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How to hear the digital filter difference by ears


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It is a bit difficult to hear the sound difference of digital filtering methods (sharp roll-off, slow roll-off, NOS), because the difference happens on very high frequency range. There is a method to enhance the sound difference to hear by ears clearly: shift sound pitch by 15vb (2 octaves) to move it to hearing range.

 

Equipment used

  • RME ADI-2 Pro as DAC, XLR analog line-out, it has several different digital filter settings.
  • RME Babyface Pro as ADC, XLR analog line-in 1.

 

Sound file used

 

It is my original recorded sound of a bar chime, using AKG C414 XLS, Babyface Pro, 24bit 96kHz 1ch PCM.

barchime2496.flac

 

Original file down-sampled to 24bit 44.1kHz using sox "sox barchime2496.wav barchime2444_sox997.wav rate -b 99.7 44100"

barchime2444_sox997.flac

 

Experiment Procedure

  • Play the sound "barchime2444_sox997" with a DAC with various digital filter settings.
  • Record the analog line-level sound with ADC to create 192kHz 24bit PCM.
  • Open recorded wav file with your favorite binary editor and edit the WAV header part "SampleRate" from 192000 (0x2ee00) to 48000 (0xbb80) and "ByteRate" from 576000 (0x8ca00) to 144000 (0x23280) and save it as different file. N.B. WAV header integer values are stored as little-endian byte order. (Fig.1 and Fig.2)
  • Play the resulted files and compare the sound by ears.

 

Sound files for listening comparison
 

Played barchime2444 with RME ADI-2 Pro "Sharp digital filter", record it as 192kHz 24bit PCM then shift the pitch by 15vb.

2444adi2Sharp_24192babyface_15vb.flac

 

Played barchime2444 with RME ADI-2 Pro "Slow digital filter", record it as 192kHz 24bit PCM then shift the pitch by 15vb.

2444adi2Slow_24192babyface_15vb.flac

 

Played barchime2444 with RME ADI-2 Pro "NOS digital filter", record it as 192kHz 24bit PCM then shift the pitch by 15vb.

2444adi2NOS_24192babyface_15vb.flac

 

Original file, pitch shifted by 15vb.

barchime2496_15vb.flac

 

before.thumb.png.7bc1b28c0f6179e81287491d0767d209.png

Fig.1 Find "SampleRate" and "ByteRate" of WAV header.

 

after.thumb.png.5097759061b8e1bf7cab0bfb000b746f.png

Fig.2 Divide the values by 4 to create 15vb files for listening comparison.


original_2496.thumb.png.c75a094260ec7c3386897fd8a8294a8c.png

Fig.3 "barchime2496.flac" original recorded sound spectrogram. 32kHz or above frequency exhibits the distortion of the microphone, therefore it is attenuated using Adobe Audition.

 

original_2496_4x.thumb.png.9177ac4b9600ebc0ced77d2f683ca2e2.png

Fig.4 "barchime2496_15vb.flac", Playback time becomes 4x longer and all signal frequency becomes 4x lower.

 

2444.thumb.png.a6d34d39f606ce7aa13d76e0ba9e2152.png

Fig.5 "barchime2444_sox997.flac", original file downsampled to 24bit 44.1kHz PCM. Notice 22.5kHz or above signal is deleted by downsampling.

 

rec_sharp.thumb.png.cabfcfd678f30ab28be30b3e55b05847.png

Fig.6 Sharp roll-off digital filter. This is a text-book digital filter. The information stored on the file "barchime2444_sox997.flac" is outputted faithfully. Vertical axis range is now becomes 0 to 96kHz because recording sample rate is 192kHz.

 

rec_NOS.thumb.png.2a811b957c48c3ef40fe98bf24c4f4a7.png

Fig.7 NOS (zero order hold) digital filter. Notice the aliasing noise above 22.05kHz, the frequency range 22.05kHz to 44.1kHz is vertically flipped image of 0 to 22.05kHz and 44.1kHz to 66.15kHz is vertically flipped image of 22.05kHz to 44.1kHz and so on. those signal is not found on playback file nor the original 96kHz recorded file, so it is unwanted noise IMO. The aliasing noise sound can be very annoying because its frequency is not related to the original signal, but it is not awful very much in this example sound.

 

rec_slow.thumb.png.573b6cc2e166658de131c601084011a5.png

Fig.7 Slow roll-off digital filter. Notice the aliasing noise above 22.05kHz. The aliasing noise is visible (above 22.05kHz), its amount is smaller than NOS. Notice the aliasing noise signal is not related to the original signal of harmonics.

 

Sunday programmer since 1985

Developer of PlayPcmWin

Link to comment
  • 2 months later...
On 2/19/2022 at 5:35 AM, yamamoto2002 said:

It is a bit difficult to hear the sound difference of digital filtering methods (sharp roll-off, slow roll-off, NOS), because the difference happens on very high frequency range. There is a method to enhance the sound difference to hear by ears clearly: shift sound pitch by 15vb (2 octaves) to move it to hearing range.

