ATIS T1.TR.80-2003

This Technical Report (TR) documents the descriptors listeners use in characterizing how speech sounds when it has been modified by passing through a Internet Protocol (IP) network and data packets have been lost or their timing has been disturbed. This TR demonstrates how the effects of the loss and jitter impairments sound through the use of embedded audio files. A standard set of speech recordings were modified by passing through G.711 and G.729 codecs produced by two different manufacturers, and were further modified by being operated on by the NIST Net network emulator. The emulator allows packet loss and packet delay variation to be manipulated parametrically. The modified speech recordings were subjectively evaluated by consumers (i.e., non-expert judges). The consumers described the sound of the speech samples from the various combinations of codec and network performance an a set of verbal descriptors was derived. A second set of consumers rated the speech recordings with respect to the verbal descriptors. A suite of 10 ratings of each speech sample is presented along with its recording.