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Topic: Lowpass Stairstep and inverted Highpass Stairstep sample (Read 4914 times) previous topic - next topic
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Lowpass Stairstep and inverted Highpass Stairstep sample

The point of these manually created low and highpass stairsteps samples is to demonstrate the following:

How much you can filter out high frequencies (lowpass) before/without it affecting the music.
How much of the actually filtered out high frequencies (highpass) you can actually hear the music in.
Unless the manual filtering was messed up the steps are at .5 second intervals and the approximate ranges are listed further below.

You may (or may not) be surprised by the results when listening to these two samples.
Myself I found that surprisingly it was not until the lowpass was around the 0-9KHz range (13 sec mark) that I began to notice a larger loss of high frequencies in the music.
Likewise it was not until the highpass was around the 11-22KHz range (11.5 sec mark) that I began to notice some very high frequency rhythmic sound.
The tests was done at my normal listening level that I usually use when listening to music.

With the volume at maximum on my system (highpass sample only, with great care to avoid damaging the ears) I found that I could notice music starting at around 12KHz (10 sec mark), but this was at levels that the lowpass sample could cause damage to the ear and thus is not a normal listening level. Also note that the frequency tipping point for you may also vary based on the equipment used and listening environment.

The conclusion to take from this (in regards to this sample) is that I could in theory apply a lowpass 0-9KHz to the song and not really feel that anything is missing, if I wanted a little margin (just in case) I guess that 12KHz would be enough. This means that 24KHz sampling rate would be enough to represent the audio. And that 48KHz (which the new Opus codec uses and many soundcards uses as well just as an example) is more than enough in this case.

The sample snippet and the song was just chosen at random (plus it is also a really cool song), it is a older song so not victim to the loudness war.
It is advised that others created similar lowpass and (inverted-)highpass samples of other types/genres/eras of music as well as the audible threshold frequencies of these two samples could be specific to this song alone and thus not representative of all music.

The stairstep was chosen as it is easier to notice quick frequency drops/rises, and half a second is short enough to allow fast drops/rises, but slow enough to allow the ear to notice it. Having the frequency high/low-pass at half a second intervals also allow the mind to quickly get into a set rhythm, which should let you home in quickly on the frequency change itself. The filter is fairly sharp but not a perfect brickwall filter, but seems to do the job well enough for this sample.

What is the lesson I learned from this simple test? That we hear a lot less than we think we do, or that certain frequencies are irrelevant to enjoy listening to music. And that once could save space/make life easier for audio codecs by applying appropriate lowpass filters prior to encoding, which in turn will help the codec use more bits where it matters and thus improve the quality of the encoding.


44KHz Samplerate, 32bit floating point, dithered to 16bit, encoded as FLAC.

Quote
The Moody Blues - Tuesday Afternoon (Lowpass Stairstep Sample)

0:00.0-0:00.5 = 0-22.0KHz
0:00.5-0:01.0 = 0-21.5KHz
0:01.0-0:01.5 = 0-21.0KHz
0:01.5-0:02.0 = 0-20.5KHz
0:02.0-0:02.5 = 0-20.0KHz
0:02.5-0:03.0 = 0-19.5KHz
0:03.0-0:03.5 = 0-19.0KHz
0:03.5-0:04.0 = 0-18.5KHz
0:04.0-0:04.5 = 0-18.0KHz
0:04.5-0:05.0 = 0-17.5KHz
0:05.0-0:05.5 = 0-17.0KHz
0:05.5-0:06.0 = 0-16.5KHz
0:06.0-0:06.5 = 0-16.0KHz
0:06.5-0:07.0 = 0-15.5KHz
0:07.0-0:07.5 = 0-15.0KHz
0:07.5-0:08.0 = 0-14.5KHz
0:08.0-0:08.5 = 0-14.0KHz
0:08.5-0:09.0 = 0-13.5KHz
0:09.0-0:09.5 = 0-13.0KHz
0:09.5-0:10.0 = 0-12.5KHz
0:10.0-0:10.5 = 0-12.0KHz
0:10.5-0:11.0 = 0-11.5KHz
0:11.0-0:11.5 = 0-11.0KHz
0:11.5-0:12.0 = 0-10.5KHz
0:12.0-0:12.5 = 0-10.0KHz
0:12.5-0:13.0 = 0-09.5KHz
0:13.0-0:13.5 = 0-09.0KHz
0:13.5-0:14.0 = 0-08.5KHz
0:14.0-0:14.5 = 0-08.0KHz
0:14.5-0:15.0 = 0-07.5KHz
0:15.0-0:15.5 = 0-07.0KHz
0:15.5-0:16.0 = 0-06.5KHz
0:16.0-0:16.5 = 0-06.0KHz
0:16.5-0:17.0 = 0-05.5KHz
0:17.0-0:17.5 = 0-05.0KHz
0:17.5-0:18.0 = 0-04.5KHz
0:18.0-0:18.5 = 0-04.0KHz
0:18.5-0:19.0 = 0-03.5KHz
0:19.0-0:19.5 = 0-03.0KHz
0:19.5-0:20.0 = 0-02.5KHz
0:20.0-0:20.5 = 0-02.0KHz
0:20.5-0:21.0 = 0-01.5KHz
0:21.0-0:21.5 = 0-01.0KHz
0:21.5-0:22.0 = 0-00.5KHz


