1. WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Invitation: Audible intersample clipping test

Discussion in 'General Audio Discussions' started by bennetng, Jan 12, 2018.

  1. bennetng

    bennetng Member

    Joined:
    Nov 15, 2017
    Messages:
    46
    Likes Received:
    4
    The test signal is attached at the end of this post:

    https://forum.cockos.com/showthread.php?t=201868

    Basically I don't like the idea of blaming those who make music or DACs for intersample clipping since there is no absolute clipping point. My test signal is a bit more sophisticated than the one used in TC Electronic and Benchmark's article/paper. I realize members in ASR like measurements so you are also encouraged to measure your equipment with my test signal.

    Thanks.
     
  2. amirm

    amirm Founder/Admin CFO (Chief Fun Officer) Staff Member

    Joined:
    Feb 13, 2016
    Messages:
    9,339
    Likes Received:
    1,454
    Location:
    Seattle Area
    I will test later when I am in my lab. Then again, for grins i tried to play it on my laptop speakers and it created tinnitus in my ears like I have never heard! And I could hear/sense very high pitch sound. I started at low volume and went nuts after just a few seconds and at low volume no less!!!

    Looking at the spectrum, I see there is a sum of three high frequency tones. I am concerned about hearing damage for members. Is there a reason you picked such high frequency components?

    upload_2018-1-12_6-37-6.png


    I am very interested in this type of test though. :)
     
  3. RayDunzl

    RayDunzl Major Contributor Central Scrutinizer

    Joined:
    Mar 9, 2016
    Messages:
    3,958
    Likes Received:
    633
    Location:
    Riverview, Fl
    4.66dB over...

    Nice trick...

    upload_2018-1-12_9-53-53.png
     
  4. bennetng

    bennetng Member

    Joined:
    Nov 15, 2017
    Messages:
    46
    Likes Received:
    4
    The test signal is aimed at adding sample points in a continuous and audible (if clipped) way after upsampling, either by a software upsampler or a hardware DAC. Here is a screenshot of original (right) and 4x upsampling (left).

    Yeah. Ray's response is very fast. Thanks.
    4x.png
     
  5. RayDunzl

    RayDunzl Major Contributor Central Scrutinizer

    Joined:
    Mar 9, 2016
    Messages:
    3,958
    Likes Received:
    633
    Location:
    Riverview, Fl
    I see 4.66dB overs in your test file, which seems to invalidate (maybe) this blurb about "worst case" from Benchmark:

    "It is possible to build interpolators that will not clip or overload, but this is not being done by the D/A and SRC chip manufacturers. For this reason, Benchmark has moved some of the digital processing outside of the D/A chip. In the Benchmark DAC2 and DAC3 converters we have an external interpolator that has 3.5 dB of headroom above 0 dBFS. This means that the worst-case +3.01 dBFS intersample peaks can be processed without clipping."

    https://benchmarkmedia.com/blogs/application_notes/intersample-overs-in-cd-recordings
     
  6. bennetng

    bennetng Member

    Joined:
    Nov 15, 2017
    Messages:
    46
    Likes Received:
    4
    I am not a Benchmark hater (or fanboy). The reason for making this test signal is to prove that it is possible to make audible intersample peaks with relatively high values.

    I know some people for example believe that replacing the CR2032 cell on a PC motherboard to another brand can improve sound quality but don't believe intersample peaks. They think reducing volume in digital domain harms bit-perfectness.

    Just reduce the playback volume of your playback software then you don't need a Benchmark.
     
  7. Blumlein 88

    Blumlein 88 Major Contributor

    Joined:
    Feb 23, 2016
    Messages:
    2,361
    Likes Received:
    663
    That is a potentially tweeter busting test signal.

    We have discussed this some here before only using white noise. Don has shown it is possible to get intersample overs of around 10 db at times.

    We used some white noise in the other thread where this was discussed. I use -4db white noise in setting levels for testing. It is around - 4db in my experience where these overs mostly go away though you still get some. At higher levels you get plenty some being rather high in level. If you run high level white noise long enough you'll have to reduce to about -10 db to get none.

