical aid that can be used while\nlearning touch typing or for verifying touch typing skills. It\nsimply grabs all events of a keyboard device on Linux and filters\n(i.e. discards) key presses whenever the wrong<\/em> shift key is\npressed. All other events are simply forwarded.<\/p>\n In that way, the typist gets immediate feedback on shift key\nusage, i.e. since something like Shift-tutor is written in Python, doesn't require much code and\nis arguably easy to extend. Thus, triggering some annoying bell\nwhenever a suboptimal key combination is pressed (in addition to\ndiscarding it), like in a positive punishment operant\nconditioning<\/a> scheme is left as an exercise to the reader.<\/p>\n Since keyboard events are filtered in user-space, such filtering\nas implemented by shift-tutor increases input latency somewhat.\nThat means in the best case shift-tutor requires 2\nkernel-\/user-space transitions and a few cycles in user space\nwhich adds a few microseconds or so.<\/p>\n Depending on the load and available cores, waking up\nshift-tutor might even require a more expensive rescheduling or\ncontext-switching that would increase the latency more.<\/p>\n However, over the years local input-to-display latency\nincreased to the three digit millisecond range<\/a> with\nmodern computers and modern keyboards being in the two digit\nmillisecond range<\/a> already (see also R. Wimmer, A. Schmid,\nand F. Bockes: On the Latency of USB-Connected Input Devices. ACM CHI\n2019<\/a> and S. Liu, and M. Claypool: EvLag - A tool for\nMonitoring and Lagging Linux Input Devices. ACM MMSys\n2021<\/a>). Recently, I was in the market for a Class-D<\/a> amplifier\nto replace an aging model. This article reviews the very compact\nFosi Audio TSA7498E 2 channel amplifier<\/a> I bought from a China\nbased business, via Amazon. tl;dr: Can't recommend, use something\nbetter.<\/p>\n Recently, I was in the market for a Class-D<\/a> amplifier\nto replace an aging model. This article reviews the very compact\nFosi Audio TSA7498E 2 channel amplifier<\/a> I bought from a China\nbased business, via Amazon. tl;dr: Can't recommend, use something\nbetter.<\/p>\n I needed a small and efficient amplifier for connecting a pair\nof old 4 Ohm monitor boxes (JBL Control One) to a computer.\nClass-D<\/a> amplifiers are known to be much more power\nefficient than traditional Class-AB ones. For example, I measured\nan old Class-AB Pioneer A-109 stereo amplifier at 33 W, during\nidle. That means that energy is wasted in the form of heat, which\nmight be especially annoying in the summer.\nWhereas a comparable Class-D amplifier just consumes a few watts, and\nlikely completely shuts down during idle operation.<\/p>\n Unfortunately, Class-D amplifiers often aren't clearly marketed\nas such and thus kind of hard to select for when browsing Hi-Fi\nvendor's product pages. Also, some Hi-Fi vendors just use Class-D\nfor very large amplifiers, where Class-AB simply gets impractical\nand only have Class-AB for living room amplifiers.<\/p>\n The best bet is to look at the power consumption ratings,\nif available.<\/p>\n When searching for Class-D amplifiers on Amazon the results are\nflooded with Chinese products, i.e. distributed by some no-name\nsmall companies, which probably are renamed often, whose wares\nare shipped from Amazon warehouses, without much quality control.\nJudging from the product images, many products from different\nvendors look quite similar to each other, i.e. it seems different\nvendors are just reselling wares from the same manufacturer.<\/p>\n I bought the Fosi Audio TDA7498E 2 channel amplifier because its\ndesign is minimal and compact and it isn't too expensive.