5 ms·

Show HN: Intentionally subtle headphone crossfeed filter

51 points by LnxPrgr3 12y ago

LnxPrgr3 12y ago
Disclaimer: was inspired to post by this: https://news.ycombinator.com/item?id=8816344 https://news.ycombinator.com/item?id=8816344. You should check out his work too. He attempts to simulate surround sound—my program limits itself to stereo audio. This filter is designed to be unobtrusive—ideally, it's easier to hear the effect of turning it off than turning it on. A huge goal was preserving my headphones' frequency response—I chose them because they sounded great to me in that regard, and I wasn't about to break that to fix stereo imaging. If you're lacking a Mac or the desire to deal with the libsndfile version, here's a demo: https://www.dropbox.com/s/t5dvah8zke3uky8/HellOfAGuy_demo.mp3 https://www.dropbox.com/s/t5dvah8zke3uky8/HellOfAGuy_demo.mp.... The source audio came from http://www.audiogroup.web.fh-koeln.de/anechoic.html http://www.audiogroup.web.fh-koeln.de/anechoic.html.
jbk 12y ago
This seems cool. How portable is the actual filter code? It seems to use Accelerate framework.
- LnxPrgr3 12y ago
  The filter lives in crossfeed.c, with an API described in crossfeed.h. It's pure math and makes no system calls itself—should be plenty portable. The filter designer does use Accelerate, but it's only needed to generate arrays for crossfeed.c. Porting to another FFT lib should be easy enough, though I should mention I need to update the designer in this code: the current version was made through this header library: https://gist.github.com/LnxPrgr3/8262666 https://gist.github.com/LnxPrgr3/8262666
Kiro 12y ago
I'm not on a Mac so I can't test this right now but I don't know if I think this sounds like a good idea. The stereo image is a big part of the mix down, especially in bass heavy electronic music where a lot of big sounds need to compete for space in the frequency spectrum. Won't this possibly destroy the mix in those cases?
- LnxPrgr3 12y ago
  It shouldn't, unless the mix down was done for headphones. If it wasn't mixed for headphones, the problem is headphones exaggerate stereo separation. See: http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/localization/localization.html http://www.cns.nyu.edu/~david/courses/perception/lecturenote... The goal is to simulate playback on speakers. If it breaks music mastered for speakers, I'd consider that a bug.
deleted 12y ago
[deleted]
- deleted 12y ago
  [deleted]
ankushio 12y ago
I tried this with over half a dozen songs, including the one listed on the README (Ingrid Michaelson- Be Ok), but I am unable see the difference when I turn the crossfeed filter ON/OFF. I can't tell the difference whether the filter is on or off. I am using iPhone's default headphones while listening to these songs. Am I doing something wrong? Is the difference very subtle?
- LnxPrgr3 12y ago
  I would've thought headphone quality mattered, but my boss heard the effect through iPhone earbuds. The effect is fairly subtle. To make it as clear as possible, try leaving it on for a couple minutes, then switch it off and listen for a bit. Or, play this example, which is the clearest demo I've found: https://www.dropbox.com/s/t5dvah8zke3uky8/HellOfAGuy_demo.mp3 https://www.dropbox.com/s/t5dvah8zke3uky8/HellOfAGuy_demo.mp.... The song's played twice—with and without the filter.
thisjepisje 12y ago
What does it actually do? When a part is recorded to a single stereo track only, it can sound pretty unnatural (sometimes even annoying - makes me feel like I'm half deaf...) on headphones. The only thing I'd really want to do to avoid this is mix the mono signal with the stereo, so that 100% right becomes e.g. 75% right and 25% left. (Fully mono would be 50/50 on all sounds, obviously).
- LnxPrgr3 12y ago
  Turns out, we have two left-right localization cues—intensity difference, and timing difference. Sounds on the left hit the right ear a bit late and filtered. This filter aims to reproduce that, effectively mimicking well-placed stereo speakers on headphones.
  - thisjepisje 12y ago
    Thanks for the clarification. I've played a bit with the Haas effect myself, it's a nice way to separate sounds when you do mix for headphones. Besides the delay, what filter does your program apply when carrying stuff from the left to the right?
    - LnxPrgr3 12y ago
      This is the goal transfer function (x is frequency in Hz): return pow(10, (x <= 250 ? 1 : 1 + 1.5*log2(x/250) + (x > 5000 ? 5*log2(x/5000) : 0)) / -20); This is the header library that generated the filter to match this as closely as possible: https://gist.github.com/LnxPrgr3/8262666 https://gist.github.com/LnxPrgr3/8262666 Then, it's time-reversed and the sign flipped, and an impulse is added at sample 0. This filter translates to mid/side stereo, applies this kernel to the side channel, then converts back to L/R for playback.
      - fl0wenol 12y ago
        Is that based on a comb filter with truncated notches at 250 and 5000 Hz (a 2ms phase separation where applied)?
ubercow13 12y ago
I've been using this one for foobar2000 since I can remember - http://www.naivesoftware.com/software.html http://www.naivesoftware.com/software.html. It's also subtle but effective. The qualitative difference is that it sounds, for example, like the band is playing in front of you, not that you have two speakers stuck to the sides of your head.
dsr_ 12y ago
A long time ago, recordings were made by putting a microphone or three in a place near where the audience was sitting at a performance. If you get it right -- don't flip the phase of the signals, use appropriate microphones, and get good levels all the way through, record to a really good medium -- you can get amazing results. If you are certain that the music will be played back through headphones, you can embed two mikes in a mock-up of a human head -- better yet, inside the ears, and require playback through in-ear monitors -- and get an amazing sense of realism. That's not the way most music is produced these days, though. That's like a single-author software project with everything written from scratch: there are some, but not many. Music is rarely made in real-time at a live performance. It's usually made in an editing suite after dozens, hundreds or even thousands of individual recordings, samples and synthesized effects are made, gathered or licensed. These elements are brought together, altered, fused, and made into a final bitstream that represents the producer's best effort at realizing their musical intent. You can get amazing things out of that process, too. Works that could not reasonably be made any other way. However, in that workflow, the original real world spaces in which the source materials were made -- if any -- are mixed and lost. To produce stereo in a two-channel final recording, many tracks are simply assigned to one channel or both channels at specified volumes. This loses or confuses phase and delay information that humans use for spatial location. The crossfeed filters are another post-processing step, this time in the hands of the audience playing it back, that can simulate some of that spatial location information. It can do this to a greater or lesser degree; the more information available at the beginning of the process (about spatial location), the more can be introduced. Eventually we might see artists routinely producing multiple final products, some of which have been rendered to virtual spaces for headphones or IEMs, others being set for surround configurations or stereo playback. Better software tools will help with that -- a scriptable 3D GUI that places your virtual instruments and virtual audience in a virtual ambience could be immensely useful.
- okiejonwilliams 12y ago
  In-ear binaural microphones can be used to reproduce in with headphones what a listener hears during a live performance.
  - 12y ago
freework 12y ago
Here is an example song that would benefit from a plug in like this: https://www.youtube.com/watch?v=KeIQvxSS2M8 https://www.youtube.com/watch?v=KeIQvxSS2M8. The guitar riff that hard pans from left to right can sound jarring when listening with headphones without a crossfeed filter. With the filter, the sound is more natural. I'm surprised apple hasn't added crossfeed functionality to any of their audio products. I remember discovering crossfeed back in the early 2000s. My audio player was foobar2000 which had a plugin to do crossfeed. When I switched to Mac in the late 2000s, I had to go back to listening to music without crossfeed. It still perplexes me that with the explosion of high end headphone popularity that this hasn't become a standard feature for audio players.
okiejonwilliams 12y ago
The most accurate way to make a stereo recording sound like it's coming from two speakers when listening with headphones is to use the head-related transfer function (HRTF), which phases and filters audio sources in a virtual 3-D space in the same way that their positions, the human head, and ears do. When waves pass through the head and ears from different directions, the loudness and frequency content is changed before it reaches the sensors in the inner ear.

