Please provide more information about what hardware and/or VoIP service you are using with IVM.
When using analogue telephony interfaces, the quality of the call is highly dependent on the voice modem or telephony board you have purchased. The quality can range considerably depending on the brand and overall build quality. For voice modems, some have been known to produce unacceptable quality like you descibe while others have been known to produce the high quality call you might expect from picking up your traditional wireline telephone. Telephony boards typically provide much higher quality calls to IVM, and they are trusted for use in professional environments. If you want to still interface your analogue line with IVM, I suggest you look into purchasing a higher quality voice modem (approximately $35 - $50) or a professional telephony board (often in excess of $200 however).
If you are using VoIP lines with IVM, quality may be reduced due to several factors including:
- The speed/bandwidth of the connection
- Whether the router on your network provides Quality of Service (QoS) features to prioritize VoIP communications over other "less important" network traffic
- The distance between you and the VoIP provider's server
- The codec that is being used / the quality level that has been set in IVM (contrary to what you may believe, the quality setting should be set to 'low' to improve call quality in environments where there is a low bandwidth/slower internet connection available. The high quality setting is only effective if the internet connection is able to handle streaming of excessively large data packets without disruption
- Whether the firewall has been set-up to forward the required VoIP ports and allow for a free flow of VoIP packets through the router (not forwarding the ports will cause delays, break-ups in sound, and possible total loss of communication
and more factors