I never got around to reviewing the last concert I attended in 2014, which consisted not only of Peter Rehberg’s first solo appearance in more than five years, but also the world premiere of Fennberg, a.k.a. Rehberg and Fennesz, as well. (I was, sadly, not in Vienna at the time Fenn O’Berg, a.k.a. Rehberg, Fennesz and Jim O’Rourke, played at Porgy & Bess in 2001, part of which was recorded for posterity as “A Viennese Tragedy” on the trio’s second album The Return of Fenn O’Berg. Legend has it that the track was so named because the audience on that occasion was so pitifully small.) Now is as good a time as any to rectify that omission, since last week Rehberg appeared again at the same venue, this time at the second of two concerts to mark the 20th birthday of the (Editions) Mego label. I didn’t bother with the first of these, but the prospect of seeing Rehberg on the same bill as Stephen O’Malley of Sunn O))) and ex-Wire man Bruce Gilbert was too good to pass up.

First, though, back to that cold evening in December. With solo sets from Rehberg and Fennesz followed by a duo performance, the concert was a gripping illustration of the continuing power and importance of Viennese electronica. Bathed in incongruous flashing lights and buckets of dry ice, Rehberg generated moments of unearthly, twilit beauty among the gravel-hard glitches and massive, pulverizing drones. The soundscape constantly shifted and evolved, seeming almost to resolve itself into warped song structures – an impression doubly reinforced when Fennesz took the stage for his own solo set. Wearing a smart suit and scarf despite the heat inside the venue, the guitarist seemed on the point of sending the audience floating off into the Donaukanal with his shimmering silver riffs and fragmentary, blissed-out tunes.

After a short interval these two legends of the Vienna experimental scene came together for the first time ever as a duo, an event that was as moving as it was historic. Fennesz left his guitar on its stand and joined Rehberg on laptop and devices, creating a music that easily resisted the monolithic and revelled instead in its own deranged beauty. A brief, lulling sample of Tears for Fears’ “Advice for the Young at Heart” added a reflective note that contrasted with the prevailing mood of brittle agitation shaped by the duo. I very much hope that this first Fennberg appearance will not also be the last; it’s a collaboration that’s far too precious to let go.

Six months later Rehberg rounded off the second (Editions) Mego 20th anniversary concert, this time with accompanying visuals by artist and frequent Mego cover designer Tina Frank. It was another excellent performance, with Rehberg’s hovering drones and frequencies finding dreamlike parallels in the flickering, coalescing images on the screen. If there’s TV in the cold reaches of outer space, this is surely what it looks and sounds like.

The evening had been billed as starting at 7.30pm, so having made the effort to be sur place at that time it was quite irritating to find a schedule posted at the door saying that the first act would not be on until 8.00pm. In the event, I needn’t have bothered. I was distinctly underwhelmed by Stephen O’Malley’s opening slot, which consisted of 45 minutes’ worth of muddy guitar riffage and effects pedal action that reverberated and recapitulated without development. I yield to none in my admiration for the mighty Sunn O))) and for KTL, O’Malley’s project with Rehberg. But this was, I’m sorry to say, very boring indeed. Bruce Gilbert’s intervening set did little to lighten my mood, so it was a relief when Rehberg and Frank came on to rescue the evening.

To finish up, a word or two on the venue. December’s concert was my first visit to Grelle Forelle, and as I was to find out, the place had set a number of psychogeographical traps for the unwary. I somehow managed to navigate my way across a thunderous highway to the approximate area where I thought the venue was, but it took a good half hour’s trudging up and down Spittelauer Lände before I was finally able to locate it. It was only when retracing my steps back to Spittelau station on the way home that I noticed the venue’s stylized fish-shaped logo painted now and again on the pavement as a directional aid, somewhat akin to the famous yellow line that runs from Barbican underground station to the Barbican Centre in London. Clearly I should have followed those logos to find the venue, although how I was supposed to know that given that I had never seen the logo before was not adequately explained. Last Friday I was a little more confident of being able to find my way, but I was still on the lookout for the little fish designs on the pavement to help me. And guess what, most of them had disappeared, leaving me floundering just as much as on the previous occasion.

What’s more, Grelle Forelle seems to be a nightclub that puts on occasional concerts, rather than a live music venue per se. This quickly became apparent from the way the venue pulled the tiresome trick of getting the live music audience in ridiculously early and then clearing them out in double-quick time in order to prepare the room for the main business of the evening, the club night. The alternative option, of putting the live music on at a civilized hour and then not having the club night at all, is something that seems not to have occurred to the management at Grelle Forelle. Which is a shame, since the venue’s acoustics, the location and (not least) the bar are all excellent. Still, there is something insulting about being politely but firmly escorted off the premises at the end of a concert and told to relocate to the outside terrace. On a warm evening in June this was not much of a hardship, but on a cold night in December it certainly was. All things considered, both these concerts should have been held at the Rhiz, which could easily have accommodated the number of people attending them.