Quote
The Moody Blues - Tuesday Afternoon (Highpass Stairstep Sample)

0:00.0-0:00.5 = 22.0-22.0KHz
0:00.5-0:01.0 = 21.5-22.0KHz
0:01.0-0:01.5 = 21.0-22.0KHz
0:01.5-0:02.0 = 20.5-22.0KHz
0:02.0-0:02.5 = 20.0-22.0KHz
0:02.5-0:03.0 = 19.5-22.0KHz
0:03.0-0:03.5 = 19.0-22.0KHz
0:03.5-0:04.0 = 18.5-22.0KHz
0:04.0-0:04.5 = 18.0-22.0KHz
0:04.5-0:05.0 = 17.5-22.0KHz
0:05.0-0:05.5 = 17.0-22.0KHz
0:05.5-0:06.0 = 16.5-22.0KHz
0:06.0-0:06.5 = 16.0-22.0KHz
0:06.5-0:07.0 = 15.5-22.0KHz
0:07.0-0:07.5 = 15.0-22.0KHz
0:07.5-0:08.0 = 14.5-22.0KHz
0:08.0-0:08.5 = 14.0-22.0KHz
0:08.5-0:09.0 = 13.5-22.0KHz
0:09.0-0:09.5 = 13.0-22.0KHz
0:09.5-0:10.0 = 12.5-22.0KHz
0:10.0-0:10.5 = 12.0-22.0KHz
0:10.5-0:11.0 = 11.5-22.0KHz
0:11.0-0:11.5 = 11.0-22.0KHz
0:11.5-0:12.0 = 10.5-22.0KHz
0:12.0-0:12.5 = 10.0-22.0KHz
0:12.5-0:13.0 = 09.5-22.0KHz
0:13.0-0:13.5 = 09.0-22.0KHz
0:13.5-0:14.0 = 08.5-22.0KHz
0:14.0-0:14.5 = 08.0-22.0KHz
0:14.5-0:15.0 = 07.5-22.0KHz
0:15.0-0:15.5 = 07.0-22.0KHz
0:15.5-0:16.0 = 06.5-22.0KHz
0:16.0-0:16.5 = 06.0-22.0KHz
0:16.5-0:17.0 = 05.5-22.0KHz
0:17.0-0:17.5 = 05.0-22.0KHz
0:17.5-0:18.0 = 04.5-22.0KHz
0:18.0-0:18.5 = 04.0-22.0KHz
0:18.5-0:19.0 = 03.5-22.0KHz
0:19.0-0:19.5 = 03.0-22.0KHz
0:19.5-0:20.0 = 02.5-22.0KHz
0:20.0-0:20.5 = 02.0-22.0KHz
0:20.5-0:21.0 = 01.5-22.0KHz
0:21.0-0:21.5 = 01.0-22.0KHz
0:21.5-0:22.0 = 00.5-22.0KHz