The Channel Strip Audio API

The API Audio The Channel Strip is one of the most complete and high-performance preamplifier modules In addition to integrating the 512C preamplifier , the set also includes various other additional modules. This is the case with the famous 527 multi-mode compressor , the legendary 550A equalizer and the essential 325 Line-Driver .

The Channel Strip Audio API provides a wide range of advanced settings that can be configured in various modes. Does its purchase represent a good investment for a vocal processing and recording in professional studios? Below is our review and complete test on The Channel Strip Audio API!

API Audio The Channel Strip Preamp Overview

The API Audio The Channel Strip is a complete preamplifier with microphone input that allows dynamic sound processing . Like a Core, it brings together several modules ( preamp, compressor, audio equalizer and Line-Driver) in a single assembly.

Its equalizer provides high-precision sound purification as well as optimal output level control for a listening experience that is both rich and immersive .

Equipped with a wide signal meter , several balanced input points and an output mute switch Much like the features of an SPL Goldmike 9844 preamp , its channel strip provides all the essential multi-channel preamp functionality.

The Channel Strip Audio API can also fit in a rack. Which makes it practical to use as an amplification stage with a mixing desk or any other sound processing console . Its choice remains ideal for anyone looking for a multichannel amp .

The result of an ingenious and careful design, the API Audio The Channel Strip preamp is equipped with all the functions necessary to optimal mixing and sound recording quality

First, it consists of a 512C preamplifier which combines the advantage of integrating an input for a studio microphone and a line input which itself remains switchable to serve as an instrument input. We then find a multi-mode compressor 527 which has a fully adjustable threshold, and various notched adjustment potentiometers: Control Attack, Release and Ratio.

The API Audio The Channel Strip is also equipped with a 550A equalization panel specific to this multi-channel preamplifier. This dedicated EQ setting has three frequency bands (Bass, Mid and Treble) all switchable (separately) and provides up to 12 bB of boost or sound cleansing.

The integrated “BP ​​Filter” switch allows you to filter the bandwidth from 50 Hertz to 15 kHz . Upon its release, the API Audio The Channel Strip preamplifier unit is also equipped with the famous 325 Line-Driver . A patented and completely proprietary design, which sets it apart from other drivers. It includes a level potentiometer output a 10-level VU meter .

The Channel Strip Audio API meter itself is switchable and allows you to monitor the preamp output level . Each preset and sound pre-processing element of the preamp can be configured and controlled individually.

A toggle switch allows the compressor to be routed internally after the EQ. The API Audio The Channel Strip also provides additional functionality including a Side-Chain input and an API 2520/Transformer combination .

The Channel Strip API includes:

• The API 512C preamplifier
• The API 527 compressor
• The API 550A equalizer
• The API 325 line driver
• Internal routing that supports multiple configurations,
• A complete audio interface with several rear panel insertion points,
• Two VU meters with RGB LED display and comprising 10 segments,
• Output clips at +30 dBm,
• A fully discrete signal path from the API,
• Transformer outputs.

The preamp features of The Channel Strip API

The 512C preamp from API Audio The Channel Strip is equipped with a microphone input which is compatible with any type of microphone (a ribbon microphone , a dynamic microphone and a condenser microphone), an instrument input, and a line preamplifier . Everything has been designed and thought out to provide dynamic and pleasant front-end sound whatever the types and needs of recordings.

very high-fidelity sound quality with maximum noise reduction . The manufacturing of the 512C preamp integrated into the API Audio The Channel Strip remains entirely faithful to the design circuit typical of all models of amps and preamps from API.

