The ISA 220 Session Pack provides all you need to record your session with precision and Focusrite sonic performance. It features many of the original circuits of the flagship ISA 430 Producer Pack along with some new features of its own. It also features the same digital option as the ISA 430, providing you with a high quality digital route direct from the 220 into your digital recording system.
Precision VU metering of input level or compressor gain reduction (switched)
16 LED Digital Output meters for both internal and external inputs.
Classic Focusrite transformer based Mic pre
Switched High and Low pass filter controls
Switched High and Low shelving filter frequency controls
Optional Stereo A/D – 24 bit 96 KHz Delta Sigma converter running at 128KHz oversampling - dithers down to 20 or 16 bit
Proprietory Focusrite discrete Class A VCA Compressor side chain design for lower distortion and Noise performance
Illuminated push button for switching the compressor between pre and post EQ
New Blend feature for adding dynamics into the compressed signal path
New De-esser design based on optical technology for lower distortion and transparency
'De-esser Listen' for precise control over sibilance
Frequency adaptive limiter to avoid critical digital overs
Overview of the ISA 220
The unit begins with a Precision VU meter which is switchable to allow you to monitor either input level or compressor gain reduction. Situated above the VU meter is a 32 LED digital meter for monitoring from either the internal input or an external input which gives access to the second channel of conversion on the optional high quality stereo A/D card. To the right of the Digital Output meter is a global bypass switch to allow for real A/B comparisons.
Three input options are provided to give compatibility with Mic, Line or Instrument sources. Switching between these input options is available on the front fascia with LED’s indicating the active input. All inputs are transformer based contributing to that all important Focusrite signature sound of clarity without colouration, with incredibly low noise and distortion figures.
The Mic Pre is the classic Focsurite transformer based design as featured in the ISA 110 and Red 1 and 8 (see pages 3, 8 and 9) with illuminated switches for Phantom power and Phase reverse, all immediately available on the Front fascia.
Other switchable controls available on the front fascia include controls and indicators for the Digital option, in/out selectors for each of the sections and a select switch between Mic, Line or Instrument inputs. An instrument jack is immediately available on the front fascia for quick ‘plug and play’ access.
The EQ featured on the 220 is similar in design to the Red 2 and ISA 110 with the exception of the Shelving EQ’s having four positions rather than six. The focusrite EQ is renowned for its musical empathy. For more on the Focusrite EQ, please refer to pages 10 and 11.
Prior to the Compressor section, which utilises the same compressor circuit as the ISA 430, the ISA 220 features a ‘Compressor Pre EQ’ switch. Normally the compressor is featured post the EQ. With this switch you can choose to place the Compressor either pre or post EQ. Also featured in the compressor section, alongside the auto release is the new Blend feature, a unique feature to the ISA 220 allowing smoother compression at more extreme settings. When switched in, ‘Blend’ allows you to mix the uncompressed signal with the compressed, thus retaining a variable level of dynamics from the original source.
Just prior to the Output section, the ISA 220 features the same De-esser as the ISA 430, based on a low distortion optical technology design, letting you transparently remove excessive sibilance from a vocal performance. The circuit uses a combination of threshold dependent EQ and phase cancellation to create a de-esser smoother and less intrusive than traditional compression based designs. You also have the option here, with ‘De-ess listen’ switched in, to monitor the exact frequency you are effecting. Selecting ‘De-ess listen’ inverts the operation of the De-esser and allows the user to monitor only those selected frequencies which will trigger the activation of the De-Esser, rather than hearing the overall effect in a complex signal.
The output section of the ISA 220 features the same frequency adaptive limiter as the ISA 430. The limiter uses three separate stages of Optical based circuits with different limiting properties to give true distortion-free limiting. Fast limiters tend to have problems with complex signals that contain sustained low and mid frequency information and tend to "chop holes" in the audio when HF transients trigger the limiting. The ISA frequency adaptive limiter has three frequency bands with different attack times as follows: LF slow attack, MF quick attack and HF very quick, to catch fast transients. The Limit-in LED illuminates when the limiter is active. An upper threshold is fixed at +20dBu to prevent overload of the internal (or an external) A/D converter.
Finally, a variable control adjusts the module output level between -60dB and +6dB ensuring optimum levels exiting the unit.
The ISA optional A/D converter
The optional A/D card can be factory fitted or purchased later and retro fitted as and when required, to suit your recording budget.
With the addition of the Stereo A/D card the ISA 220 and 430 can be used as high quality mono/stereo tracking converters or at mix down as a stereo converter channel for final mastering.
At the heart of the Stereo A/D card is a high quality 24-bit 96KHz Delta Sigma converter running at 128KHz over-sampling 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 ProTools 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 ISAs have two separate channels available for conversion named the INT and EXT with both fed to the A/D inputs, via the Spectral limiter and high resolution LED meter, giving a clean, protected, high quality path to digital.
INT (Internal Signal)
The internal input to the A/D is normally connected to the internal module channel signal passing through the EQ and Dynamics. However, this point can be broken by the rear INT A/D Direct jack and allows a signal to be directly connected to the A/D input (bypassing the internal processing).
EXT (External Input)
The 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 or for combining signals in Sum mode.
Selectable between 44.1kHz, 48kHz, 88.2kHz and 96kHz.
Bit Rate Select
Selectable between 24, 20 and 16 bits.
Inst. Hi Z I/P: Noise: -96dBu
THD: 0.003% with 0dBu
Mic I/P: Noise: 123dB EIN with 150 ohm input resistance at 60dB of gain
Compressor: Threshold Range: -28dB to +12dB
Ratio: 1.5:1 to 10:1
Slope: Soft knee
Attack: 500mS to 25mS
Release: 100mS to 4S, variable or auto (program dependent)
De-Esser: Threshold Range: 22dB
Frequency Range: 2K2 to 9K2
Ratio at Centre Frequency: 2:1
Limiter: Threshold Range: 20dBu
Ratio: infinite (Brick Wall)
Attack: Frequency dependent
ISA 220 specification compared to the ISA 430:
ISA 430 has: Expander/gate section with sidechain access, sidechain monitoring, external keying, hysteresis. (ISA 220 has no gate or expander)
Insert point which can be post mic pre, pre EQ, post EQ pre-compressor, or post compressor, pre-limiter. (ISA 220 has no insert point.)
Original EQ with 6 frequency selections for shelving EQ (ISA 220 has very similar EQ, but the shelving (hi and lo bands) have only 4 frequency selections (top and bottom frequencies of each band are absent.)
Frequency-conscious compression and gating, (EQ can feed the sidechain of the compressor or gate. ISA 220 has no frequency-conscious compression.)
Split function (ability to use as two separate channels for discrete EQ and compression simultaneously. ISA 220 has no split function.)
Input AND output transformers (ISA 220 has input transformer only. However, note that the ISA 220’s input transformer also applies to the line input, whereas the ISA 430 transformer is for the mic. input only.)
Post mic.pre. output on rear panel (ISA 220 has no separate post mic pre output.)
Instrument input has 10dB more range (0-40dB on the ISA 430, 10dB-40dB on the ISA 220.)
‘Sum’ function in the output section, making it possible to sum the ‘External A/D Direct’ input together with the main internal signal, (ie whatever is connected to the mic, line or instrument input,) from the front panel, routing to the main output. (ISA 220 has no sum function.)
ISA 220 has: "Blend" function in the compressor module. This allows the user to blend compressed signal with uncompressed signal, in the way that many producers do via the faders of an external mixing console. (ISA 430 has no ‘blend’ function.)