 

Equipment used

  • RME ADI-2 Pro as DAC, XLR analog line-out, it has several different digital filter settings.
  • RME Babyface Pro as ADC, XLR analog line-in 1.

 

Sound file used

 

It is my original recorded sound of a bar chime, using AKG C414 XLS, Babyface Pro, 24bit 96kHz 1ch PCM.

barchime2496.flac 1.09 MB · 14 downloads

 

Original file down-sampled to 24bit 44.1kHz using sox "sox barchime2496.wav barchime2444_sox997.wav rate -b 99.7 44100"

barchime2444_sox997.flac 625.17 kB · 17 downloads

 

Experiment Procedure

  • Play the sound "barchime2444_sox997" with a DAC with various digital filter settings.
  • Record the analog line-level sound with ADC to create 192kHz 24bit PCM.
  • Open recorded wav file with your favorite binary editor and edit the WAV header part "SampleRate" from 192000 (0x2ee00) to 48000 (0xbb80) and "ByteRate" from 576000 (0x8ca00) to 144000 (0x23280) and save it as different file. N.B. WAV header integer values are stored as little-endian byte order. (Fig.1 and Fig.2)
  • Play the resulted files and compare the sound by ears.

 

Sound files for listening comparison
 

Played barchime2444 with RME ADI-2 Pro "Sharp digital filter", record it as 192kHz 24bit PCM then shift the pitch by 15vb.

2444adi2Sharp_24192babyface_15vb.flac 2.09 MB · 14 downloads

 

Played barchime2444 with RME ADI-2 Pro "Slow digital filter", record it as 192kHz 24bit PCM then shift the pitch by 15vb.

2444adi2Slow_24192babyface_15vb.flac 2.15 MB · 13 downloads

 

Played barchime2444 with RME ADI-2 Pro "NOS digital filter", record it as 192kHz 24bit PCM then shift the pitch by 15vb.

2444adi2NOS_24192babyface_15vb.flac 2.66 MB · 13 downloads

 

Original file, pitch shifted by 15vb.

barchime2496_15vb.flac 1.09 MB · 16 downloads

 

before.thumb.png.7bc1b28c0f6179e81287491d0767d209.png

Fig.1 Find "SampleRate" and "ByteRate" of WAV header.

 

after.thumb.png.5097759061b8e1bf7cab0bfb000b746f.png

Fig.2 Divide the values by 4 to create 15vb files for listening comparison.


original_2496.thumb.png.c75a094260ec7c3386897fd8a8294a8c.png

Fig.3 "barchime2496.flac" original recorded sound spectrogram. 32kHz or above frequency exhibits the distortion of the microphone, therefore it is attenuated using Adobe Audition.

 

original_2496_4x.thumb.png.9177ac4b9600ebc0ced77d2f683ca2e2.png

Fig.4 "barchime2496_15vb.flac", Playback time becomes 4x longer and all signal frequency becomes 4x lower.

 

2444.thumb.png.a6d34d39f606ce7aa13d76e0ba9e2152.png

Fig.5 "barchime2444_sox997.flac", original file downsampled to 24bit 44.1kHz PCM. Notice 22.5kHz or above signal is deleted by downsampling.

 

rec_sharp.thumb.png.cabfcfd678f30ab28be30b3e55b05847.png

Fig.6 Sharp roll-off digital filter. This is a text-book digital filter. The information stored on the file "barchime2444_sox997.flac" is outputted faithfully. Vertical axis range is now becomes 0 to 96kHz because recording sample rate is 192kHz.

 

rec_NOS.thumb.png.2a811b957c48c3ef40fe98bf24c4f4a7.png

Fig.7 NOS (zero order hold) digital filter. Notice the aliasing noise above 22.05kHz, the frequency range 22.05kHz to 44.1kHz is vertically flipped image of 0 to 22.05kHz and 44.1kHz to 66.15kHz is vertically flipped image of 22.05kHz to 44.1kHz and so on. those signal is not found on playback file nor the original 96kHz recorded file, so it is unwanted noise IMO. The aliasing noise sound can be very annoying because its frequency is not related to the original signal, but it is not awful very much in this example sound.

 

rec_slow.thumb.png.573b6cc2e166658de131c601084011a5.png

Fig.7 Slow roll-off digital filter. Notice the aliasing noise above 22.05kHz. The aliasing noise is visible (above 22.05kHz), its amount is smaller than NOS. Notice the aliasing noise signal is not related to the original signal of harmonics.

 

 

NOS absence of digital filter is often an audible problem. It causes potentially high-in-level images that can intermodulate into the audible range, plus frequency response fall-off, also within the audible range. Some DACs (like RME ADI-2) support a NOS-like filter but provide a frequency fall-off compensation. But that still doesn't address the images or their possible IMD interaction.

 

I do like your method of adjusting the sample rate! Easy enough to do. With DeltaWave app, I implemented a frequency-domain adjustment that allows one to shift frequencies from higher to lower range by an arbitrary amount and then listen. It is interesting to hear what type of sounds/noise/patterns are contained above the audible range.

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