Equipped with all the preset functions essential for audio recording , The Channel Strip Audio API preserves the sound imprint characterizing this brand's Hi-Fi sound equipment. Its wide variety of analog inputs and its various input access points make this Core a preferred preamplifier in the recording studio. The API Audio The Channel Strip amplifier module features:

• A microphone preamp offering 68 dB of gain
• Unity gain line preamp
• An instrument preamp with 50 dB of gain
• A line attenuator
• A microphone attenuator
• Switchable 48V phantom power
• A polarity reverser
• An output peak indicator
• An LED VU meter to monitor output level
• XLR MIC input on the rear of the module
• Instrument input (INST) on the front of the module
• A line input on the back of the module
• A line output on the rear preamplifier module

The Channel Strip Audio API: Input section

The API Audio The Channel Strip's 512C preamplifier module receives three input sources. On the rear panel, there is a MIC input for an XLR microphone ( like a ribbon microphone ) with switchable 48 V phantom power.

Apparently, this preamplifier is not compatible with dynamic microphones with USB input. If you plan to use a Rode Podcaster USB dynamic microphone , you must use a USB audio adapter while taking care to deactivate the 48V phantom power .

Likewise, The Channel Strip Audio API can be used to pre-amplify , compress and process the audio signal coming from various other sources: PlayStation console, Blu-Ray player, turntable, Macbook, PC for Game Engine, Laptop, television connected to UHD display…

To do this, you will need to use a converter , a connector switch or specific DSP type processors.

If you plan to use it to amplify sound emanating from a computer, it will be better to find compatible apps or configure the preamp with audio processing software . For sound processing from Mac or any other type of Apple device, it is recommended to use the Logic pro app or Logic Audio software compatible with your Mac.

For streaming soundtracks , the ideal would be to install one or more Plugins. We must also ensure that the Plug-in in question is risk-free, even if it means using an SSL protocol to guarantee that the preamp is not infected.

Installing a Plugin may also prove useful depending on the connected terminal that you wish to connect to The Channel Strip Audio API via digital port. We can also use Flutter to optimize the automation of certain repetitive tasks under the control of a specific interface developed using this specific open source tool from Google. You will be able to structure your data in the form of an array for greater ease of access.

Still on the rear panel, you can directly connect a LINE input for VST (i.e. virtual) instruments balanced TRS line level . The front panel, for its part, receives an INST input on a 6.35 cm analog jack and which will serve as an unbalanced instrument level input.

The mic input provides 48 volts of phantom power to the MIC IN female XLR connector and is specifically dedicated to condenser microphones . This female XLR microphone input with 48 V phantom power works with a -20 dB attenuator . The corresponding input switch lights blue when functional.

The peak indicator lights purple when the output signal exceeds +27 dBu . This preamplifier module allows you to insert a -20 dB attenuator after the microphone input. The corresponding LED lights up when the PAD is engaged.

The module's GAIN function allows you to control the microphone preamplification level in three adjustment modes: nominal gain of 34 dB , maximum gain of 68 dB , minimum gain of 14 dB when the -20 dB is activated.

The instrument input is activated when the INPUT switch is pressed until it lights up. In this case, the INST 1/4" jack input jack accessible from the front panel will serve as the active input. This instrument level input is a high impedance unbalanced input. The corresponding INPUT switch lights yellow when activated.

The peak indicator illuminates orange when the output sound signal exceeds +27 dBu . The INST input also has a GAIN function to control the instrument sound preamp gain level at the output. The minimum threshold is 14 dB and this gain can be increased up to 50 dB .

Line level input can be activated by switching on the INPUT switch. Note that the corresponding INPUT switch should not light up when active. In this configuration, the 6.35 cm LINE IN jack on the rear of the preamp module will serve as the active input. Its peak indicator illuminates red when the output signal level exceeds +27 dBu .

The corresponding PAD allows the insertion of a -6 dB after the line input. Its display LED lights up when activated. There is also a polarity inverter (or phase inverter) available at the output of the 512C preamplifier. Likewise, the corresponding LED lights up when the phase inverter is active.

The audio signal level coming out of the preamp can also be controlled in two ways using a specific level meter On the one hand, we can access a level meter which gives a direct visual overview of the output level of the preamp . On the other hand, we can also use the peak indicator .

