Audio Quality

Some studies have pointed out that the human brain puts together both audio and images as a single message and therefore audio has a tremendous impact on viewer experience. Some research has even pointed out that viewers are less likely to completely view a video clip if the audio quality is poor.

Below is a list of audio encoding artifacts to check for as well as some tips.

• Lip-sync. Most people find "out-of-sync" audio as unacceptable.
• Audio drop outs and pre- echo are perceived as “very annoying” artifacts by most people. They tend to be more prevalent in material that is percussive like a gunshot or a drum hit. Increase the bit rate as much as possible to compensate.
• Narrow audio program bandwidth. If high audio frequencies have been removed, the audio will sound “nasal” or “muddy”. If Low audio frequencies have been removed, the audio will sound “thin” and “harsh”. Make sure the resulting audio covers as much frequency spectrum as the original. Keep the audio sampling rate the same as the source or above 44.1 KHz for best results.
• “Garbled” audio due to over compression tends to have sort of an underwater sound. These artifacts will be more noticeable in material that has random characteristics like rain, applause or city traffic. Give enough bits to the audio stream. Try to keep audio bitrates above 96 kbs for best results.
• Summing some stereo material to mono will cause phasing artifacts and audio dropouts. Experiment by taking only the left or only the right channel if you hear this artifact. You might get better results.
• Audio re-sampling or clock errors often have a metallic / ringing sound and can produce loud ticks. If you are encoding video from tape or other hardware playback device, make sure the audio is properly clocked and sync-locked. When using AES/EBU or SPDIF audio, clock your input device to the source’s digital signal as a rule of thumb.
• Make sure the audio is noise (hiss) free. Be careful of not going overboard if you have to pre-process the audio with noise suppression as you might induce more serious artifacts. Also, make sure that your audio has the required bit resolution. Today, 16 bit audio is common place. Avoid a lower value.