Opus Recommended Settings

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

Mono/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)

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	Stereo mode	Bandwidth	typ SILK/CELT use	Music quality notes	Use cases/notes/competitive codecs
6 kbps	mono	4 kHz	SILK	Poor, muffled sound but intelligible lyrics.	-
8 kbps	mono	4 kHz	SILK	Poor, muffled but OK for bitrate	-
14 to 16 kbps	mono	6 kHz	SILK	Fairly Poor but OK for bitrate	Perhaps acceptable for incidental music
22 to 24 kbps	mono	8 kHz	SILK	Fair but OK for bitrate	OK for incidental music
32 kbps	mono	12 kHz	hybrid	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	stereo	12 kHz	hybrid/CELT	Moderately good stereo, reasonably bright treble (c.f. stereo cassette)	Stereo podcasts, audiobooks, very low bitrate music
48 kbps	stereo	20 kHz	CELT	Full bandwidth stereo music, some artifacts, rarely nasty	Stereo podcasts, audiobooks, low bitrate music
64 kbps	stereo	20 kHz	CELT	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	stereo	20 kHz	CELT	Full bandwidth stereo music, good quality approaching transparency	Music storage & high quality streaming. Beat LC-AAC, Vorbis, MP3 in listening test
112 kbps	stereo	20 kHz	CELT	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	stereo	20 kHz	CELT	Very close to transparency (needs more testing). Most modern codecs competitive (AAC-LC, Vorbis, MP3)	Music storage & streaming. Future download music sales.
256 kbps	stereo	20 kHz	CELT	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	stereo	20 kHz	CELT	Maximum possible stereo bitrate target (actual rate often less than 510 for default frame size). Most old and new lossy codecs competitive, plus near-lossless lossyWAV and WavPack lossy	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 lossless, lossyWAV, WavPack lossy or lossy transform/subband codecs like Vorbis, Musepack at very high settings.