The Channel Strip Audio API: extensive configuration possibilities

The POST EQ switch, once activated, will have the effect of shifting the 527 compressor after the 550A equalizer of the API Audio The Channel Strip preamp module. When the POST EQ switch is engaged, the signal flow will follow its normal path, i.e. left to right.

This will therefore first be amplified in the preamp 512C before its compression in the compressor 527. Then, the signal will pass through the equalization circuit of the equalizer 550A and will pass through the INSERT before its output.

Activating the COMP BYPASS switch , on the other hand, will have the effect of shortening the signal path by completely dispensing with the 527 compressor. This in particular thanks to a hardware bypass based on relays .

Regardless of the signal flow order in which the position of compressor 527 is assigned, it will be completely bypassed. The signal flow still starts from the 512C preamp and will pass through the 550A EQ, but it will go directly to the Insert before output without passing through the 527 compressor.

As with the 527 Compressor, passing through the 550A Equalizer's EQ circuit can be eliminated by activating the EQ BYPASS switch . The signal flow will start from the 512C preamp and go directly to the 527 compressor, without passing through the 550A equalizer.

The signal can then continue its path in Insert before its output. As for the INSERT switch, activating it will route the signal to the API 325 Line-Driver input.

From the rear panel of The Channel Strip Audio API, the signal path will take place in reverse order, therefore from right to left. The configuration of the two interfaces (front and rear) remains constant, for better workflow regardless of the order in which we classify the compressor 527 and the equalizer 550 for audio signal processing .

This will always start from the rear 512C preamp, pass through FIRST EFFECT and SECOND EFFECT before continuing through INSERT and out through the speakers. Note that the PRE OUT , FIRST EFFECT OUT and SECOND EFFECT OUT are all separation outputs.

This means that their connection to the input and to which they are standardized will not be affected when a plug is inserted. The FIRST EFFECT IN and SECOND EFFECT IN jacks are all switching jacks . This means that the connection with the output to which they are standardized will break as soon as a plug is inserted.

The input power supply is carried out using the signal present on the inserted plug. Note for the case of INSERT RETURN that it can only be operational after activating the INSERT switch on the front panel.

The Channel Strip Audio API: The Back Panel Interface

From its rear interface, The Channel Strip Audio API offers a complete package of functions and configurable options . All audio inputs and outputs are balanced except for the mic and instrument inputs. The channel strip provides multiple audio inputs at different points in the audio path.

First, we find the MIC IN input which acts as a microphone input to the 512C preamp of the API Audio The Channel Strip. This balanced, low-impedance XLR female input accommodates XLR-type and condenser microphones such as the Blue Spark SL, Audio-Technica AT2020, or the AKG C414 XLS, etc.

The LINE IN input, therefore line level , accessible from the rear panel, is also balanced. For the INSERT RETURN input, the signal present there can replace the input of the 325 Line-Driver, once the INSERT switch is activated.

Note also that the channel strip of the Audio API The Channel Strip provides several audio outputs at different routing points of the audio signal. All outputs are non-switchable so as not to interrupt their connection with each powered input. At the end of the MIC IN, on the rear panel, we find the CHANNEL OUT output which will serve as the line level output of the 325 Line-Driver.

The PRE OUT output which is located just after the LINE IN is a “ semi-normalized ” output which is used to power the FIRST EFFECT IN . The FIRST EFFECT IN input thus supplies the first processor in the audio path (which should normally be compressor 527). As for the FIRST EFFECT OUT output, it is “semi-normalized” to be used to feed the SECOND EFFECT IN output .

For the SECOND EFFECT IN input, it feeds the second processor in the audio routing, which in turn should normally be the 550A equalizer. For the SECOND EFFECT OUT output, it is “semi-normalized” to serve as a power supply to the input of the 325 Line-Driver . The PRE OUT, FIRST EFFECT OUT, and SECOND EFFECT OUT jacks all serve as splitter outputs .

