Apologies, I should've really just said that he had a vested interest in it.
Either way, the people that came to the presentation didn't come to hear about the product he was promoting - we wanted, at least I wanted, to hear the ideas in his book. Instead we got the old switcheroo.
I say this because back when I used to frequent Marginal Revolution, I found that there was a good deal of self-promotion of Cowen's work in the website - for example, he would link an interesting news story and provide minimal commentary, but then would link his tangentially related research. I understand his incentive for doing this, but the amount of self-promotion was enough to annoy me and make me stop reading.
Years later, I attended a presentation that Cowen gave that was ostensibly on his book the Great Stagnation, but in reality it turned out to be a demonstration of some online learning venture he was bankrolling at the time.
He's a smart and productive guy, no doubt, but my (anecdotal) experiences make me wonder about what is behind an article like this.
There were a few programs that I used in the past to write and playback my own tabs.
The main program I used was TuxGuitar [1]. I felt it suited my purposes - I could work out the rhythm and positioning with this program and play files in various formats. The sound quality and features were adequate - sort of a low-fi MIDI sound where different timbres and instruments could be selected. It looks like it may not be a maintained product, but the source is available if you want to tinker with it [2].
Another program that my friends used to use is Power Tab. The original programs look to be abandoned, but it seems that an open-source implementation is actively maintained here. [3]
There is a commercial product called Guitar Pro, but I felt the open-source packages were good enough. Guitar Pro also had an active community (maybe it still does), and many users would contribute their own tabs in Guitar Pro's file format (.gp3, .gp4, etc.) which I would read and edit with TuxGuitar. It used to be pretty easy to find these files available online, but I suspect copyright holders cracked down on these communities much like they did with OLGA.
I don't understand what is being used as the denominator to generate this 1/3 number in the headline. A quick search shows that the US MBS market is about $10.3 trillion in size [1] - the actual mortgage market is larger (what nostromo mentioned earlier). Putting some recent numbers [2] over the size of the MBS market would show that the Fed owns a little less than a 1/5 of all US MBS.
Also, he mentions that the Fed has been purchasing roughly $100 billion per month in MBS securities since April, but this leaves out the fact that a non-insignificant number of MBS in their holdings are either i) reaching maturity, or ii) being prepaid. The second issue is more prevalent now - with the low-rate environment that exists in the US many people are refinancing their mortgages to take advantage of lower rates, but in any case it isn't uncommon for mortgages to be paid off before their maturity date. I don't know what the net figures are, but what I'm trying to say is that purchases of MBS != growth of MBS holdings.
I seriously think this author has somehow conflated the size of the SOMA assets with the size of the MBS market - continuing growth of MBS at $100 billion for the rest of the year, leaving all else equal, will give us about $2.4 trillion of MBS over a denominator of $7.4 trillion - which would give us about 1/3.
Either way, the people that came to the presentation didn't come to hear about the product he was promoting - we wanted, at least I wanted, to hear the ideas in his book. Instead we got the old switcheroo.