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Under The Hood: Semiconductors In Audio

Semiconductors are essential building blocks of most modern electronics, with the progression from discrete transistors to integrated circuits largely universal, chips dominating usage.

Semiconductors are essential building blocks of most modern electronics, with the progression from discrete transistors to integrated circuits largely universal, chips dominating usage. Participating in a Pro Sound News year’s survey on trends in semiconductor application were Great River Electronics project engineer Dan Kennedy; senior design engineer at Apogee Digital, Lucas van der Mee; B.J. Buchalter, VP R&D at Metric Halo; Crane Song president Dave Hill, and from Lynx Studio Technology, co-founder and chief hardware engineer Bob Bauman.

Four of our virtual panelists agree that ICs they have traditionally used are harder to source, with van der Mee calling it “a common problem nowadays… some of our older products, we cannot repair,” he shares, “simply because parts are not available anymore.” Only Bauman says his company was not having such problems, adding “I hope it continues this way!”

Apogee’s Symphony I/O is an example of a product package made possible by the use of surface mount components. Great River has addressed the problem in advance with lifetime buys of critical chips, says Kennedy, while Buchalter says Metric Halo primarily redesigns circuits as needed. It’s a mix of the two approaches for Hill. “With new designs,” says van der Mee, “we always check with manufacturers about the life of a part. It can be even as simple as asking which footprint will have the longest life.”

The use of surface mount components either completely dominates modern circuit design, or is on the rise, for Hill and Kennedy. These tiny, robotically placed parts don’t have the ‘legs’ of chips of old and are closer to the size needed by the circuitry internal to the chip rather than the size being dictated by the traditional packaging and the need for leads that can extend through printed circuit board holes. SMD parts, allowing for far greater circuit board densities and thus, smaller size, have all but replaced through-hole design chips.

Our respondents largely do not fall back on favored legacy ICs. “[Obsolescense] is way too risky and new parts are simply too good to ignore,” offers van der Mee.

Integrated circuits do not operate in isolation. Discrete semiconductors—transistors and diodes—and components like capacitors and resistors are necessary in electronic designs. Kennedy reports that film caps and FETs” are tougher to find.” Hill adds conventional transistors to the “big problem” list, saying that “some thru-hole transistors are no longer made and there are no SMD versions.” van der Mee also laments the rapidly declining availability of transistors and jFETs, “I guess as a result of the shrinking market. It is a shame, as I still like to do some discrete design here and there.”

Our respondents have migrated to new opamps (operational amplifiers, standard building blocks in audio circuits) over the years, with TI/National components getting all the specific kudos. New demands for portable and battery/USB powered devices puts new demands on components. Buchalter speaks for most of the interviewees when he says he has found “newer opamps that provide exceptional performance with very low power requirements.” Analog component improvements have come primarily “in performance vs. price and power,” says Buchalter, which “allows for denser designs.” van der Mee offers fully differential opamps and analog switches as two areas where he’s seeing improvements in analog components, elaborating that for the latter, “the advantage is cost and size. It allowed me, for instance, to design the insert routing matrix for the Symphony IO preamp. It has 256 analog switches (and 64 opamps) on a circuit roughly the size of a playing card.”

Mic pre switchers are the only modular analog parts (dynamics engines, balanced drivers and receivers, VCAs and other circuits built into a single chip with minimal external components) that van der Mee says he employs. “THAT’s 5171 is at the heart of most of my mic pre design gain switching,” he elaborates. “It is a great part as it allows for your own implementation/configuration.” The THAT 5171 “allows digital gain control of an analog signal and it works well,” echoes Hill.

Kennedy also looks to THAT for line receivers and drivers (balanced input and output circuits on a chip), and also uses “PGAs [Programmable Gain Amplifiers] from TI. Otherwise, generally, dual opamps and CMOS switches make up the bulk of the ICs in our audio products.” Bauman says that Lynx uses “a mix of balanced receivers and discrete designs for analog inputs.” The receivers are used “in cases where space is an issue.”

Digital semiconductor devices include converters and DSP components. The launch of new professional quality components has slowed, with research no longer focusing on improving the quality of digital conversion devices as much as on low power operation. Despite that, van der Mee notes that “there are still interesting developments. It is nice to see AKM work very hard to get true high-end chips in the market. ESS is of course another powerhouse for high-end conversion. We were the first to use their DACs in the pro audio market.” Hill is seeing some interesting components being introduced; Bauman agrees, noting that “AKM apparently has some new devices coming to market that look promising on paper.”

Hill calls out AKM’s AK4490 specifically as a DAC chip with “better filters and linearity.” Cirrus Logic parts had “been my choice for a decade,” says van der Mee, but adds that Cirrus “seemed to have lost interest in our side of the market.” He says he’s employed an AKM chip into an ADC for the first time—the AKM AK5388, a “good, affordable, solid performer.” He adds that chip maker ESS “pulled it off again” with its ES-9018K2M Reference DAC, describing the DSD/PCM, 2-channel DAC with integral volume control as “even smaller and even more efficient, giving unrivaled performance. The chips are great-sounding.”

For getting digital audio in and out of devices ranging from DAWs to loudspeakers, a broad array of interface standards are deployed. Crane Song is sticking with AES3 and ADAT optical for now, while Lynx has added a Thunderbolt card to its converter options.

At Metric Halo, a FireWire pioneer, Buchalter says that USB, Thunderbolt, MADI and Ethernet are in use. On Ethernet, he says, “we have implemented MHLink—which is an exceptionally low-latency (1 sample), high-bandwidth (128 channels/direction/port @ 192 kHz) point-to-point link over GigE. Our use of GigE is soft, however, so we have left open the possibility of implementing one or more of the more generic networking protocols (Ethernet AVB, AES67, Dante).”

For Apogee, Thunderbolt and USB are the interfaces of choice, being “universal and standardized,” says van der Mee. “Ethernet has our attention,” he continues,” but we haven’t included it yet for the lack of a true universal standard for audio (and video) application.” While these manufacturers are largely satisfied with the current crop of interface devices, Buchalter says Metric Halo transitioned to digital I/O implemented in FPGA logic (Field Programmable Gate Arrays, flexible devices that can be programmed to perform a broad swath of audio applications), noting, “We have found that the current interface devices are either too expensive, too limited or have obsolescence problems, and have decided to decouple ourselves from those issues.”

Our panel is keeping tabs on movement towards interoperability between Ethernet audio standards (OCA and AES67), save for Hill who explains that “all the new formats are a large task for a one-person operation and that is before you need to deal with drivers for PC and Mac that change each time they change the OS.”

Given a chance to comment on topics covered or questions not asked, Bauman notes that at Lynx, “Most of our products are based on FPGAs. We can do lots of stuff in one chip and can continue to add features in the field via firmware updates.”

The final word goes to van der Mee: “The even further miniaturization of parts is great, but also a challenging development…It is wonderful as you can put so much circuitry on small footprint, but for debugging, it is a nightmare.

“The number of new power management parts is astounding…As a result, our units have very elaborate power designs—which is very important. As I like to say: Ask an athlete about their secret? The food they eat will always be part of their answer.”