Getting Root On Linux Amplifier Adds New Inputs

We remember when getting Linux on your average desktop computer was a tricky enough endeavor that only those with the most luxurious of graybeards would even attempt it. A “Linux box” in those heady days was more than likely an outdated machine salvaged from the dumpster, side panel forever removed, cranking away in a basement or garage. Fast forward today, and Linux is literally everywhere: from smartphones and luxury cars, to TVs and refrigerators. Ironically it’s still not on most desktop computers, but that’s a discussion for another time.

So when [Michael Nothhard] sent in the fascinating account of how he hacked his Linux-powered Bluesound Powernode N150 amplifier to unlock more inputs, the least surprising element was that there was a “smart amplifier” out there running the free and open source operating system. What piqued our interest was that he was able to bust his way in with relative ease and enable some impressive new capabilities that the manufacturer would probably have rather been kept under wraps.

Configuring the CM6206’s audio settings.

[Michael] explains that the N150 has a USB port on the back side of it, and that officially, it only works with mass storage devices and a handful of approved peripherals such as a Bluetooth dongle. But as he was hoping to connect some more devices to the input-limited amplifier, he wondered if he could get a USB audio adapter recognized by the OS. After using a known exploit to get root access, he started poking around at the underlying Linux system to see what kind of trickery the developers had done.

Based on a fairly common C-Media CM6206 chipset, the StarTech 7.1 USB audio adapter was picked up by the kernel without an issue. But to actually get it working with the amplifier’s stock software, he then needed to add a new <capture> entry to the system’s sovi_info.xml configuration file and make some changes to its default ALSA settings. With the appropriate files modified, the new USB audio input device popped up under the official Bluesound smartphone application.

At the end of the write-up [Michael] notes that you’ll need to jump through a few additional hoops to make sure that an upstream firmware update doesn’t wipe all your hard work. Luckily it sounds like backing up the configuration and returning it to the newly flashed Powernode is easy enough. We’ve certainly seen more elaborate methods of gaining control of one’s sound system over the years.

Fixing Linux Audio One Chipset At A Time

Linux audio may be confusing for the uninitiated. As a system that has evolved and spawned at least two independent branches over time it tends to produce results that surprise or irritate the user. On the other hand it is open source software and thus can be fixed if you know what you do.

Over at reddit [rener2] was annoyed by the fact that listening to music on his laptop was a significantly worse experience under Linux than under Windows. Running Windows the output of  the headphone jack covered the whole spectrum while his Linux set up cut off the low end resulting in a tinny sound. The culprit in this is the sound card: it has two different output paths for the internal speakers and the headphone jack. The signal for the internal speakers is routed through a high pass filter to spare them the embarrassment of failure to reproduce low frequencies.

When headphones are plugged in, the sound card driver is supposed to make the sound card bypass the filter and deliver the full spectrum. The authors of the Windows driver knew this and had it taken care of. In his video [rener2] runs us through the process of patching the ALSA driver while referencing the documentation of a sound card that he deems ‘similar enough’ to his Realtek ALC288.

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RaspiDrums Uses Expensive Sensors

Piezoelectric sensors are great for monitoring mechanical impacts with a microcontroller. Whether you’re monitoring knocks on a door or watching a heartbeat, they are a cheap way to get the job done. They do have their downsides, though, so when [Jeremy] wanted to build an electronic drum set, he decided to use more expensive accelerometers to measure the percussive impacts instead.

Even though piezo sensors are cheap, they require a lot of work to get them working properly. The ADXL377 3-axis accelerometer that [Jeremy] found requires much less work, plus provides more reliable data due to a 1kHz low-pass filter at the output. In his setup, a Raspberry Pi handles all of the heavy lifting. An ADC on each drum sends data about each impact of the drum, and the Raspberry Pi outputs sound via the native Alsa driver and a USB sound card.

This project goes a long way to show how much simpler a project like this is once you find the right hardware for the job. [Jeremy]’s new electronic drums are very well documented as well if you are curious about using accelerometers on your newest project rather than piezo sensors. And, if you’re into drums be sure to see how you can have drums anywhere, or how you can build your own logic drums.

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Ti Chronos Watch Controls Raspberry Pi

[Mike Field] was working on interfacing his TI Chronos eZ430 watch with the Raspberry Pi. As things were going pretty well, he took a side-trip from his intended hack and implemented watch-based control for an RPi audio player.

It really comes as no surprise that this is possible, and even easy. After all, the RPi board has native USB capability for hosting the watch‘s RF dongle, and it’s running Linux which we know already works well with the Chronos platform. But we still love the thought of having automation controls strapped to our wrist!

mpg321 is the audio playback program used for this hack. It plays MP3 files using ALSA for sound, which does have a few hiccups on the RPi. [Mike] found workarounds and included them in the C program he uses to gather everything into one nice code package. Control depends on keypresses sent from the watch (meant for use with PowerPoint) which are translated by his code and pushed to the audio/mp3 programs.