Are Reconstruction Filters Audible? (Part 2)

In part one I gave an overview of what a digital reconstruction filter is, why it’s necessary and how it might be responsible for some of digital audio's flaws.

I also stated that I could, in fact, hear the difference. Since not everyone agrees that linear phase filters are audible, I thought i would explain why I believe I can.

About 10 years ago or so, a friend of mine -- and audio engineer of some repute -- told me he was convinced filters were part of what was wrong with digital audio. He had been talking to a team in Europe that was working on more advanced filters and thought they were making headway.

He also put together -- and this was possibly one of only a few in existence at the time -- a DAC where the filter could be selected via a remote, on the fly.

I met up with him while he was visiting friends in Bangkok and we went to a mutual friend’s loudspeaker factory that had a dedicated listening room. We demoed music and he switched the filter periodically and asked us what we thought.

As much as I accepted the idea on an intellectual level, it was very hard for me to say that there was a difference -- and I certainly could not have identified one filter vs another.

Fast forward a decade or so. In that decade I had all but abandoned audio as a hobby. But the industry had been paying attention to people like my friend and it had become common for DACs to have selectable filters.

This is a big deal. It required buy-in of the idea both by IC manufacturers and by the companies producing end products for consumers. Implementing additional filters at the hardware level is certainly non-trivial, incurring significant R&D and fabrication costs.

Now the fact that the industry added support for other filter types does not necessarily mean that they’re audible -- they could have been simply following market demand. Markets are not always rational.

My New Rig

For reasons I can’t remember i decided in the middle of the night to get a nice headphone rig. After a number of reviews and recommendation lists I decided on getting Beyerdynamic's flagship T1.

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This is not an inexpensive headphone, but I had a horrible experience with a "budget" set of AKM over ear headphones. (They basically disintegrated after a year and never sounded that good to begin with.) I decided that I would get a no-compromise set this time around. The T1s don't have the flattest frequency response but they've got a large driver with a powerful motor (T1 stands for one tesla of magnetic flux) and the build quality is exceptional.

These are power hungry headphones at 600 ohms, so I looked around for powerful, possibly balanced DAC/AMP combos. I'm not sure there's any real magic in balanced heaphone amps, other than the fact that it doubles the voltage swing. For high impedance headphones, more voltage means more power since they're voltage- and not current-limited.

I decided to pick up a DAC and a separate AMP from Schiit audio. After a few days, Schiit emailed me to tell me my order had been unceremoniously canceled because I was obviously trying to commit fraud?

After an unpleasant exchange with their head of sales, I was told that all orders to Thailand had to be made via a verified PayPal account (which was stated nowhere on their payment page).

I can't speak for anyone else, but I don't use PayPal because I'm an adult. I've found that Citibank is welcome everywhere in the world. I've been using the same card at the same address for years and I've never had an issue with "fraud" before.

I guess a little racism is to be expected from a company who's main selling point is "made in America, not Asia". The irony, of course, is that probably most of the tools, computers, etc. used to design their products were made in China. Made in China is hardly associated with lower quality. Maybe it was in the past; it's certainly not today.

My recommendation: Do not buy Schiit.

Anyway, it turns out that DAC/AMP combos that can drive high impedance headphones are not that common, but I found another that ticked all of my boxes: Questyle's CMA400i.

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I had never heard of the company or the product, but it had solid reviews and I liked what they prioritized in their design. So, without having a chance to hear it in person I took the plunge. The local distributor had it delivered by messenger within a couple hours.

Since the universe obviously wants me to listen to music, my headphones were delivered several days ahead of schedule and arrived the same day.

And wow! The combo was really good. I'm not sure where Beyer manufactures its headphones (good chance it's in China) but the CMA400i is proudly designed in China and manufactured at Foxconn, along with Apple products and probably scores of other premium consumer electronics.

So my re-introduction to audio turned out to be very satisfying and started me down the rabbit hole of what improvements had been made on the software side of playback.

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