AV Receiver Reviews

The SDR-38 includes all of Dirac Live's features at no extra cost. These include either full or limited range equalization plus the newest Dirac Live feature: Bass Control. According to Dirac: "Dirac Live Bass Control leverages all-pass filters, plus machine learning and artificial intelligence, to calculate gains, delays, and all-pass filters for each subwoofer. In this way, the Dirac solution ensures that low frequencies add up so that not only the average is controlled, but most importantly, seat-to-seat variation is minimized as we can now achieve a level of control in multiple locations at once." Dirac's Bass Control can also enhance bass performance, particularly with more than two subwoofers. (As noted earlier, for this review two SVS subs, while separately positioned, were here driven together as a single bass source.)

Unlike its more widely available room EQ competitors, Dirac Live adjusts for both amplitude and phase (time domain). It performs calculations in the Dirac Live app running on your networked computer, either a Mac or a PC. You can either create your own target curve, use a built-in target curve, or accept the latter and modify it. Once done, you export the result to the AVR, which can store three different Dirac setups plus bypass.

To shorten a very long story, after much weeping and gnashing of teeth (including a needed update to a more recent OS for my MacBook, plus lots of help from JBL), I was finally able to engage the Dirac Live program to generate a room EQ curve that looked promising—the basic target curve with a 5dB bump-up below 100Hz. But the results sounded awful: wooly bass, including a peak of over 10dB at 20Hz (above a reasonable level at 30Hz) and rolled-off highs.

The following days were a whirlwind of failed setup attempts and ergonomic gotchas, such as Dirac's channel-level setup menu, which is designed to set each channel's gain to a level that Dirac can deal with. These settings were sensitive and didn't always work without flashing a "clipping" or "low S/N ratio" warning. The uncalibrated microphone included with the JBL also aroused my suspicions as a possible cause of the poor initial results. Dirac recommends a fully calibrated mic, such as the relatively affordable miniDSP UMIK-1, but JBL doesn't include one—likely because most SDR-38s will be set up by professional installers who already own a calibrated mic.

With further help from JBL I was able to swap out the included mic for the calibrated microphone from my Dayton Audio Omnimic measurement system. After another difficult round or three with those dicey level settings, the system finally clicked into place. I achieved a good, usable setup beginning with the selectable Harman target curve, adding a small bump-up in the bass below 100Hz (rising to a maximum of about 4dB at and below 30Hz), and moved it into one of the JBL's three Dirac memory slots.

The result was worth the long slog. After making some minor tweaks via the tone controls—seldom more than +1dB in the treble and –2dB in the bass (perhaps that bass bump-up I dialed into the target curve was a bit too much) the sound in my room ended up being exceptional.

Performance
I started out my evaluation with Dirac Live disabled. In my listening space, the main issue I need to address is excessive response from 100-200Hz, and a combination of tweaking the JBL's bass control, adjusting the total level of the subwoofers, and fine-tuning the on-board EQ controls of the SVS subs, achieved an excellent measured result.

Following that, I began my serious pre-Dirac listening with Oblivion, a movie with a Dolby Atmos soundtrack I'm very familiar with. Following the opening narration, the title hits the screen accompanied by a huge musical crescendo. The JBL didn't disappoint here, filling the room with explosive power and immediately validating that its onboard amps were up to the task.

The hits continued throughout Oblivion, and not only in the loudest bits. Dynamic punch was never in doubt, but it was the quiet moments where the SDR-38 impressed me the most. To be fair, I've never been disappointed when watching this movie with other good AVRs, but the result here was certainly up there with the best of them—and perhaps marginally better.

The Greatest Showman is another frequent visitor to my 4K disc player, and it sounded every bit as impressive with the JBL, though in a different way. Music is a dominant element on both these films, but while it's heavily atmospheric on Oblivion, it's more generic here. The musical numbers sounded spectacular, with solid, deep bass, uncolored vocals, and silky, clean highs.

After finally achieving a successful Dirac Live calibration (plus some minor tweaking of the JBL's bass and treble controls), I listened to some of my favorite stereo music cuts with Dirac enabled. Deep bass in classical organ music, electronica of all sorts, and percussion-heavy cuts sounded consistently right at any volume my ears could tolerate.

I won't say that all (or even seven) veils were lifted by Dirac Live, but details I'd never noticed before were revealed on some of my favorite test recordings. (Yes, that claim has previously been made by too many reviewers in too many reviews of too many products.) But the masking of detail in recordings by room anomalies (most of them in the mid and upper bass) is a real thing, and Dirac Live succeeded in removing those.

Switching to movies, Oblivion sounded every bit as good as before and perhaps just a little more open due to Dirac's precise rendering of the mid-bass, while the opening foot stomps from the bleachers in The Greatest Showman were deeper and tighter with Dirac than without. In the Jenny Lind concert scene, the chatter of the audience before her performance was now audible as separate voices, and her voice was clear and clean (though nothing can save a 21st century pop tune from sounding crazily anachronistic in a mid-1800s setting!).

Blade Runner 2049 is among the best Atmos soundtracks, if not the best. Aided by Dirac, the crisp bass transients in its opening scene rattled the walls of my room and continued as agent K went on his mission to "retire" a fellow replicant. The atmosphere was enveloping, whether K searched the bowels of an abandoned factory for a model horse (accompanied this time by a now groaning, ominous bass), or fought another adversary in an old Las Vegas nightclub while surrounded by an audio-video hologram of an old Vegas show.

One troubling flaw kept cropping up both with and without Dirac. The SDR-38 would mute the opening fraction of a second of sound on the first track of a recording, and a millisecond or so of sound would also go missing if I manually selected a different chapter or track. Hopefully, this is something JBL can fix in a firmware update.

I had one other troubling issue with the SDR-38: On my last day working on this review I made a final attempt at a Dirac Live calibration using Wi-Fi, but his time didn't go past the microphone setup page as I was merely checking for a connection. But later when I looked back at the setup menus, all three of the Dirac calibrations I had saved in memory (including the good one) were gone! That's something that shouldn't happen.

Conclusion
You can spend a lot less than the $8,550 JBL Synthesis charges for the SDR-38 and get a feature-packed AVR that offers admirable performance. Also, the SDR-38's oddities and possible bugs need to be addressed before I can recommend it without reservation. Having said that, when things were going well, the SDR-38's overall performance left me deeply impressed, and its Dirac Live processing counts among the best room EQ solutions available.