This means that the connection to their input in order to standardize the sound signal cannot be interrupted when a plug has to be connected. Conversely, the FIRST EFFECT IN and SECOND EFFECT IN jacks serve as switching jacks. This means that their output and normalization connection is interrupted when a plug is inserted. In this case, input power should normally be supplied via the signal present on the inserted plug .

The INSERT RETURN plug, for its part, remains inactive as long as the INSERT switch accessible from the front panel is deactivated. As soon as the Insert switch is activated, the INSERT RETURN input will replace that of the 325 Line-Driver.

The 527 compressor provides two modes of external control: either from the SIDE CHAIN ​​input, or from via the DC link. SIDE CHAIN ​​input is none other than the detector path which integrates the THRUST® filter and the RMS detector .

When a compressor type setting is set to NEW , the side chain is fed from a signal input split of the 527 compressor. When this option is enabled, the side chain signal can be alternately fed starting from the signal introduced to the COMPRESSOR SIDE CHAIN ​​IN on the rear of The Channel Strip Audio API.

The Channel Strip Audio API 527 compressor can also be connected to other 527 compressor units for stereo audio recording and for multi-channel applications. As for the DC LINK, it serves as the control voltage input and output jack for the 527 compressor.

The API Audio The Channel Strip can be powered at 115 volts or 230 volts ( 50-60 Hz ). Power is supplied from the IEC connector on the rear panel. You can easily choose the operating voltage using the voltage selector of The Channel Strip Audio API.

This API Audio The Channel Strip power switch is located at the bottom right corner of the "API The Channel Strip" logo on the front panel. A blue LED will illuminate to indicate that the device is powered and functional .

In addition, you can also discover our test guide and review of the Shure Super 55 Deluxe . This guide presents the sound quality, frequency, technical characteristics, as well as our opinion on this dynamic microphone.

Focus on the sound quality of the API Audio The Channel Strip preamp

The Channel Strip Audio API a set of modules consisting of preamp, compressor, equalizer and line driver. Well beyond its primary role of preamplifying and compressing the incoming audio signal, The Channel Strip Audio API also provides a complete range of equalization options via its 550A equalizer.

Designed by the legendary Saul Walker in the 1960s, the current EQ that powers the API Audio The Channel Strip initially served as a modular OEM EQ . Sixty years later, the 550A equalizer remains a reference and stands out from other equalizers integrated into sophisticated and modern amplifiers.

For several decades, the same type and model of equalizer played a large role in the recording industry . The 550A equalizer is ideal for mixing and balancing sound using appropriate monitor headphones. 21-point reciprocal EQ and 7 boost steps up to a maximum of 12dB of gain or cut at each point.

Its equalization points are divided into three overlapping ranges. The high frequency ranges, like those in the low frequencies, are selectable separately as peak or plateau . We can even add a bandwidth filter , independently of any other equalization settings made in monitoring on this slice.

The 550A equalizer provides three bands of equalization and a band-pass filter . The IN function allows you to activate or deactivate the internal equalizer bypass. CENTER FREQUENCY knob provides 7 center frequencies indicated in blue numbers. The BOOST/CUT (Ring) potentiometer allows you to adjust the signal and purify it to plus or minus 12dB .

The HIGH SHELVING is a high frequency band clipping switch. The LOW SHELVING is used to switch the clipping of the low frequency band . The BP Filter filters the bandwidth in Input and Output. The POST EQ setting switches the 527 Compressor after the 550A EQ in the audio signal path.

The Equalizer Bypass or EQ BYPASS completely removes the 550A EQ from the signal flow. The Channel Strip Audio API 550A EQ also features a center frequency knob of 30 Hz , 40 Hz , 50 Hz , 100 Hz , 200 Hz , 300 Hz and 400 Hz .

All frequencies below the selected center frequency can be boosted or cut. The mid-frequency band allows you to set the sound at 200 Hz , 400 Hz , 600 Hz , 800 Hz , 1.5 kHz , 3 kHz and 5 kHz .

