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Focusrite ISA 220 Preamplifier/Processor

Holding true to the original vision for Focusrite, the ISA 220 "Session Pack" offers an uncompromised recording channel with a bandwidth of 10 Hz to 150 kHz. The box includes a mic/line preamp, equalizer, compressor, de-esser and limiter.

Holding true to the original vision for Focusrite, the ISA 220 “Session Pack” offers an uncompromised recording channel with a bandwidth of 10 Hz to 150 kHz. The box includes a mic/line preamp, equalizer, compressor, de-esser and limiter. There is also an optional A/D card available (I reviewed the box with the optional A/D). The mic preamp is the classic Focusrite transformer-based design found in the ISA 110, the Red 1 and the Red 8, the EQ is the same as that found in the original ISA 110 and ISA 215 with the exception that the shelving EQ has four positions rather than six and the compressor and de-esser are the same circuits found in the ISA 430. The box’s digital option, also the same as the ISA 430, provides a high-quality digital route direct from the ISA 220 into a digital recording system.
Product PointsApplications: Studio

Key Features: 48V phantom power preamp; compressor; two-band parametric EQ; limiter; de-esser; VU meter

Price: $1,995, optional A/D card, $525

Contact: Focusrite/Digidesign at 650-731-6300, Web Site.

The rear panel of the 9.8-inch deep, 15.4 lbs, 2RU rackmount ISA 220 has a wide variety of connectors that easily adapt to nearly any recording or mixing situation. Two female XLR connectors provide mic and line input and a 1/4-inch TRS jack provides a Hi-Z input. A front panel-mounted 1/4-inch TRS jack also provides a Hi-Z input. A male XLR connector provides signal output.

The microphone and line inputs are transformer balanced with +4 dBu operating levels and a maximum input level of +26 dBu. The instrument input is unbalanced with a -10 dBV operating level and a maximum input level of +10 dBV.

The “Internal A/D Direct Input” 1/4-inch jack is used to route an external signal directly to the A/D card via the limiter. It is fed to the left channel of the A/D card and thus it replaces that channel’s signal feed to the A/D card. This allows another audio path to make use of the ISA 220’s A/D card.

The “External A/D Input” routes an external signal to the A/D card via the limiter. The signal is fed to the right side of the A/D card and does not affect the left channel signal. By using this input, two ISA 220 units can be used to create a stereo recording channel.

The 1/4-inch TRS “Dynamic Link” jack allows two ISA 220 units to be connected with the compressor sections linked to behave as a single stereo unit. The ISA 220 generating the larger control voltage is the controller.

The VU Select switch toggles the VU meter between monitoring input gain and compression. The O/L (overload) LED illuminates when the peak signal level reaches or exceeds +20 dB, or when the peak signal level reaches 6 dB below clipping. The two 16-segment Digital Output Meters monitor the signal after the limiter but before the A/D input.

At the input stage the select button steps through the three input options (mic, line, instrument) . A corresponding LED illuminates to show which option has been selected. When the mic input is selected, the gain range is set from 0 dB to +30 dB, in 10 dB steps or +30 dB to +60 dB, in 10 dB steps if the “30-60” switch is activated. When the line input is selected, the gain range is set from -20 dB to +10 dB in 10 dB steps. When the Instrument Input is selected, gain changes can be made only with the trim control that provides +10 dB to +40 dB of additional gain. When the mic or line input is selected, the trim control provides an additional variable gain of 0 dB to +20 dB.

At the EQ Module, the All EQ switch places the entire EQ module, including the high and low-pass filters, in the audio path. The Filter In switch inserts the high and low-pass filters into the audio path. Both filters provide an 18 dB/octave rolloff. The low-pass filter is variable from 400 Hz to 22 kHz. The high-pass filter is variable from 20 Hz to 1.6 kHz.

The “Param EQ” switch inserts the parametric equalizer into the audio path. There are two separate bands of parametric EQ, each with a continuously variable boost/cut (center detented), a sweep control with two ranges and a variable Q control. The first band is adjustable from 40 Hz to 400 Hz (120 Hz to 12 kHz when X3 is pressed) and the second band is adjustable from 600 Hz to 6 kHz (1.8 kHz to 18 kHz when X3 is pressed).

The Shelving EQ switch inserts the shelving equalizer into the audio path. The high and low-frequency shelving sections each have a continuously variable boost/cut (center detented) and a four position rotary switch that selects the rolloff frequency.

The Comp In switch inserts the compressor into the signal path. The ratio control, which determines the ratio by which the signal is compressed, is variable from 1.5:1 to 10:1. The threshold control, which is variable from -28 dB to +12 dB, determines the level at which the compression begins. The attack control adjusts how quickly compression is applied once the level of the source signal has risen above the threshold and the release control adjusts how quickly the compression is removed once the level of the signal has fallen below the threshold. Pressing the Auto Release switch makes the release time automatic, substituting an adaptive attack/release circuit, which varies the release rate to suit the dynamics of the signal. This enables the use of fast attack times without any “pumping” type artifacts.

