Streaming Audio with Ices and Icecast
Once I had everything set up and running, I spent a fair amount of time fine-tuning the audio. The first thing I found was that the audio level was quite low. Normally, when I want to turn up the audio level, I use KMix. But, I hadn't installed a window manager on my encoding computer. My system uses ALSA as the sound system, and I found out that there is a great curses-based mixer for ALSA named Alsamixer. It allows you to use the arrow keys to change settings. Figure 4 shows the settings I chose for my card. My final preference was to have the Master and PCM both at 100%. I also chose to mute everything else, because I knew they would not be in use.
Now that the audio was loud enough, I still had another problem. The audio sounded choppy. After looking around for a while, I realized that the processor usage was at 100%. I tried to reduce the bitrate by changing the value of the nominal-bitrate setting. With the bitrate set sufficiently low, the audio sounded good. I guess you can't encode very high-quality audio with a 233MHz processor.
When the audio sounded good, my goal was to lower the bitrate as much as possible while keeping an acceptable level of audio quality. In my case, an “acceptable level” is quite low. The traffic on the W0ZWY repeater is only voice, because it is illegal to transmit music in the amateur radio bands.
Three aspects of the encoded audio will affect its quality and bitrate: number of channels, sample rate and bitrate. I started by setting the downmix to 1, because the scanner is only mono. Then, I incrementally decreased the sample rate until I found the lowest setting that rendered acceptable audio; 11127Hz ended up being the minimum. Instead of setting the bitrate with the nominal-bitrate setting, I used the quality setting. The quality setting directly affects the final bitrate. With a few tries, I chose a quality level of 2.
With my final settings, the bitrate stays around 30Kbps, and the processor hovers around 40% usage.
There are probably many other applications where this type of system would be useful. Keep in mind, however, if you are interested in using this type of system for streaming music, make sure you have permission from the artists and recording studios.
This combination of open-source projects really worked well together. Setting up everything was quite simple. I spent most of my time tweaking the quality and sample rate settings. The traffic on my streamer is quite low. I usually have only one or two connections per week. But, it was fun to learn, and it is my little way of participating in the amateur radio community.
Ices Settings and Bitrates
The quality, sample rate and channels settings all will affect the bitrate of the stream. Table 1 shows various combinations of these settings and their resulting bitrates.
Brian Matherly is a Software Engineer at Sencore Electronics in Sioux Falls, South Dakota. He is also an adjunct professor at Colorado Technical University.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide