Here is a "for instance" for you... This is an Apple Lossless file of a digital recording of Bach. The first half is the recording as it appears on the CD. The second half is just the frequencies above 12kHz. ...
Silence... Yes, there isn't even anything above 12kHz in a lot of music, much less above 20kHz...
DISCLAIMER: I installed Audacity about 5 minutes ago and have basically no prior experience doing this, so it's 50/50 that I did all of this wrong.
I thought this claim was pretty interesting, so I wanted to try a little experiment for myself. I took a "modern" track I owned that I assumed would have some high frequency information, and did a teeny bit of analysis in Audacity for grins.
This is certainly an interesting example. Unfortunately I don't own the track and I can't exactly analyse it through youtube. The question is, are you hearing the noise floor of 16bit digital audio or are you hearing the noise floor or the studio it was recorded in or perhaps the noise floor of the microphones or other recording equipment used? I'm not sure how we'd find out.
With modern dither the noise floor of 16bit audio is even lower, so I wonder what it would sound like if that track was recorded today.
Out of interest, I used Audacity to generate a 30 second 16bit WAV of silence. I'm not sure whether Audacity applied dither to this, and if so I don't know whether the dither in Audacity is a good one anyway, but I thought i'd share the file for those interested.
Playing this file on my Denon receiver and AKG headphones, I have to turn the amp up to -10dB before I can just about hear noise. However, I can't tell you whether that noise is the noise floor of the track or the noise floor of something else in my system. I'd be interested to see how this track sounds to others.
What I can say though is I tried listening to that king crimson track (sadly through youtube) at that volume level and it while the quiet opening was listenable (fairly loud), the louder sections were almost painful.
EDIT: In an attempt to see if the noise was my system or 16bit, I generated another 30 seconds of silence and exported in 24bit. Even at 0dB on my receiver I can't hear noise with this one.
https://www.dropbox.com/s/uen66lni39xvo1j/24bit%20silence.wav
Thank you for the noise test files. Normally, to test if i could hear the 16 bit noise floor, I set my DAC to 16 bit mode, and pause a song in winamp, that way I get the DAC's output through window's kmix which adds the dither. Now I have those files, it's much more convenient (and I don't have to futz with settings on my Linux machine!). Here, I will use your tracks and compare them to listening to music.
Abstract:
Here, I'm going to ABX the empty files kraken uploaded, seeing if I can differentiate between 16bit and 24bit empty files. Then I'm going to listen to music and see if my eardrums are blown into my skull. Then I will repeat the ABX.
Materials and methods:
I listened from my CentOS linux server which has some extra fans running to keep my passively cooled raid card and all the hard disks in the machine cooled. I had a quieter listening environment in my old apartment when the server was in my bed room and I could listen in my office without my much quieter laptop+usb dac. Here, I'm using the machines motherboard line out into a Schiit Magni, and I'm using Paradox headphones with slight noise isolation. Software volumes are maxed. The schiit volume is set very loud, at about 2 o'clock. You can try and estimate the resulting SPLs using the data from this fantastic thread here. I found that the diagram of the volume pot at the bottom of the post reflects the knob on the Magni. However, I believe the sensitivity of the Paradox is less than the sensitivity listed in the thread for Fostex T50rp by direct comparison to the AKG 240s (My Paradox (modded T50rp) headphones are noticeably less sensitive than my pair of stock AKG240s, contrary to the listed data).
I played the files through foobar2000 using WINE on the centos system. Using the ABX tool, I tested whether I could differentiate the between 16bit and 24bit empty files at a specific volume setting. 30ish trials were conducted per ABX test. Then, after the ABX test, I listened to King Crimson's Lizard without adjusting the volume.
Next, I listened to the Telarc recording of Tchaikovsky's 1812 overture (and adjusting volume (lower) to accommodate the cannon blasts). Afterward, using these volume settings, I repeated the ABX of the 16bit and 24bit empty files at this lower volume setting.
Results:
Here is my foobar ABX to show whether or not I can likely discriminate between the two files:
WIthout touching the volume settings, I played King Crimson's Lizard (16/44.1). According to replayGain, the track has a peak level of 0.828 (~ -2dB) from an album with a peak of 0.99 (~0 dB). The noise in the intro sounds louder than the dither noise in the empty 16bit file, and I'm of the opinion it is tape noise (The album was recorded in 1970). At this volume setting it's definitely loud and not something I do every day, but sometimes I want to play my music loud, feel the bass, and get lost for half and hour. This is not the first time I've listened to this song at this volume.
Another track I'm fond of is the Telarc recording of the 1812 overture (24/88.2). This is a more modern recording, and the background noise is quite low, and I believe it is due to the room noise picked up by the microphones. Here, the cannons are a bit louder, especially at the end, so when I relive the climax of caddyshack, i turned the volume down a bit. According to replay gain, the track and album peak level is 0.999941 ( ~0 dB ). Here Magni was set at 12:30. Afterward, I repeated the ABX at this lower volume setting:
Conclusions:
I just wanted to point out that there are some specific, worst-case, cherry-pickable examples, where one might find the noise floor detectable and be able to listen to a track at that volume setting. If King Crimson's LIzard were recorded in a modern studio, it is plausible that the 16bit/44.1k dither noise floor could be detectable during the quietest parts of the track. It would take a track from an album with big swings in dynamics, and would only be detectable in the quietest passages while listening at otherwise very loud levels.
I'm not arguing for folks to buy hires audio. I'm asking you guys of the sound science forum to make more rigorous arguments, or to use the appropriate qualifiers on your statements, e.g., "for all practical purposes, 24 bit is unnecessary for listening" is a much better statement than "It's impossible for anyone to hear beyond 16 bit/44.1kHz". Even though redbook CD is dam near perfect for just about all audio playback situations, it only takes one single counter example, where it's slightly less than perfect to make the absolutist blanket statement false.
Let me clarify how hard the noise floor of the 16 bit track is to hear: It's really hard to hear. I didn't notice the noise until I compared it directly against the 24 bit file using the instant ABX switcher. Also, it is pretty quite here in this small midwestern city, in the middle of the night, in my office which is half under ground, in my house which is set back up and off the street. While doing the ABX, I had to pause and wait for a train to pass, and a plane to pass. It's not worth worrying about. In both tracks that I listened to, the recording noise exceeds the noise floor of the file.
Analogue noise floors and room tones are going to be higher than digital noise floors. I don't know how you differentiate between them without creating a PCM file of silence to test with.
Analogue noise floors and room tones are going to be higher than digital noise floors. I don't know how you differentiate between them without creating a PCM file of silence to test with.
kraken created a silent digital PCM file with only the dither noise in both 16 and 24 bit depths. He linked them in this thread a few posts back. These are the tracks i ABX'd before listening to some music at the same volume settings.
Of the two songs i listened to, the first was recorded in the fall of 1970. The noise was analog---I'm guessing tape. The second was a recorded performance, and im pretty certain the noise is room tones.
You turned up the silent track until you could hear the 16 bit noise floor, then played music at the same volume? Can you still hear? That must have been hella loud!
You turned up the silent track until you could hear the 16 bit noise floor, then played music at the same volume? Can you still hear? That must have been hella loud!
Noise floor refers to the level where the noise resides in the signal, obviously lower is better. In digital audio the noise floor often mainly comes from dither because it sounds better than quantisation distortion.
For people who run Windows and don't want to install any Apple software (like me), the latest version of VLC media player will play it just fine as well, though older versions (even fairly recent older versions) have trouble for some reason.
As for the second half of that file? It isn't silent. It's filled with high frequency tones. I had to turn it down (from the level at which I listened comfortably to the first half) after 10 seconds or so because it was starting to give me a headache. That having been said, I doubt it would be noticeable if you removed that part from the original, since the frequency spectrum of that second half peaks at 17-19kHz, at a level ~40dB down from the main content. Also, it looks like your filter cut it off at more like 14-15kHz rather than 12 (if not even a bit higher - the spectrum of the second half rolls off below 17kHz, while the spectrum of the first half shows substantially more 15kHz content than 17, and more 13kHz content than either), which dramatically changes the audibility, since hearing sensitivity drops off pretty steeply in that upper octave of hearing range.
Here's Bigshot's file from the last page, except converted to flac, and with the second half removed and replaced with an extremely steep high pass filtered version of the first half (-120dB at 11,500Hz, -90dB at 11,900Hz, -0.5dB at 12000Hz).
As for the second half of that file? It isn't silent. It's filled with high frequency tones. I had to turn it down (from the level at which I listened comfortably to the first half) after 10 seconds or so because it was starting to give me a headache.
Let me give you a little wake up call regarding relative proportions...
Look at the waveform. Do you see the difference between the size of the first half and the second? That gives you an idea of how much sound exists up above 12kHz. It isn't empty. You can crank the heck out of the volume and blow your ears out on those frequencies, but at normal listening volume, you ain't going to hear that stuff, particularly buried under the rest of the spectrum.
My illustration was intended to point out how unimportant the frequencies above 12kHz are to listening to music at normal listening levels, not to deny that those frequencies exist altogether. Some people think that the octave above 10kHz contributes to "treble". Not even close. Having some kind of understanding about how different frequencies contribute to music makes it a lot easier to judge quality improvements. Some things mattter a lot. Some things don't mean jack diddly.
One other quick note. Everyone talks about 12kHz and 14kHz and 16kHz as if they are miles apart. That range is less than three notes difference. "Do Re Me". 10kHz to 20kHz is about one octave. It accounts for about 10% of the full range of human hearing, and the least important part of what we hear by far.
It was an issue in the analogue age. Keeping the noise floor down low required Dolby filtering for cassette tapes, and LPs had a noise floor much higher than anything we're discussing here.
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