Filter quality

[Doobrey]

Do DAC filters have an impact on how we perceive treble quality?

For example would a filter with poor attention let in more aliasing and create a harsher sound?

 

[Hayabusa]

Depends on how the rest of the audio chain after the DAC handles the alias signal.
In theory it could increase inter modulation distortions that fold back into the audible range.
Also a speaker(tweeter) could not handle the extra high frequency energy correctly.
But if all components after the DAC are 'perfect' it should not be audible.

 

[Doobrey]

So let’s assume the rest of the chain was perfect, a “chord like” filter would be the best for the smoothest cleanest treble?

 

[NTK]

No. A reconstruction filter with poor attenuation simply means there may be more ultrasonic "garbage" above the Nyquist frequency.

 

[Doobrey]

When those artefacts fold back in to the audible signal what does it do to the sound?

 

[JSmith]

How DAC reconstruction filters would sound like if we were bats (listening examples)

There is a lot of discussion on how different DAC reconstruction filters sound like, besides the pure technical aspects which are easily explained and visualized with frequency response plots where the imaging -- mirrored frequencies above half the sample rate -- can be seen (if any), as well as...

www.audiosciencereview.com

DAC Filters

When it comes to filters, which one do you choose for the most honest and faithful reproduction? Everyone will have their own prefences but that does not mean its the closest to the source, if its even audible in the first place. How do we know which one is the most accurate?

www.audiosciencereview.com

JSmith

 

[HarmonicTHD]

When those artefacts fold back in to the audible signal what does it do to the sound?

Mainly nothing as with SOTA DAC filters are not a concern and the distortions are by orders of magnitude below audibility. To be specific: pick a DAC which was measured here and look at the multi tone test.

And the filters from the Chord company are not any better (or worse). It is just a myth the company likes to uphold to sell their products. It has been analyzed here many times.

 

[voodooless]

To be specific: pick a DAC which was measured here and look at the multi tone test.

Those are at 192 kHz, but bandwidth shown is only 20 kHz. Nothing about the reconstruction filter can be gleaned from that.

 

[NTK]

When those artefacts fold back in to the audible signal what does it do to the sound?

The D-to-A reconstruction process does not produce aliasing (fold down in frequency). I had been mistaken about that before too.

Look at D-to-A as a reverse of the sampling process. When you have components above the Nyquist frequency in the sampled signal, they alias into frequencies below Nyquist. In the reconstruction process, the signal below Nyquist "image" to frequencies (at Fs ± f, 2Fs ± f, 3Fs ± f, ... etc,.) above Nyquist.

 

[DonH56]

ADC conversion can produce aliasing of signals above Nyquist (half the sampling rate) frequency back into the signal (base) band. DACs produce images that lie above the Nyquist frequency and do not fall back (alias) into the signal band. A poor anti-imaging filter can add more high-frequency content that is objectionable, though remember it is usually above (often well above) 20 kHz so may not be audible. It could dump more power into your tweeters; whether it would be enough to cause damage seems unlikely, but not something I have really analyzed.

My signature has a link to a post with a listing of articles showing ADC and DAC operation if you want to understand aliasing and imaging better.

 

[Doobrey]

So a filterless nos DAC won’t add junk in to the audible range?

 

[voodooless]

So a filterless nos DAC won’t add junk in to the audible range?

Not junk, but they cannot reconstruct high frequencies properly. The HF droop is only half of the story.

NOS vs. Digital Filtering DACs: Exploring filtering turned off, implications, fidelity and subjective audibility. (Recent BorderPatrol DAC chatter...)

A blog for audiophiles about more objective topics. Measurements of audio gear. Reasonable, realistic, no snakeoil assessment of sound, and equipment.

archimago.blogspot.com

So what it can do is modulate high frequency content with a lower frequency. This may very well be audible in some cases. Though with real music, you’ll probably notice the frequency response error much more than the modulation.

 

[NTK]

So a filterless nos DAC won’t add junk in to the audible range?

Here is a very quick description of the D/A process (with no oversampling) from Chapter 3 of The Scientist and Engineer's Guide to Digital Signal Processing.

The "filterless NOS" conversion represents only the top 2 steps in the left ("a" and "c", time domain) and right ("b" and "d", frequency domain) figures. "Filterless" is a misnomer. The zeroth-order hold conversion (= sample-and-hold stairsteps, as shown in figure "c") is actually a convolution of the digitized samples in the form of an impulse train (figure "a") with a unit square pulse. In the frequency domain, it is the spectrum of the digitized signal multiplied by the Fourier transform of the unit square pulse, which is the sinc function (spectrum of the stairsteps = the product of the 2 curves in figure "d"). Therefore, the sample-and-hold stairsteps actually are the results of the digitized samples filtered by a filter that has a frequency response that looks like a sinc function.

To correct the frequency response errors of the filtering by the sample-and-hold process (and to remove the residual "junk" above Nyquist due to the incomplete LP filtering), the stairsteps needs to be filtered by a filter with the response that is shown in the right side third from figure "e" (the "ideal reconstruction filter"). After this filter, you'll have the proper analog signal reconstructed (figures "f" and "g"). Without this second filter, the filterless NOS produces a non-flat frequency response in addition to the inadequate removal of the "junk" above Nyquist.

 

[Hayabusa]

The D-to-A reconstruction process does not produce aliasing (fold down in frequency). I had been mistaken about that before too.

Look at D-to-A as a reverse of the sampling process. When you have components above the Nyquist frequency in the sampled signal, they alias into frequencies below Nyquist. In the reconstruction process, the signal below Nyquist "image" to frequencies (at Fs ± f, 2Fs ± f, 3Fs ± f, ... etc,.) above Nyquist.

Indeed D/A creates the images/replicating spectra but any non linear process after this can cause parts of these images fold-back in to other (also audible) frequencies.