A-D Conversion
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 analog 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 organization of the PCB layout and grounding, ensuring that the S/N ratio and linearity of the converter are optimized. The noise floor and THD (Total Harmonic Distortion) are kept to a minimum by the nature of the power supply and the analog input design, with analog 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 analog units, the signal path is kept as short as possible, having no unnecessary analog 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.

This optional A/D card can be retrofitted as and when required, to suit your recording budget.

With the addition of the stereo A/D card the ISA 430 (and 220) can be used as high quality mono/stereo tracking converters or at mix down as a stereo converter channel for routing complete mixes to digital media.

At the heart of the stereo A/D card is a high quality 24-bit 96 kHz Delta Sigma converter running at 128x oversampling for maximum conversion performance. Focusrite proprietary designs are used for all internal clocking and phase lock loop circuits to guarantee the absolute minimum jitter possible, whether free-running or locked to wordclock or Pro Tools Superclock.

When recording to non-24-bit destinations, 16- and 20- bit dithering can be selected to ensure the highest quality digital conversion for any format. The ISA's optional A/Ds are stereo and allow for input from internal (post-processing) and external sources simultaneously giving a clean, protected, high-quality path to stereo digital media.

INT (Internal Signal)
The internal input to the A/D is normally fed from the internal channel signal passing through the EQ and dynamics. However, this path can be broken by a signal connected to the rear INT A/D Direct jack, which allows a signal to be directly connected to the A/D input (replacing the internal processed signal).

EXT (External Input)
An additional external input (XLR on the rear panel) gives the user access to the second channel of conversion on the A/D card for stereo recording with two units or for an additional external source.