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)
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.
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
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.
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.
can be contacted here:
or if you prefer with the form below.
Click or Right-Click on the graphs to download
the MP3 Files.