For this week’s EYE ON NPI we’re going to put a bug in your ear, with the Knowles IA611 SmartMic Audio Processor (Short Link) – perfect for making intelligent headsets, earpods or other low-power microphone devices. We’ve covered plenty of microphones before, including MEMS mics, and they’ve always been pretty straight forward: audio waves are detected, converted to a voltage, then piped out over PDM, I2S or analog. This microphone is particularly nifty, it can output I2S or PDM but it also has a built-in DSP processor that can detect keywords even in ultra-low sleep modes. This chip is specifically designed for making smart earpods, but would do well in any battery-powered product that needs voice activation
Voice-control is nifty and is becoming a standard for home automation, phone or headset control. (Virtual Assistant) Voice control has no fiddly buttons, is firmware-adaptable, and of course its hands-free so folks can use even when the device is not nearby, when occupied by other tasks, or in need of accessibility technology (Link).
The down side is that humans have this nasty side effect of speaking whenever they feel like it, not just after pressing a button or emitting a unique frequency tone. So, getting the device’s attention is a big engineering challenge. On one hand (ear?), you want your device to be really responsive, so you have to constantly be listening and analyzing all audio. On the other hand, listening and processing audio is very power consumptive, and unlike BLE you can’t just wake up every 20 ms to see if there’s a preamble, or request the person to repeat the command constantly (Link) – you really do have to listen all the time.
Now, if you have a ton of budget, and the ability to design custom silicon, you can of course design your own chipset, specifically for low power ‘on the edge’ audio detection (Link). But, chances are you don’t have that massive budget. Instead, you can use the Knowles IA611 (Link) – a microphone that does all the low-power DSP work for ya, and can be programmed with custom wake words for your product. You’ll still need to collect a lot of voice data to make sure you cover various accents and pronunciations, but at least you skip over all the gnarly DSP and co-processor work.
The IA611 is the same size as your everyday I2S/PDM mic but has many more pads. These can be muxed to be I2C, UART or SPI controlled so just about any processor can interface with the DSP inside. For audio, you can have I2S or PDM, again very flexible! The data port is used to download firmware/voice models to the DSP, which is done at boot. Inside, the microphone element is in an ultra-low power sleep mode, waiting for audio level to be detected. Once there is some audio, it wakes up into a low power mode, enough to listen for and detect the wake word. When the wake word is detected, an interrupt is triggered on the host processor, and the sensro starts recording audio into an internal buffer. That way, when the host is fully awake, it can read the last 3 seconds of audio and process the command at full power. The mic then transitions to a pass through mode, basically a normal I2S or PDM mic, while the powerful host processor analyzes the more complex commands.
All together this is an impressive feat of engineering ‘slight of hand’ – the wake word detection is done only at the ultra-edge, and then slips out right as the command turns into a complex natural-language-processing event. We think this could be great for products that need to add low-power voice communications and need to do it fast. Knowles provides an SDK (Link) and a training app, you can then use that to generate voice models that are uploaded as binary files to the DSP chip via the example software that runs on a SAMD21 eval board (Link).
Both the AI611 eval board (Link) and bare AI611 SmartMic audio processors are available and in stock at Digi-Key right now! If your product has wake-word control in the design specifications and you want to save yourself 6 months of development heartache, the SPK2611HM7H (Link) is the perfect fit at a great price. Order some today and you can design it into your product by tomorrow evening.