The compressor is normally featured post-EQ. Pressing the Comp Pre EQ switch makes the compressor pre-EQ. Also featured in the compressor section is the Blend function. This feature allows smoother compression at more extreme settings. When engaged, Blend allows the uncompressed signal to be combined with the compressed signal. This retains a variable level of dynamics from the original source while still offering control of the dynamics. This operation simulates the practice of mixing compressed and uncompressed signals on two separate channels of a mixing console. The variable Make Up control restores the gain lost due to the signal’s compression.

The de-esser, which is located just prior to the output section, combines threshold dependent EQ and phase cancellation, allowing the user to transparently remove excessive sibilance from a vocal performance. The De-Ess In switch activates the de-esser circuit. The variable threshold control determines how much de-essing is being applied to the selected frequency. The variable frequency control, which is adjustable from 2.2 kHz to 9.2 kHz, selects the frequency to be removed. The de-esser’s active LED illuminates when the de-esser is active at the selected frequency and as the level reduction increases, it shines more brightly.

The Limit In switch activates the multiband limiter. This limiter has three separate fixed frequency bands, each with different limiting properties, to provide low-distortion limiting. The Limit-in LED illuminates when the limiter is active. An upper threshold is fixed at +20 dBu to prevent overload of the internal (or an external) A/D converter. The limiter’s active LED illuminates when the limiter is processing audio. The limiter’s output control adjusts the ISA 220’s output gain between -60 dB and +6 dB.

The digital option, which is user-installed , adds a high quality stereo A/D converter to the 220’s list of features. A high quality 24-bit, 96 kHz delta-sigma converter running at 128 kHz oversampling is the core of the card. Focusrite proprietary designs are used for all internal clocking and phase lock loop circuits guaranteeing the lowest amount of jitter possible.

On the front panel, the Clock Select switches among 44.1 kHz, 48 kHz, 88.2 kHz and 96 kHz. The Bit Rate Select switch chooses 24, 20 or 16 bits. The ext select switch toggles between Ext and Ext/SC. Selecting EXT slaves the ISA 220 to an external word clock source and selecting EXT S/C slaves the ISA 220 to an external Digidesign Superclock source. The Lock LED illuminates to show the unit is locked to an external clock.

The A/D card adds several connectors and switches to the rear panel. Two BNC connectors allow the box to lock to word clock or Pro Tools’ Superclock. Three digital output connectors provide output via AES/EBU, S/PDIF, and/or two-channel optical.

The level switch determines whether a 0 dBFS reading on the meter corresponds to +20 dBu or +24 dBu. The 75 switch terminates the incoming word clock signal with a 75 ohm resistor.

In Use

After opening the ISA 220, I was a bit frustrated when I realized that I was going to have to install the A/D card myself. After popping off the box top, I promptly realized that the installation was a piece of cake and in less than 10 minutes I was ready to rock using both the analog and digital outputs.

The ISA 220 works extremely well with drums and percussion. I had great results using the box along with an AKG D112 on kick drum and with a Shure SM-57 on snare. The box sounded wonderful coupled with a Royer R-122 to record percussion. As an experiment, I tried using the ISA 220 to record kick drum with an SM-57 (the world’s worst kick drum mic) just to see what it could do. I was stunned when I made the kick sound not just good, but great with the 220.

I had fantastic results using the ISA 220 to record vocals with both the BLUE Cactus and the Brauner VM-1KHE. I was extremely pleased with the performance of the de-esser. In comparison to the dbx 902 de-esser (my trusty standard), I found the ISA 220’s de-esser to have substantially fewer audible artifacts.

The Blend function is one of the ISA 220’s strongest features. I found it to work extremely well on bass guitar, electric guitar and excessively dynamic vocals. In every case, I was able to compress the signal more drastically than I normally would while still retaining a dynamic feeling.

I had great results using the ISA 220’s instrument input to record bass guitar. The bass had a nice big bottom end while maintaining its definition and presence. It was no surprise to hear that Simon Osborne (Grammy winner for recording and mixing Sting’s Brand New Day album) has made the ISA 220 his box of choice for recording bass guitar.

I used a Royer R-122 to record electric guitar through the ISA 220 and had wonderful results. The box worked equally well coupled with an Earthworks SR77 to record acoustic guitar.

The ISA 220’s A/D converters sound fantastic. At 96 kHz, I compared their sound to those in my iZ RADAR (my favorite converters) and found the sound to be nearly identical. My only complaint with the ISA 220 is that all of the switches return to their default position after the unit has been powered down but as long as the status of every section is checked after powering the unit up it shouldn’t cause any problems.


In the Focusrite tradition, the ISA 220 sounds fantastic. The box has detail and clarity while remaining clean and quiet. The EQ is powerful yet very musical and the compressor and de-esser are quick and easy to use; they sound extraordinary. Likewise, the blend feature and the multiband limiter are the icing on the cake.