    Our method in the other thread was to create long files of white noise and oversample them 8 times in software. Benchmarks decision on how much to reduce the level to prevent these mirror my own idea that -4db is a good choice. 3.5 to 4 db reduction gets rid of nearly all you might encounter with synthetic signals. While it doesn't mean no natural signal couldn't cause an over at that point it becomes very, very rare. Rare enough it will not be an on going issue to cause sound quality differences listening to music.

    Most IS overs in music are caused by processing usually involving limiting.
     
  8. bennetng

    bennetng Member

    Joined:
    Nov 15, 2017
    Messages:
    46
    Likes Received:
    4
    I tried a noise-based test signal in the same forum:
    https://forum.cockos.com/showthread.php?t=193559

    DAW users usually don't manually upsample their files to find ISP, they use BS.1770 compliant "True Peak" meters which aimed at estimate the performance of hardware DACs rather than resamplers. Some resamplers are overly accurate at near Nyquist and result in higher peaks.

    Here is my analysis of that noise signal with a resampler with different quality settings and two DACs.
    https://forum.cockos.com/showpost.php?p=1863978&postcount=61

    While using noise as test signal can yield higher peaks, clipping distortion cannot be measured or heard in the audible band, and that's why I made another test signal. The highest tone in my signal is lower than 18kHz, which means lower than the typical 19+20kHz test signal. Also my signal has a fade-in stage so unless the test signal is being played unattended, users have enough time to reduce the playback volume.
     
  9. Soniclife

    Soniclife Active Member

    Joined:
    Apr 13, 2017
    Messages:
    144
    Likes Received:
    23
    Location:
    UK
    Is there software you could run your music library through to look for the max real world example?
     
  10. bennetng

    bennetng Member

    Joined:
    Nov 15, 2017
    Messages:
    46
    Likes Received:
    4
    Yes. foobar2000 support BS.1770 and EBU R128 standard with oversampled "true peak" and "LU" (a replacement of VU) loudness scanner. You can scan and manually edit the desired playback level and they will be saved as metadata in your audio files.

    BS.1770 suggests 4x upsampling for 44/48k contents and 2x upsampling for 88/96k contents to detect "true peaks" and has a reference algorithm. 176.4/192k or above are not required to be upsampled.

    To enable oversampled peak detection, go to foobar2000's preferences and set the Peak scan oversample factor to at least 2.

    ReplayGain is a widely used standard in various audio players (check Wikipedia). It stores Track peak and Album peak as metadata in audio files. Track peak is the peak of individual audio file and album peak is the highest peak of an album. In this way users can maintain the relative loudness of an album during playback.

    The peak values are stored as floating point numbers and 1.0 means 0dBFS or 0dBTP if oversampled scanning is enabled. For example there is a track with 1.387928 in my screenshot, copy and paste the following line in google:

    20*log(1.387928)

    Which means +2.847...dBTP

    in foobar2000 and other ReplayGain compliant players, you can specify the audio player to reduce the playback level according to the scanned track peak or album peak.

    The "Preamp" section sets a target loudness in terms of LU. By default foobar2000 uses -18LUFS as target but as you can see, there are sliders for you to adjust. With the "prevent clipping according to peak" option selected, even if you set the slider all the way to the right, files with RG info won't clip, but in this way the target loudness cannot be maintained.
    replaygain.png replaygain2.png
     
    Soniclife and Blumlein 88 like this.
  11. Soniclife

    Soniclife Active Member

    Joined:
    Apr 13, 2017
    Messages:
    144
    Likes Received:
    23
    Location:
    UK
    That's great, will it sort by track peak to find the max in your collection?
     
  12. bennetng

    bennetng Member

    Joined:
    Nov 15, 2017
    Messages:
    46
    Likes Received:
    4
    Select several tracks in the playlist and right-click > ReplayGain > scan selection as a single album. For example you selected 5 tracks and they have track peaks like these:

    1.1
    0.8
    0.9
    1.2
    0.7

    Then the album peak will be automatically 1.2. There is no need to manually find the highest peak yourself.
     
Loading...

Share This Page