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Verizon POTS vs. SunRocket VOIP Sound Quality Tests

Test Overview
Here are audio tests to compare the quality between a Verizon "Plain Old Telephone Service" line and a VOiP line using the Telco System Access211 Analog Telephone Adapter with SunRocket. (http://sunrocket.com)

Methodology
I connected the Ensoniq soundcard line input through an isolation transformer to the speaker output of an old GTE phone. The circuitry is of high quality unlike many phones made today. The sound level simulates the actual level heard when using the phone. I didn't amplify anything. I recorded with Cool Edit, at 16 bit, 44 Khz. I encoded these to MP3 VBR at 70% quality, (which to me sounds the same as the original files.)

I called two 800 numbers that have a "voice prompt" system which uses a real recorded human voice. I repeated the test 2 times with 2 different numbers for each provider.

My Observations
The VOiP is much louder than the POTS, and is easier to hear. It is also "sharper/harsher" sounding. I frequency analysis shows some more high-frequencies present in the VoIP. The POTS sound is weak, but possibly "smoother" than the VOiP. During my own testing I did amplify the POTS sound to match the VOiP but it didn't make it clearer sounding--just more hissy.

The first 800 number was sufficienly loud, but the second was pretty weak, maybe 8 dB to 12 dB lower! This is a common problem with POTS lines and if a second phone is picked up the sound level sometimes drops to hardly intelligeable levels. With POTS, I often had to raise the volume all the way with my cordless AT&T phone, but with The Access211 output, I usually have it half-way up and sometimes I have to turn it down all the way! There is plenty of volume there to pick up an extension and still be able to hear fine.

I tried to do some frequency reponse analysis in Cool Edit but I am not quite sure how to interpret the results. Maybe one of you can help with better analysis.

Contact Information/Your commments
So here are the samples so you can listen to them for yourself... If you would like the original files, which are about 8 megs for each sample, let me know and I'll get them to you.

I can be contacted here: tekwiz@tektimes.com
or if you prefer with the form below.

Name:

Comments:

Click or Right-Click on the graphs to download the MP3 Files.

SUNROCKET VoIP

TEST 1

TEST 2

VERIZON POTS

TEST 1

TEST 2

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