Opus Recommended Settings

Depending on what kinds of sounds you want to encode with Opus, you'll want different settings.

Mono or Stereo

Opus tends to start downmixing stereo inputs to mono from roughly 30 Kb/s and lower. You can check the details in the opus_encoder.c source file.

You can force downmixing by using the following command-line parameters:

--downmix-mono - downmixes input channels to mono

--downmix-stereo - downmixes input channels to stereo (if there are more than 2)

SILK, CELT and Hybrid Modes

Opus can operate under any of the following 3 modes:

• SILK: uses only the SILK codec (which is specialised at encoding speech)
• CELT: uses only the CELT codec (which is specialised at encoding music)
• Hybrid: splits the input into low frequencies which are encoded with SILK, and high frequencies which are encoded with CELT.

Bandwidth Transition Thresholds

The following table shows where Opus decides to switch between different bandwidths. It was copied from the opus_encoder.c source file.

(bitrates in Kb/s)	Mono		Stereo
	Voice	Music	Voice	Music
NB ↔ MB	11 ± 1	12 ± 1	11 ± 1	12 ± 2
MB ↔ WB	14 ± 1	15 ± 1	14 ± 2	18 ± 2
WB ↔ SWB	17 ± 1	18 ± 1	21 ± 2	21 ± 2
SWB ↔ FB	21 ± 1	22 ± 2	28 ± 2	30 ± 2

Usage Table

The following table has rough guidelines to help you get your required quality, file size or latency. The table is originally taken from the HydrogenAudio wiki, which has some great information on Opus and its usage.

Bitrate target	Music quality notes	Use cases/notes/competitive codecs
6 kbps	Poor, muffled sound but intelligible lyrics.	-
8 kbps	Poor, muffled but OK for bitrate	-
14 to 16 kbps	Fairly Poor but OK for bitrate	Perhaps acceptable for incidental music
22 to 24 kbps	Fair but OK for bitrate	OK for incidental music
32 kbps	Moderately good mono, reasonably bright treble (c.f. mono cassette)	Good for podcasts, audiobooks, CELT-only poss for music. Competitor HE-AAC@32kbps is stereo full-band but with annoying artifacts.
36 to 40 kbps	Moderately good stereo, reasonably bright treble (c.f. stereo cassette)	Stereo podcasts, audiobooks, very low bitrate music
48 kbps	Full bandwidth stereo music, some artifacts, rarely nasty	Stereo podcasts, audiobooks, low bitrate music
64 kbps	Full bandwidth stereo music, nice sound, detectable differences to original (mostly 'not annoying')	Music storage & streaming. Beat HE-AAC, Vorbis, MP3 in listening test
96 kbps	Full bandwidth stereo music, good quality approaching transparency	Music storage & high quality streaming. Beat LC-AAC, Vorbis, MP3 in listening test
112 kbps	Fairly close to transparency (needs more testing)	Music storage & high quality streaming. Very low-latency stereo networked music performance/jam sessions at OK quality (see below table)
128 kbps	Very close to transparency (needs more testing). Most modern codecs competitive (AAC-LC, Vorbis, MP3)	Music storage & streaming. Future download music sales.
256 kbps	Transparent with very low chance of artifacts (a few killer samples still detectable). Most old & new lossy codecs competitive.	Music storage & streaming, dedicated limited-bandwidth audio links (e.g. wireless, A2DP-bluetooth type links).
510 kbps	Maximum possible stereo bitrate target (actual rate often less than 510 for default frame size). At these bitrates, you probably want to be using FLAC...	Music storage, dedicated limited-bitrate audio links (e.g. wireless, minimum latency high quality audio. LossyWAV and WavPack lossy are very competitive for storage, and WavPack lossy --blocksize=256 may be competitive with minimum latency mode also.
>510 kbps	Above Opus bitrate range allowed for stereo sources.	Settle for 510kbps or use FLAC.