Suppose you record all of a user’s voice conversations, and keep them on hard disk storage. How much storage will be required, and what will it cost?
First, some background:
- A pretty high-quality (CS-ACELP) digital encoding can be achieved at 8 kbits/sec. So this would require 3.6MB to store one hour of voice.
- A noticeably degraded (LPC10) digital encoding can be achieved at 2.4 kbits/sec. So this would require 1.08MB to store one hour of voice.
- The above encodings both produce a continuous bit rate without silence elimination. Storage-oriented (variable bit rate) encodings may achieve higher quality and yet require fewer bits.
- So figure a maximum of 5MB per hour.
Suppose a user spends one hour per day on the phone, for 200 days a year. That’s 1GB of storage per year. With large, moderate-performance (7.2 krpm), ATI-interfaced, hard drives employed in low-cost RAID5 arrays, storage costs (in one-off quantities) $1.60 to $2.10 per GB. The cost of online retention of voice, on a per-user basis, is trivial.