View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0000960 | OBS-Studio | libobs | public | 2017-07-24 17:30 | 2019-03-04 11:53 |
| Reporter | Ochi | Assigned To | pkv | ||
| Priority | normal | Severity | minor | Reproducibility | always |
| Status | resolved | Resolution | fixed | ||
| Platform | OBS Studio | OS | All Systems | ||
| Product Version | 19.0.3 | ||||
| Target Version | 23.1.0 | Fixed in Version | 23.1.0 | ||
| Summary | 0000960: Audio from mono input quieter than in other recording programs | ||||
| Description | I could reproduce the following issue under Linux and Windows. I have switched from recording my mic using [insert some audio recording software like audacity or REAPER here] to recording it with OBS directly in order to synchronize it better with other audio and video inputs. I'm using a USB sound card with mono input. I need to boost the sound captured using OBS by about 3 db to get about the same volume as in other audio recording software. Switching to mono mode in OBS is not a solution for me (if it helps at all, haven't tested it) by the way since I also need to record other stereo audio tracks. Is it possible that the mono input is averaged with a silent track as if it was a stereo input with sound on only one channel or something the like? | ||||
| Tags | Has PR | ||||
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All channels averaged only if "Downmix to Mono" selected (main menu Edit>Advanced Audio Properties). |
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Thanks for the reply. Downmixing is not in use, but it doesn't seem to make a difference regarding the issue either. I noticed something else, at least under Linux, though: If I add a "Audio Input Capture (PulseAudio)" source in OBS, selecting the USB Audio Interface directly and then recording, I'm having the issue with the volume. If I select some other (stereo?) sound source in OBS and then switch the input independently from OBS (in pavucontrol in this case) to the USB Audio Device, the volume seems similar to the sound recorded in e.g. audacity. If you have a sound card with a mono mic input, you can try to reproduce it fairly easily by recording in OBS and audacity simultaneously and comparing the results. Maybe it is an issue with my particular USB sound card, I don't know. My guess, however, is that OBS detects the difference in the number of channels between input and output and does something. Can you maybe give me a hint where the averaging takes place in the code, if it does? |
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Okay, I have taken a look at the code. It seems to be a fundamental thing how ffmpeg works. The downmixing option is not involved, but the resampling that happens in obs-source.c (also in audio-io.c, but this is not relevant for the recording, I think, but maybe for other things). In both cases it uses the resampling implemented in audio-resampler-ffmpeg.c. Bottom line is that swr_convert, which is used in audio_resampler_resample(), seems to be the culprit. Given a 1-channel input and 2-channel output, it generates two quieter stereo streams. You can easily reproduce this using ffmpeg itself. Take a mono wav and do: ffmpeg -i mono.wav -ac 2 stereo.wav and compare them. I'm using ffmpeg 3.3.2 here. Now the question is, is this what we would expect swr_convert to do? Is this what we expect OBS to do? EDIT: To be clear, I think that the way ffmpeg works makes sense depending on what you expect. If a mono signal would actually be output by only one speaker, then distributing the signal over all channels to get the same total power output after the conversion makes sense. However, it might be a counterintuitive result in case of OBS (at least I think so). I'm used to the fact that a mono signal is usually output on all channels/speakers by common audio recording and editing tools. Of course, the user could increase the recording volume in OBS in this particular case of mono input and stereo output, but I'm not sure whether this could potentially decrease the audio quality by first narrowing and then widening the dynamic range again. Also, I'm not sure whether this should be something the user needs to be taught to do in the particular case of a mono input and a stereo output. |
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Don't know about mono input (I think it happens rarely), but stereo inputs with one muted channel is common behavior for OBS - because of mono mics connected to stereo line-in of the PC (usually for mic that require +48V and PC can do only +2.5...5V https://obsproject.com/forum/threads/downmix-to-mono-50.49865/#post-223380). Anyway, I think implementation of the option to increase volume of the audio source (by doubling channels) should be switchable option, to be able to make it ON/OFF for selected inputs only. |
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For my use case, it would even be beneficial to be able to choose whether to record in mono or stereo separately for each audio track. I'm recording stereo game sound on one track and the mono mic on a second track. Therefore it would even be more efficient to just have the mic track be a mono track if that's possible (I'm using Matroska as the container format). In fact, this is probably what the "Downmix to Mono" option could already be doing. If I'm not mistaken, what it actually does is "average all channels of the input and put the result on a stereo track". So maybe it would make sense to create the audio track as a 1-channel track, in case the Downmix option is selected for a particular audio track? |
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"Downmix to Mono" just bad wording of the option. Something like "Downmix to Planar Sound" is better, I think. It is required and should exist. Edit: cross-link the post here https://obsproject.com/forum/threads/please-allow-for-mono-recording-of-microphones-ill-explain-why.84834/page-2#post-372717 (It is about FFmpeg processing and default stereo panning option, -3dB) |
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PR here: https://github.com/obsproject/obs-studio/pull/1686 |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2017-07-24 17:30 | Ochi | New Issue | |
| 2017-07-25 08:58 | Suslik V | Note Added: 0002134 | |
| 2017-07-25 15:41 | Ochi | Note Added: 0002135 | |
| 2017-07-25 15:42 | Ochi | Note Edited: 0002135 | View Revisions |
| 2017-07-25 16:16 | Ochi | Note Added: 0002136 | |
| 2017-07-25 16:17 | Ochi | Note Edited: 0002136 | View Revisions |
| 2017-07-25 17:03 | Ochi | Note Edited: 0002136 | View Revisions |
| 2017-07-26 16:39 | Suslik V | Note Added: 0002141 | |
| 2017-07-26 20:57 | Ochi | Note Added: 0002142 | |
| 2017-07-26 21:03 | Ochi | Note Edited: 0002142 | View Revisions |
| 2017-07-26 21:03 | Ochi | Note Edited: 0002142 | View Revisions |
| 2017-07-27 05:01 | Suslik V | Note Added: 0002143 | |
| 2018-09-09 15:54 | Suslik V | Note Edited: 0002143 | View Revisions |
| 2019-02-24 02:00 | Fenrir | Assigned To | => pkv |
| 2019-02-24 02:00 | Fenrir | Status | new => assigned |
| 2019-02-24 13:03 | pkv | Note Added: 0004069 | |
| 2019-02-24 13:03 | pkv | Tag Attached: Has PR | |
| 2019-03-04 11:53 | pkv | Status | assigned => resolved |
| 2019-03-04 11:53 | pkv | Resolution | open => fixed |
| 2019-03-04 11:53 | pkv | Fixed in Version | => 23.1.0 |
| 2019-03-04 11:53 | pkv | Target Version | => 23.1.0 |
