The ISA stereo ADC embodies cutting-edge conversion technology, encompassed within pristine Focusrite circuitry, providing 2 channels of the highest quality 24-bit conversion at all sample rates up to 192kHz. Digital output formats include 2 channel single/dual wire AES/EBU or 2 channel S/PDIF, all via a 9 pin D-type connector, as well as optical S/PDIF and ADAT. The ADAT (TOSlink) port is stereo and operates at 24-bit, up to 96kHz.
The card can be retrofitted to an ISA 430 MKII or an ISA One at any time.
Just paying for the PCB and circuitry, without any additional casing and metalwork, affords a considerable reduction in cost whilst maintaining an extremely high level of sonic clarity. However, the benefits from installing Focusrite’s optional ADC extend far beyond the obvious financial advantages and space saving issues. As most converters use the same chips, it is the quality of the surrounding analogue circuitry that makes the difference. This is the reason why the ISA ADC is unrivalled in terms of both price and performance.
Focusrite’s R and D team have carefully considered the organisation of the PCB layout and grounding, ensuring that the S/N ratio and linearity of the converter are optimised. The noise floor and THD (Total Harmonic Distortion) are kept to a minimum by the nature of the power supply and the analogue input design, with analogue filtering positively effecting the sound of the digital noise.
In addition, the supporting circuitry around the ADC (dealing with data transmission, bit reduction and incoming word clock) has been carefully structured, as it influences the converter through heat, power supply and data jitter. One of the most important aspects of the ADC is the clock design, as this determines the linearity of the digital output. All Focusrite ADCs are designed to have incredibly low jitter figures (44.1kHz-192kHz < 20 psec) which significantly improve the quality of the sound.
With the converters housed within the analogue units, the signal path is kept as short as possible, having no unnecessary analogue connections to the inputs of recording equipment. In addition, Focusrite units do not contain extraneous clocks or other sources of digital noise, unlike so many digital desks and multi-I/O DSP configurations.