Plantronics Audio 655 Stereo Headset Review (for linguists)

The Plantronics Audio 655 Stereo Headset is a relatively new (February 2010) product and certainly one that I never expected I would consider for the purposes of speech recording. The headset is designed primarily for VoIP applications, such as Skype, and, as such, does a splendid job. Granted, I have only tested it on Windows XP Professional, Windows 7 Professional, and Linux Ubuntu 9.10, but it does live up to its advertising hype in providing a truly plug-and-play USB headset that simply works. You plug it into an available USB port, and you're ready to use it almost instantaneously. The headset works very well with Skype, which is why I bought it in the first place. However, I was nicely surprised with the recording sound quality. Because its low price (around $40) and ease of use, I decided to consider this unit as a possible speech recording microphone for non-critical speech analysis projects.

Signal processing

The Plantronics Audio 665 headset uses proprietary signal processing (a.k.a "noise canceling") which makes the unit work very well for telecommunications, but which renders the recorded signals unreliable for detailed analysis. The manufacturer advertises the frequency response as ranging from 100 Hz to 8,000 Hz, but the low-end is certainly not perfectly flat down to 100 Hz. The unit probably employs some sort of bass roll-off filter, to cut down on the low-frequency rumble, typically present in people's offices (e.g., computer fans, air conditioners, etc.). This is evident in the FFT in Figure 2.

Low-frequency hum

I have tried the headset with three different computers, including a battery-powered laptop and was not able to get rid of the low-frequency hum (see Figure 2) which registered at around -36 dB FS. While this should not interfere with VoIP communications, it does pose a rather serious issue for detailed acoustic analysis of speech.

Good spectral detail

The headset is able to record surprisingly good spectral detail, as evidenced in Figure 1. I would not hesitate to recommend the unit to undergraduate students to be used for learning purposes, including simple formant analysis. Students would be able to get a lot of mileage out of this unit, particularly due to its failsafe ease of use.

Recommendations

By all means, you should fee comfortable recommending the headset to students for non-critical projects. The unit will most certainly trump built-in laptop microphones, iPods, and other non-specialist digital recorders. The close microphone placement, by itself, will guarantee good spectral detail and favorable signal-to-noise ratio.

Audio tests

Very decent spectral detail, particularly in formant tracks. The low-frequency hum (Figure 1) and low-frequency roll-off (Figure 2) are problematic for serious acoustic analysis. However, it most likely that the hum was just specific to my location and set up. I tested the headset on two computers, one running on battery power, but the hum be specific to my location and electrical wiring. It is perfectly possible that you will not experience the hum, so please, take that into account.

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Figure 1 Spectrogram of a Polish phrase "Czarna krowa." Note the low-frequency hum throughout the utterance.

Figure 2. FFT of the vowel /a/. Note amplitude attenuation in the low frequency region (< 250 Hz).