\nAlso its reviews are quite positive, however nowadays Amazon is\nalso flooded with paid and low-quality reviews, so this has to be\ntaken with a grain of salt.<\/p>\n The Fosi Audio TDA7498E indeed is very compact and has a low\npower consumption. On idle I measured 0 W or so and during real\nuse I never measured above 1 W power.<\/p>\n Except for the volume knob, the design is nice, i.e. it comes in\na full metal case and with dual-use speaker connectors,\ni.e. one can connect speakers with banana plugs or raw cables.\nHowever, the volume knob isn't marked and way to easy to turn,\ni.e. it's very easy to turn it by accident to some high level.\nThis is especially problematic because the useful range for\nliving room volume levels is tiny, i.e. a few millimeter turn\nalready leads to a high volume. Last, it comes with a real power\nswitch.<\/p>\n At least when connecting 4 Ohm speakers, the amplifier creates a\ntoo high amount of background noise.\nProbably all amplifier speaker combinations produce some\nbackground noise, but usually it's only audible if you place one\near just a few centimeters from the speaker (while playing\nsilence and turning the volume knob up). With the Fosi Audio\nTDA7498E amplifier the background noise is still audible in a few\nmeters distance, which makes it unsuitable for office usage.<\/p>\n There is a channel imbalance at living room volumes, i.e. below\n30 dB or so, of plus 6 dB on the left, when using audio sources\nwith standard line-out levels.\nThat means one either has to compensate that amount by adjusting\nthe line-out balance settings of the connected audio source (if even\npossible). Alternatively, one might reduce the audio source's\nline-out level to 72 % or so and turn up Fosi Audio TDA7498E's volume accordingly.<\/p>\n Both workarounds are ridiculous, i.e. one simply doesn't\nartificially decrease the quality of the input signal to work\naround channel imbalance in the amplifier.<\/p>\n Last, the speaker polarity on both channels is reversed, i.e.\nblack is positive and red is negative. Granted, it would be worse\nif just one channel was reversed (cf. phase shift), but\nstill, this speaks volumes regarding the quality of the product.<\/p>\n My hearing is better than I thought. That means I immediately\nnoticed the channel imbalance and background noise. Furthermore,\nthe compensation levels and range (where the imbalance occurs) I\nsubjectively determined by changing mixer knobs until I didn't\nnotice any imbalance anymore, first while listening to normal\nmusic and then to pink noise, matched a later verification with a\nsound-level meter<\/a> pretty well.<\/p>\n The alsa-utils package contains the FWIW, I also was able to detect a defect speaker with speaker-test,\nwhere its deficiencies were more obvious.<\/p>\n In case no dedicated sound-level meter is available, depending on\nyour smartphone, a sound-level measuring app might be good enough\nfor speaker balance testing (see<\/a> also<\/a>). FWIW, I\ntested the Google Pixel 6a with the 'Noise Meter' Android app and\nobserved reasonable performance. However, as of the end of 2022,\nthe 'Noise Meter' app seems to have vanished from the Google play\nstore, as well as the company behind it (JINASYS) seems to have\nvanished from the internet.<\/p>\n As mentioned previously, the Amazon Reviews for the Fosi Audio\nTDA7498E<\/a> amplifier are quite positive, i.e. as of 2022-12-31 it has\nan average rating of 4.3 on a five star scale with 63 % 5 star\nand 19 % 4 star ratings.<\/p>\n Especially in the last years, Amazon is plagued more and more \nwith fake reviews and reportedly doesn't police enough against\nthem. Thus, some of those positive reviews might be fake, either\ngenerated by some 'AI' bots or by some incentivised persons.