ALLO KALI Reclocker

Canadian company Allo have released an interesting product called the 'KALI Reclocker' that will provide a low jitter I2S input to Raspberry Pi DACs.

The Kali takes the digital audio signals (I2S) from Raspberry Pi through the on board FPGA based FIFO and does the re-clocking of the signal before sending it to the DAC.

So, What Is I2S?

I2S is a communication protocol specifically designed to carry digital audio data. The main advantage over the long establish SPDIF interface is that the I2S interface has a separate word clock. Theoretically, this will allow for lower transmission jitter.

But in theory the Raspberry Pi has a bit of a problem with its I2S output. Since the only clock on board the Raspberry Pi is a 19.2MHz crystal, it should have trouble generating proper clocks for its I2S output. For example, for 44.1KHz audio, the LR Clock must be running at precisely 44.1KHz. That is not possible, since the frequency is not a multiple of 19.2MHz. Thus, the frequency can be either 19.200.000 / 435 = 44.138KHz or 19.200.000 / 436 = 44.0366KHz. This is a limitation of the Broadcom BCM2835 in conjunction with the 19.2MHz crystal and there is nothing that can be done. More detailed explanation can be found on Dimdim's Blog.

Kali the Goddess of Time

Every SBC has a crystal that it used to send digital signals to your DACs.

The accuracy of this crystal is very important in how well the DAC will transform the digital signal into analog sounds. Simply put: a better crystal means a better sound! Most SBCs use a very cheap crystal with lots of jitter in order to save costs.

Furthermore, there are 2 kinds of frequencies for digital files: 44.1Khz (wave files) and 48khz (streamed music). Some SBCs (like RPIs) can output only 48Khz, so imagine the degradation of the sound that was recorded at a different frequency.

Kali will solve both of those problems


NDK clocks
Kali’s output clock is based on a very low jitter Nihon Dempa Kogyo (NDK) crystal, isolated from the world by a low-noise regulator for ultra-quiet power supply.

Re-timing is performed through a Lattice MachXo3 LCMXO3L-4300C PLD / FPGA with 4300 LUTs along with a 4Mbit FIFO RAM which buffers 700ms of audio.

“Since FPGAs introduce about 200ps of jitter, the NDKs re-clock the buffered data outside the FPGA and provide a MCLK/BCLK that is direct from crystal to provide an almost jitter-free clock to your DAC,” claimed Allo.


Features

• The basic design includes FPGA based FIFO board
• I2S input & output: 44.1 KHz, 48 KHz, 88.2 KHz, 96 KHz, 176.4 KHz, 192 KHz ,384 KHz - 16bit, 24bit or 32bit
• FIFO Memory: 4MB SRAM
• LED indicators (Power, Full, Lock, Empty, Sample Rate, Mclk)
• DC power supply: (5V/3A) with Filter circuits
• Multi-frequency output capability to support the full I2S working range from 44.1 KHz to 196 K
• Automatically switching frequencies according to the input I2S signals
• Extremely fast and very low propagation delay Flip-Flops are added on I2s signals
• output from FPGA, for synchronization with MCLK before sending to DAC
• Ultra-low-noise voltage regulators for optimal audio performance
• Integrated EEPROM for automatic configuration (with write-protection)

Tech Specs

• LED indicators (Power, Full, Lock, Empty, Sample Rate, Mclk)
• DC power supply: (5V/3A) with Filter circuits
• Operating Temperature Range is -25C to 85C
• The Kali board size: LWH = 58mm * 77.54mm * 23.8mm

Note: The Kali Reclocker can only be combined with DACs running in Slave Mode, that is it will have to take its BCLK from the RPi and not the other way around. You can use Piano 2.1 - they were designed to work perfectly together!

The million dollar question (actually $75): how does it sound?

Well, the music will "open up". The stage will sound bigger, more tri-dimensional. You will hear sounds, words, instruments that were drowned before in a sea of digital mud. It's like Kali manages to extract more audio content from the same 44.1K/16bit source material. Imagine going from SD TV to HDTV!

To sum things up:

• It’s truly a game changer! The music became more “real”
• Sound improvement is really noticeable: Details and instrumental separation are vastly better
• With the Piano HiFi DAC, it makes a great bang\buck combo!

Support & Downloads

Kali Tech Manual: https://allo.com/documents/sparky/tech-manuals/Kali-Tech-Manual.pdf
Kali I2S Pinout From SBC: https://allo.com/documents/sparky/Kali-I2S-Pinout-From-SBC.pdf
Kali I2S Pinout to DAC Boardshttps://allo.com/documents/sparky/Kali-I2S-Pinout-to-DAC-Boards.pdf


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