Joe Bloggs
Sponsor: HiByMember of the Trade: EFO Technologies Co, YanYin TechnologyHis Porta Corda walked the Green Mile
A look at lowpass filter ringing, as occurs in "low-res" audio playback (in this case 44.1kHz):
1. An ideal impulse at high sample rate (352.8kHz) https://www.dropbox.com/s/m7jk56jj2r4o6wh/352800-impulse.wav?dl=0
Waveform plot
Frequency response plot
2. Lowpassed to 44.1kHz, with classic ringing tails caused by lowpass filter https://www.dropbox.com/s/cmwsht528pnaqke/44100.wav?dl=0
Waveform plot (linear interpolation)
Waveform plot (smoothed)
Eyeballing the plot, the oscillation frequency of the ringing is close to Nyquist, (22.05kHz, 1 cycle in 2 samples) but how to quantify this?
Frequency analysis of the impulse shows flat response up to 20500Hz or so.
3. Same as (2), but subtracted by an ideal impulse in the middle. We see that the main pulse of the lowpassed impulse is cancelled out to blend in with the ringing before and after--this lets us analyse the ringing in isolation. https://www.dropbox.com/s/ufq98h0ajblfxtk/44100-ringing%20only.wav?dl=0
Waveform plot (linear interpolation)
Waveform plot (smoothed)
Frequency analysis of the modified impulse confirms that the main impulse has been cancelled out (down to over -200dB) while the ringing that remains is confined to over 20000Hz.
4. Same as (3), but with amplitude amplified to within 0.2dB of full scale. The file from (3) may be used to gauge audibility of ringing in normal program material with your player set to the same volume at which it normally plays music; this file is "can you hear this ringing with the volume turned up to 11 in the sound file?" https://www.dropbox.com/s/6fexu9byxw2ejz2/44100-ringing%20only-amplified.wav?dl=0
1. An ideal impulse at high sample rate (352.8kHz) https://www.dropbox.com/s/m7jk56jj2r4o6wh/352800-impulse.wav?dl=0
Waveform plot
Frequency response plot
2. Lowpassed to 44.1kHz, with classic ringing tails caused by lowpass filter https://www.dropbox.com/s/cmwsht528pnaqke/44100.wav?dl=0
Waveform plot (linear interpolation)
Waveform plot (smoothed)
Eyeballing the plot, the oscillation frequency of the ringing is close to Nyquist, (22.05kHz, 1 cycle in 2 samples) but how to quantify this?
Frequency analysis of the impulse shows flat response up to 20500Hz or so.
3. Same as (2), but subtracted by an ideal impulse in the middle. We see that the main pulse of the lowpassed impulse is cancelled out to blend in with the ringing before and after--this lets us analyse the ringing in isolation. https://www.dropbox.com/s/ufq98h0ajblfxtk/44100-ringing%20only.wav?dl=0
Waveform plot (linear interpolation)
Waveform plot (smoothed)
Frequency analysis of the modified impulse confirms that the main impulse has been cancelled out (down to over -200dB) while the ringing that remains is confined to over 20000Hz.
4. Same as (3), but with amplitude amplified to within 0.2dB of full scale. The file from (3) may be used to gauge audibility of ringing in normal program material with your player set to the same volume at which it normally plays music; this file is "can you hear this ringing with the volume turned up to 11 in the sound file?" https://www.dropbox.com/s/6fexu9byxw2ejz2/44100-ringing%20only-amplified.wav?dl=0
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