51 points by LnxPrgr3 12y ago

Disclaimer: was inspired to post by this: https://news.ycombinator.com/item?id=8816344 https://news.ycombinator.com/item?id=8816344. You should check out his work too. He attempts to simulate surround sound—my program limits itself to stereo audio. This filter is designed to be unobtrusive—ideally, it's easier to hear the effect of turning it off than turning it on. A huge goal was preserving my headphones' frequency response—I chose them because they sounded great to me in that regard, and I wasn't about to break that to fix stereo imaging. If you're lacking a Mac or the desire to deal with the libsndfile version, here's a demo: https://www.dropbox.com/s/t5dvah8zke3uky8/HellOfAGuy_demo.mp3 https://www.dropbox.com/s/t5dvah8zke3uky8/HellOfAGuy_demo.mp.... The source audio came from http://www.audiogroup.web.fh-koeln.de/anechoic.html http://www.audiogroup.web.fh-koeln.de/anechoic.html.

jbk 12y ago

This seems cool. How portable is the actual filter code? It seems to use Accelerate framework.

LnxPrgr3 12y ago
The filter lives in crossfeed.c, with an API described in crossfeed.h. It's pure math and makes no system calls itself—should be plenty portable. The filter designer does use Accelerate, but it's only needed to generate arrays for crossfeed.c. Porting to another FFT lib should be easy enough, though I should mention I need to update the designer in this code: the current version was made through this header library: https://gist.github.com/LnxPrgr3/8262666 https://gist.github.com/LnxPrgr3/8262666

Kiro 12y ago

I'm not on a Mac so I can't test this right now but I don't know if I think this sounds like a good idea. The stereo image is a big part of the mix down, especially in bass heavy electronic music where a lot of big sounds need to compete for space in the frequency spectrum. Won't this possibly destroy the mix in those cases?

LnxPrgr3 12y ago
It shouldn't, unless the mix down was done for headphones. If it wasn't mixed for headphones, the problem is headphones exaggerate stereo separation. See: http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/localization/localization.html http://www.cns.nyu.edu/~david/courses/perception/lecturenote... The goal is to simulate playback on speakers. If it breaks music mastered for speakers, I'd consider that a bug.

deleted 12y ago

[deleted]

deleted 12y ago
[deleted]

ankushio 12y ago

I tried this with over half a dozen songs, including the one listed on the README (Ingrid Michaelson- Be Ok), but I am unable see the difference when I turn the crossfeed filter ON/OFF. I can't tell the difference whether the filter is on or off. I am using iPhone's default headphones while listening to these songs. Am I doing something wrong? Is the difference very subtle?

LnxPrgr3 12y ago
I would've thought headphone quality mattered, but my boss heard the effect through iPhone earbuds. The effect is fairly subtle. To make it as clear as possible, try leaving it on for a couple minutes, then switch it off and listen for a bit. Or, play this example, which is the clearest demo I've found: https://www.dropbox.com/s/t5dvah8zke3uky8/HellOfAGuy_demo.mp3 https://www.dropbox.com/s/t5dvah8zke3uky8/HellOfAGuy_demo.mp.... The song's played twice—with and without the filter.

thisjepisje 12y ago

What does it actually do? When a part is recorded to a single stereo track only, it can sound pretty unnatural (sometimes even annoying - makes me feel like I'm half deaf...) on headphones. The only thing I'd really want to do to avoid this is mix the mono signal with the stereo, so that 100% right becomes e.g. 75% right and 25% left. (Fully mono would be 50/50 on all sounds, obviously).

