Audio

Audio Sample Rates: Terminology vs Application

I’ve recently started to develop a grumpy streak with respect to the use of certain terminology with respect to telephony. Maybe telephony isn’t exactly the right word, let’s say that my unease arises from some odd terms surrounding audio quality in the context of communication. I think that some of the language needs to be more application sensitive.

A few years ago the world was a simpler place. The “Plain Old Telephone System” (aka POTS) was definitely a narrowband medium. Where “narrowband” implied digital sampling at 8 KHz and a useful audio channel of 300 Hz – 3,400 Hz.

Some people using more advanced systems enjoyed “wideband” audio. Wideband in that case was defined as a 16 KHz sampling yielding a useful audio channel of 50 Hz – 7 KHz. The TIA-920 standard, which I have referenced previously, spells this out. A variety of audio codecs can deliver this capability including; AMR-WB, EVRC-WB, G.722, G.722.1, CELT & Opus.

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An Interesting History Of Headphones

k240studioSome time ago I stumbled upon a nice article that proposed to be something of a history of headphones. It’s a fairly good effort on the part of the author. However, I would like to add my two-cents in reference to a couple of missing items that I think are significant.

When I was in school in the mid-1980’s I was studying music recording and broadcasting. I spent a lot of time in and around various recording studios around Toronto. The single most common headset that I saw at that time was the AKG K240 Studio monitors. These were the reference grade dynamic headphones used in many facilities at that time.

The K240s are genuinely, big-ole, cans. A circumaural headphone with a semi-open design they sound great, even today. They can be cleanly driven to excessive volumes if required. Fairly efficient, they can even be powered by a cell phone or iPod.

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Extending Our Whole House Audio To The Back Yard

audio-trioLike many people we have a wooden deck at the back of the house into the back yard. It has long been my intent to extend our ability to play music to the back yard, but it has only recently com to pass. It’s essentially the next step in my long standing plans to deploy Whole House Audio, a project that recalls some of the earliest posts to this site.

As I described so long ago, we love our Logitech Squeezeboxes. They still form the basis of how we play music around here, even though Logitech has abandoned the product line. In fact, when my one Squeezebox Touch died I was inspired to purchase another Squeezebox 3 on E-bay, just to have a spare.

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Confirming The Quality Of One’s Tools

Zoom-H2-Nexus7-AudioTool.jpgWhen experimenting with a new audio path I like to take measurements. Long ago, in an age of techno-pre-history known as the late 1980’s,  I craved what were then an emerging class of computerized test instruments, like the Audio Precision System One. Happily, today such costs are unwarranted given the current class of programmable smart devices. I’ve been very happy with Audio Tool For Android running on my Nexus 7 tablet.

If I am to trust the measurements that Audio Tool allows me to make I need to start by confirming the validity of it’s measure using a known reference signal. I was also making use of the Zoom H2 Handy Portable Stereo Recorder, so I decided to record the output of the sweep generator in Audio Tool to the H2. Then I tool the resulting WAV file into Adobe Audition to see what resulted.

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Experimenting with Opus I: PhonerLite

Opus-LogoInspired by my earlier interaction with Mike Phillips I thought it would be interesting to get some hands on experience with Opus. It would be worthwhile staging a little test to better understand the audio path presented in one or more Opus implementations.

A quick Google search revealed that PhonerLite, the freeware Windows soft phone from Germany, includes Opus from the v1.92 release onward. According to the release notes support for Opus replaced support for CELT. The current release is v2.08 from April 16, 2013.

I had first encountered PhonerLite some time ago, when I was seeking a G.722 capable soft phone. It’s very functional but a bit quirky.

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Considering Opus Implementations

Opus-over-skypeOpus promises to be a great tool for online audio. In technology, as in music, not all opus are implemented equally. Allow me to explain.

Earlier this week I happened into a Twitter exchange with Mike Phillips. Mike is a podcaster. VUC founder Randy Resnick has introduced us once before. Mike is seeking a replacement for the role that Skype plays in his online toolbox.

It came to light that Mike has tried to leverage various soft phones, even giving some focus to finding one that implements the Opus codec. Opus is after all, open source, the current state-of-the-art in audio codecs, and a new IETF standard. However, in Mike’s attempts to tap its potential he has to date come up short relative to Skype.

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