<\/p>\n However, many of the positive Amazon reviews may very well still\nbe genuine. This can be explained by various factors such as:<\/p>\n Mini or micro stereo systems are an alternative to a dedicated\namplifier, because they are widely available and tested by\nreputable independent entities. For example, in Germany there is\nthe independent Stiftung Warentest<\/a> consumer organisation\nwhich tests this product group periodically. Their last tests\ninclude power ratings, besides the usual feature comparisons,\nsuch that selecting systems with Class-D amplifiers (and other\nrequired features) is much simpler than having to research all\nsuch details on ones own.<\/p>\n I settled on an ultra compact stereo system from an established\nvendor: the Panasonic SA-PMX94 (a.k.a. SC-PMX94 or SC-PMX94EG-S\nor SC-PMX94EG-K). It comes with a pair of 3 Ohm speakers which\nare quite decent.<\/p>\n It might be even possible to connect third-party speakers to that\nsystem, possibly even 4 Ohm ones, as the conventional wisdom is that\nspeakers that exceed the amplifiers impedance rating (within reason)\nshould work while connecting lower Ohm speakers\nis considered dangerous, as they might draw too much power such\nthat the amplifier operates outside of its safe operating area\nand might get damaged. However, I'm not an electronics engineer\nand haven't tested it, so YMMV.<\/p>\n That stereo system comes with some features I don't really need,\nbut are still kind of nice to have, e.g. a DAB+ receiver and\nintegrated CD player.<\/p>\n The best thing about it, besides good sound quality (i.e.\nno excessive background noise and balanced channels!) and\na reasonable volume knob, is its connectivity. That means\nbesides Bluetooth, optical S\/PDIF (TOSLINK), standard analog-in\n(Cinch\/RCA) it also integrates a standard USB sound device!<\/p>\n In that way it is able to also replace an existing USB sound card and\npossibly a separate external DAC device. That means one can simply\nconnect the stereo system via USB to a computer and it should be\ndetected like an external USB sound card. I'm using it under\nLinux where it worked out of the box without any extra drivers.<\/p>","category":[{"@attributes":{"term":"misc"}},{"@attributes":{"term":"review"}},{"@attributes":{"term":"audio"}}]},{"title":"Scanning I2C addresses","link":{"@attributes":{"href":"https:\/\/gms.tf\/i2c-scanner.html","rel":"alternate"}},"published":"2022-09-21T16:00:00+02:00","updated":"2022-09-21T16:00:00+02:00","author":{"name":"Georg Sauthoff"},"id":"tag:gms.tf,2022-09-21:\/i2c-scanner.html","summary":" I2C<\/a> is a simple open-drain bus that is popular for\nconnecting devices to microcontrollers (MCUs)<\/a>, such as\nsensors, RTCs<\/a>, displays etc. Devices on the I2C bus are\naddressed by 7 bits and the bus data and clock lines are\npulled-up by a set of pull-up resistors. A good first test \u2026<\/p>","content":" I2C<\/a> is a simple open-drain bus that is popular for\nconnecting devices to microcontrollers (MCUs)<\/a>, such as\nsensors, RTCs<\/a>, displays etc. Devices on the I2C bus are\naddressed by 7 bits and the bus data and clock lines are\npulled-up by a set of pull-up resistors. A good first test for\nchecking that I2C communication works fine is to scan for the\ndevices' addresses. This article presents two I2C address\nscanners for ATmega328p AVR (e.g. Arduino Pro Mini 3.3V 8 MHz)\nand GD32VF103 RISC-V (e.g. Longan Nano) MCUs.<\/p>\n On an I2C bus, every communication is initiated by a master\n(controller) that addresses a slave (target) device. There can be\nmultiple controllers and multiple targets on a bus. With MCUs,\nit's common to have one controller (the MCU) and one or more\ntarget devices connected to a bus.<\/p>\n An address of a target is static, i.e. there is no address\nautoconfiguration protocol. Usually, the address of a target is\nspecified in its datasheet.<\/p>\n The following sequence diagram describes the structure of I2C\ncommunication:<\/p>\n The basic idea with I2C address scanning is to simply send\nSTART conditions for all possible addresses (there are just up to\n Of course, in any case, after sending the address and detecting either an ACK\nor NACK the controller immediately sends a STOP condition to avoid confusing\nany target device and being able to continue with the next one.<\/p>\n There are several<\/a> I2C scanners around<\/a> that use the Arduino API.\nArguably, that API hides too much of the I2C fundamentals, such\nthat it's not immediately obvious how the scanning really works.<\/p>\n I thus wrote a bare bones I2C scanner that directly interfaces\nwith the I2C unit of an 8 bit ATmega MCU using its registers:<\/p>\nMotivation¶<\/a><\/h2>\n
The Challenge¶<\/a><\/h2>\n
A Solution¶<\/a><\/h2>\n
cutbynoise<\/code> on each new\nepisode of a podcast. I thus also created castproxy<\/a> - a\nsmall Python program that aggregates podcast feeds, caches\nembedded audio files, and is able to invoke audio filters on\nthem, such as cutbynoise<\/code>.<\/p>\nResults¶<\/a><\/h2>\n
Rationale¶<\/a><\/h2>\n
![\"](\"https:\/\/gms.tf\/image\/ansi-querty-ergo-wp-commons.svg\")
\nSource: Mliu92<\/a>,\nANSI\nUS QWERTY (Windows, split + rotated)<\/a>, CC \u2026<\/a><\/small><\/p>","content":"Rationale¶<\/a><\/h2>\n
\nSource: Mliu92<\/a>,\nANSI\nUS QWERTY (Windows, split + rotated)<\/a>, CC BY-SA 4.0<\/a><\/small><\/p>\nThe Problem¶<\/a><\/h2>\n
\n
A Solution¶<\/a><\/h2>\n
Shift-Tutor¶<\/a><\/h2>\n
left_shift + a<\/code> is discarded,\nthe better usage of right_shift + a<\/code> is reinforced.<\/p>\nWhat about Latency?¶<\/a><\/h2>\n
\n
\n
\n
\n
Motivation¶<\/a><\/h2>\n
Selection¶<\/a><\/h2>\n
Review¶<\/a><\/h2>\n
The (mostly) Good¶<\/a><\/h3>\n
The Bad¶<\/a><\/h3>\n
The Ugly¶<\/a><\/h3>\n
Lessons Learned¶<\/a><\/h2>\n
speaker-test<\/code> command which\nis quite convenient for testing speakers. Example:<\/p>\n<\/span>speaker-test <\/span>-c2\n<\/code><\/pre><\/div>\n\nAmazon Reviews¶<\/a><\/h2>\n
\n
Alternatives¶<\/a><\/h2>\n
\n
\n
\n
I2C High-Level Overview¶<\/a><\/h2>\n
![\"I2C](\"https:\/\/gms.tf\/image\/i2c-sequence.svg\"\/)
<\/p>\nI2C Address Scanning¶<\/a><\/h2>\n
2^7<\/code> of them!) and detect ACKnowledgement conditions on the bus, in a loop.<\/p>\nScanning on the ATmega328p¶<\/a><\/h2>\n
<\/span>\/\/ at 8 Mhz<\/span>\nstatic<\/span> <\/span>void<\/span> <\/span>i2c_set_100kHz<\/span>()<\/span>\n{<\/span>\n <\/span>TWBR<\/span> <\/span>=<\/span> <\/span>32<\/span>;<\/span>\n}<\/span>\nstatic<\/span> <\/span>void<\/span> <\/span>i2c_set_400kHz<\/span>()<\/span>\n{<\/span>\n <\/span>TWBR<\/span> <\/span>=<\/span> <\/span>2<\/span>;<\/span>\n}<\/span>\n\n\/\/ NB: clearing TWINT starts next transmission<\/span>\n\/\/ TWI == I2C<\/span>\n\/\/ TWCR = TWI Control Register<\/span>\n\/\/ TWDR = TWI Data Register<\/span>\n\n\/\/ start master transmission<\/span>\nstatic<\/span> <\/span>void<\/span> <\/span>i2c_start<\/span>()<\/span>\n{<\/span>\n <\/span>\/\/ clear TWINT flag, send START, enable TWI unit<\/span>\n <\/span>TWCR<\/span> <\/span>=<\/span> <\/span>_BV<\/span>(<\/span>TWINT<\/span>)<\/span> <\/span>|<\/span> <\/span>_BV<\/span>(<\/span>TWSTA<\/span>)<\/span> <\/span>|<\/span> <\/span>_BV<\/span>(<\/span>TWEN<\/span>);<\/span>\n <\/span>loop_until_bit_is_set<\/span>(<\/span>TWCR<\/span>,<\/span> <\/span>TWINT<\/span>);<\/span>\n <\/span>
![ANSI\nUS QWERTY (Windows, split + rotated)<\/a>,](\"https:\/\/commons.wikimedia.org\/wiki\/File:ANSI_US_QWERTY_(Windows,_split_+_rotated).svg\"){kind=link}