Am trying to wean our house off of analog land-line for telco, and have bought an OOMA. My wife, who has very good hearing (ie, good high end sensitivity) complains that the OOMA sound is harsh and tinny. We have tried it to and from many places and I presume that the combination of VoIP phones in nearly every location is passing somewhat better than the normal 3K of Ma Bell. The low end seems fine to me. I have long ago lost my Hadnbook of Electronic circuits, so need to ask for help in designing a simple low-pass filter for the telco line that OOMA outputs (presume similar characteristics to Ma Bell) to roll-off the highs starting at around 6 dB or so around 2800 Hz. (I can always tune it if needed by small tweaks).

If memory serves, I would likely be best off with a two stage LC filter(?) Any advice to where I can find the basic design and formulas for cut-offs would be appreciated.

Thanks

 

Am trying to wean our house off of analog land-line for telco, and have bought an OOMA. My wife, who has very good hearing (ie, good high end sensitivity) complains that the OOMA sound is harsh and tinny.

I know what you mean. I had an OOMA for a short time (had to return it because of a line incompatibility with my home alarm system), and also noticed that the sound somewhat over-emphasized the highs (and my old hearing isn't that good) to the point of it being annoying.

I would likely be best off with a two stage LC filter(?)

A standard POTS line is a current-loop circuit with about a 300Ω source resistance and a 180Ω telephone resistance.
Just a capacitor connected across the telephone line might work.
Start with about 0.47μF and see what effect that has.

 

I know what you mean. I had an OOMA for a short time (had to return it because of a line incompatibility with my home alarm system), and also noticed that the sound somewhat over-emphasized the highs (and my old hearing isn't that good) to the point of it being annoying.

A standard POTS line is a current-loop circuit with about a 300Ω source resistance and a 180Ω telephone resistance.
Just a capacitor connected across the telephone line might work.
Start with about 0.47μF and see what effect that has.

Thanks! had tried capacitors earlier, although not sure I went up to 0.47. Will give it a try and report back