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Thread: Low-pass filter during DSF to FLAC conversion

  1. #1

    Join Date
    May 2020
    Posts
    5

    Low-pass filter during DSF to FLAC conversion

    Hello,

    I converted a set of DSF tracks to 24/96 PCM (FLAC) using dbPoweramp. After conversion, I analyzed the spectrum of the resulting FLAC files and expectedly found that there are lot of undesired ultrasonic frequencies above 35kHz.

    To filter these frequencies, I re-converted the DSF files, this time with applied a DSP low-pass filter set to 35kHz, which perfectly elliminated the ultrasonics from the PCM tracks. However, I found that much lower (audible) frequencies were affected as well, which was strange.

    For comparison, I post-processed the unfiltered dbPoweramp FLAC file using Audacity and its Low-pass filter effect, configured to 35kHz with steep roll-off (36db per octave). The resulting spectrogram of the audible spectrum now perfectly ressembled the original file, however without undesired ultrasonics.

    To illustrate the differences, I combined spectral fragments of these three scenarios into a single image:

    comparison.jpg

    Is this an expected behaviour from the dbPoweramp low-pass filter or I did something wrong?

    Thanks!

  2. #2
    Administrator
    Join Date
    Apr 2002
    Posts
    40,212

    Re: Low-pass filter during DSF to FLAC conversion

    We will take a look at it.

  3. #3

    Join Date
    May 2020
    Posts
    5

    Re: Low-pass filter during DSF to FLAC conversion

    Any news regarding this issue?

  4. #4
    Administrator
    Join Date
    Apr 2002
    Posts
    40,212

    Re: Low-pass filter during DSF to FLAC conversion

    We did have a look, the improvement is more of a longer term fix and will not make R17.1 which is out in the next few weeks.

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