LnxPrgr3 12y ago
Turns out, we have two left-right localization cues—intensity difference, and timing difference. Sounds on the left hit the right ear a bit late and filtered. This filter aims to reproduce that, effectively mimicking well-placed stereo speakers on headphones.
- thisjepisje 12y ago
  Thanks for the clarification. I've played a bit with the Haas effect myself, it's a nice way to separate sounds when you do mix for headphones. Besides the delay, what filter does your program apply when carrying stuff from the left to the right?
  - LnxPrgr3 12y ago
    This is the goal transfer function (x is frequency in Hz): return pow(10, (x <= 250 ? 1 : 1 + 1.5*log2(x/250) + (x > 5000 ? 5*log2(x/5000) : 0)) / -20); This is the header library that generated the filter to match this as closely as possible: https://gist.github.com/LnxPrgr3/8262666 https://gist.github.com/LnxPrgr3/8262666 Then, it's time-reversed and the sign flipped, and an impulse is added at sample 0. This filter translates to mid/side stereo, applies this kernel to the side channel, then converts back to L/R for playback.
    - fl0wenol 12y ago
      Is that based on a comb filter with truncated notches at 250 and 5000 Hz (a 2ms phase separation where applied)?

ubercow13 12y ago

I've been using this one for foobar2000 since I can remember - http://www.naivesoftware.com/software.html http://www.naivesoftware.com/software.html. It's also subtle but effective. The qualitative difference is that it sounds, for example, like the band is playing in front of you, not that you have two speakers stuck to the sides of your head.

dsr_ 12y ago

A long time ago, recordings were made by putting a microphone or three in a place near where the audience was sitting at a performance. If you get it right -- don't flip the phase of the signals, use appropriate microphones, and get good levels all the way through, record to a really good medium -- you can get amazing results. If you are certain that the music will be played back through headphones, you can embed two mikes in a mock-up of a human head -- better yet, inside the ears, and require playback through in-ear monitors -- and get an amazing sense of realism. That's not the way most music is produced these days, though. That's like a single-author software project with everything written from scratch: there are some, but not many. Music is rarely made in real-time at a live performance. It's usually made in an editing suite after dozens, hundreds or even thousands of individual recordings, samples and synthesized effects are made, gathered or licensed. These elements are brought together, altered, fused, and made into a final bitstream that represents the producer's best effort at realizing their musical intent. You can get amazing things out of that process, too. Works that could not reasonably be made any other way. However, in that workflow, the original real world spaces in which the source materials were made -- if any -- are mixed and lost. To produce stereo in a two-channel final recording, many tracks are simply assigned to one channel or both channels at specified volumes. This loses or confuses phase and delay information that humans use for spatial location. The crossfeed filters are another post-processing step, this time in the hands of the audience playing it back, that can simulate some of that spatial location information. It can do this to a greater or lesser degree; the more information available at the beginning of the process (about spatial location), the more can be introduced. Eventually we might see artists routinely producing multiple final products, some of which have been rendered to virtual spaces for headphones or IEMs, others being set for surround configurations or stereo playback. Better software tools will help with that -- a scriptable 3D GUI that places your virtual instruments and virtual audience in a virtual ambience could be immensely useful.

okiejonwilliams 12y ago
In-ear binaural microphones can be used to reproduce in with headphones what a listener hears during a live performance.
- 12y ago

freework 12y ago

Here is an example song that would benefit from a plug in like this: https://www.youtube.com/watch?v=KeIQvxSS2M8 https://www.youtube.com/watch?v=KeIQvxSS2M8. The guitar riff that hard pans from left to right can sound jarring when listening with headphones without a crossfeed filter. With the filter, the sound is more natural. I'm surprised apple hasn't added crossfeed functionality to any of their audio products. I remember discovering crossfeed back in the early 2000s. My audio player was foobar2000 which had a plugin to do crossfeed. When I switched to Mac in the late 2000s, I had to go back to listening to music without crossfeed. It still perplexes me that with the explosion of high end headphone popularity that this hasn't become a standard feature for audio players.

okiejonwilliams 12y ago

The most accurate way to make a stereo recording sound like it's coming from two speakers when listening with headphones is to use the head-related transfer function (HRTF), which phases and filters audio sources in a virtual 3-D space in the same way that their positions, the human head, and ears do. When waves pass through the head and ears from different directions, the loudness and frequency content is changed before it reaches the sensors in the inner ear.