Automated Processes, Incorporated, popularly known as API, has a rich history spanning over half a century. Since their first consoles were installed in 1967, API has developed new technologies, established important pro audio standards, and contributed to the production of many great records. Building on this legacy of audio excellence, they have recently introduced the ASM164, an analog summing mixer featuring 16 inputs with two stereo buses and a signal path based on the design of The Box console [Tape Op #101].
On first look, you will notice the rows of extruded aluminum knobs with colored centers set against the matte black panel of the ASM164. The level controls are detented attenuators that ensure matching, while the pan pots move smoothly with moderate resistance and have a solid center detent. The A and B bus switches are amber LED push-buttons, making it easy to identify their status, and the insert (INS) switches illuminate green when engaged. The icing on the cake is the pair of lighted analog VU meters, which adds to the visceral experience. It has the feel of a classic console in a small two rack space unit package.
What distinguishes the ASM164 is the 2520 op-amp and transformer output design that adds coloration and imparts the signature API sound, which is often described as warm and musical. These are fairly vague descriptions, and so to better understand these sonic characteristics, I conducted listening tests using a range of material, including ‘60s and ‘70s classics, indie, hip-hop, and electronic tracks. Throughout these sessions, it was discovered that certain elements, regardless of genre, are enhanced in specific ways.
The first test involved a classic rock session with stems for vocals, bass, drums, accompaniment, and backing vocals. To establish a baseline for comparison, I set up a mix in Apple Logic Pro [Tape Op #74] with panning and level adjustments. The tracks were then routed to the ASM164 as stereo pairs, and I engaged the 0 dB BYP button to set all inputs to unity gain. Immediately, the mix felt noticeably different. Everything seemed closer to the listening position, and vocals were especially more upfront. The bass track was panned off-center, and its position was distinguishable in the DAW mix. Through the API, the bass felt larger and occupied a bit more of the center. Drums exhibited a richer midrange presence, as did guitars, which also projected forward in the mix. For comparison, I ran the same session through a different summing mixer known for transparency. This mix had more spatial detail but lacked the pronouncement of the ASM164 mix.
To hear how the ASM164 sounds on a modern track, I set up a hip-hop session for testing. The vocal stems, heavily processed with Antares Auto-Tune [Tape Op #126] and compression, still popped up front and revealed more midrange detail. Additionally, transients of the programmed drum parts also exhibited a bit more crispness. Additionally, this track provided an opportunity to push things a bit and see how driving the summing bus with heavy Roland TR-808 bass drums would sound. The VU meters started pegging pretty severely, so I switched on the 10 dB meter attenuation located on the back of the unit. As I pushed the output level up to +6 dB, the 808 started to saturate with some nice, rounded harmonics, giving the drum samples a satisfying gritty vibe with musical character.
Throughout these sessions, the results were a consistent warmth to the midrange, and the low mids occupied a larger region in the stereo field. Upper mids were pushed closer to the listening position, and the center of the stereo image became more dominant. These qualities contributed to the cohesion of the mixes and lend to the description of being “musical.” I printed each of these sessions to compare with the DAW bounces on other systems. The warmth and presence of the API sound, whether through earbuds or a car stereo, always translated nicely outside of the studio environment.
The ASM164 dual stereo bus architecture is ideal for parallel processing, and Todd Humora, Director of Engineering at API, emphasized that it was designed with this particular workflow in mind. You first establish a mix with all of the tracks routed to bus B and a parallel submix with selected tracks on bus A. Next, you insert a stereo compressor on bus A, engage the A to B switch, and use the Output A control to dial in the parallel compression.
I set up a mix of a '70s session with 14 stems. Once the rough mix on bus B was established, five drum tracks were also routed to bus A for the parallel submix. I patched in a pair of API 527 compressors on bus A and selected a fast attack with a 4:1 ratio. As parallel compression was blended with the mix, I trimmed back the drum inputs to find the right balance of levels and threshold settings. As expected, the drums were bigger and more energetic, but interestingly, other parts emerged with a bit more clarity. The parallel compression tamed some of the midrange qualities of the drums and opened up the imaging.
For my next test, I applied parallel compression on a drum and bass session produced in Reason Studios Reason. Once the compressor settings and mix levels were selected, the drum breaks and bass achieved a rich, full sound without becoming overpowering, leaving ample space for the synth and sample parts to spread across the stereo field. After testing parallel compression on other sessions, it became clear that this was indeed the intended purpose of the dual stereo bus design.
The API documentation includes block diagrams of the ASM164 signal path. What caught my attention is that the summing bus can be tapped at the (balanced output) insert Sends before the 2520 op-amp and transformer. For comparison, I ran a session that bypassed the output stage and discovered that the inputs and summing stages, without the output circuitry, sound different. The center of the stereo field is flatter, and elements do not have as much of a forward presence. While there is still some coloration, the overall sound is far more neutral.
James Bernard of Awakened Souls brought over some masters of an upcoming ambient release mixed in Ableton Live [Tape Op #160]. The project was comprised of instruments, vocals, drums, and electronics layered with noise and a lot of reverb wash. Running the masters through the ASM164 pushed the bass and vocal parts forward, which seemed to diminish the stereo image. I then tried something unorthodox by setting up a parallel processing configuration to combine the transformer outputs with the output of the non-transformer insert Sends. With a small amount of the transformer output added, certain percussive elements and transients began to sparkle. The masters maintained the wide stereo image, but transient elements from the API exhibited a dynamic front-to-back activity. The takeaway from this experiment is that the output circuitry of the 2520 op-amp and the transformer account for most of the sonic character; however, the summing bus itself is uncolored. If the need calls for more transparency, the option is there to mix through the insert Sends – the inputs provide enough gain to print a mix without make-up compensation.
Recently, I’ve been working on spatial audio projects, and these productions are centered around a Buchla 200e series modular system, an Eventide H9000 [Tape Op #141], and the Groove Synthesis 3rd Wave Synthesizer [#165] – all running quadraphonic audio. For these projects, mixing in quad occurs within the digital domain, and I’ve been curious to hear how analog summing would compare. After performing some cabling contortions, I had four quadraphonic inputs running through the ASM164, with Output A controlling the front mix levels and Output B controlling the rear channels. It was extremely interesting to hear the API coloration applied to quadraphonic audio. The percussive elements projected more toward the center listening position, and synthesizer drones felt denser with a noticeable midrange warmth. What surprised me was the enhanced projection of the four phantom centers. In the same manner that elements push toward the listener in a stereo mix, this phenomenon was occurring from all directions and created a tighter, more intimate spatial audio experience. It became easier to hear spatial information from almost any listening position. I could sit off to one corner and still hear panning motion articulated clearly from speakers in the distance.
In the spirit of full transparency, it should be known that I have a 500 Series rack with API compressors and API mic pres that see a lot of use. For the purposes of this review, I cabled these to the Insert Send/Returns on the input channels and found it convenient to be able to press a button to have a hardware compressor available on the DAW mix. This is yet another feature that makes the ASM164 so versatile for those of us with hybrid workstation setups. This flexibility could also serve a larger studio situation, and I can see installing one as a dedicated sidecar, with a stereo compressor permanently patched in for parallel compression. As a standalone mixer, it sounds impressive, and for those seeking an analog summing mixer with color, warmth, and musicality, the ASM164 lives up to its reputation of delivering the signature API sound.
($3195 MAP; apiaudio.com)
-Kurt Kurasaki