The high frequency band, for its part, locates the sound signal at 2.5 kHz , 5 kHz , 7 kHz , 10 kHz , 12.5 kHz , 15kHz and 20kHz . dB @ 50 Hertz to 15 kHz bandwidth filter can be inserted into the 550A equalizer circuit by activating the BP Filter switch.

Routing of the Channel Strip Audio API 550A EQ can be done by choosing from three options. For post-compressor mode , the 550A equalizer is placed after the compressor and is located before the output section.

In pre-compressor mode , the equalizer is placed after the preamp and just before the compressor. In Hard Bypassed mode , the 550A equalizer can be permanently removed from the audio signal path.

In the default signal flow, no routing switch is activated, the 550A equalizer receives the signal output from the 527 compressor. The Sound EQ of the Audio API The Channel Strip can also be removed from the path of audio signal by choosing between the EQ BYPASS option (to bypass it) and the IN switch.

In the output section of the 325 Line-Driver, there is a CUT button which is used to cut the main audio output. This mute control function can also be controlled remotely via the EXT key . The Channel Strip Audio API is equipped with an HDMI port for the switcher (CUT).

The technical characteristics of The Channel Strip Audio API

512C Preamplifier Specifications:

• Rear connector: XLR microphone input
• Balanced 1/4” TRS LINE input
• Front connector: unbalanced instrument input
• MIC gain range: 14dB minimum, 68dB maximum
• INST gain range: 14dB minimum, 50dB maximum
• Maximum input level: MIC: +8dBu
• INST maximum input level: +36dBu
• MIC input impedance: 1,500 Ohms (microphone 150 Ohms )
• INST input impedance: 20,000 Ohms
• Clipping level: +30dBu
• MIC equivalent input noise: -129 dBm
• Output peak indication: +27dBu
• Actual measured noise MIC: -95 dBm
• Frequency response: +0 , -3 , 30 Hz to 20kHz
• INST equivalent input noise: -125dBm
• Distortion: less than 0.05% +4 dBu output ; less than 0.1% at output +28 dBu
• Actual measured noise INST: -90dBm

527 Compressor Specifications:

• Attack time: 1 millisecond to 25 milliseconds
• Release time: 0.3 seconds to 3 seconds
• Threshold controller range: +10 dBu to -20 dBu
• Frequency response: +/- 1dB 20 Hz to 20kHz
• Total harmonic distortion: < 0.2% THD , any level below clipping, any compression setting
• Measurement: 10-segment red LED: gain reduction scale; -1.5 dB to -23 dB

550A Equalizer Specifications:

• Insertion loss: none
• Frequency response: ±0.5 dB from 30 Hz to 20 kHz
• Noise: Unrivaled output noise of -90 dBm high level hoop, –98dBm low level hoop
• Frequency range: 20 Hz to 20 kHz unweighted
• Distortion: 0.05% THD max , 30 Hz to 20 kHz at +4 dBm , 0.07% THD max , 30 Hz to 20kHz, +18dBm

Line-Driver 325 specifications:

• Output fader control gain: -∞ to +10dB
• Clipping level: +30dBu
• Channel output: +4 dBu , balanced, low impedance, XLR male
• Output impedance: less than 75 ohms , balanced transformer
• Measurement: 10-segment red LED: VU scale ( -20VU to +3VU )
• Switchable between 512C Preamp and 325 Line-Driver outputs

Our opinion on the API Audio The Channel Strip preamp

The API Audio The Channel Strip is the ideal choice of preamplifier and PA equipment for anyone who wants to produce a professional quality sound recording. Given that we are dealing here with a sophisticated all-in-one multichannel preamplifier, its handling requires good skills in sound engineering, sound mastering or sound hardware.

If this is your case, you can without hesitation opt to purchase this fabulous Audio Channel Strip preamplifier from the API brand. Otherwise, you must follow a specific tutorial series. As an alternative, you can always choose a tube preamplifier.

However, this type of preamp remains fragile despite its very easy handling compared to The Channel Strip Audio API. The advantage with this API multichannel preamp lies above all in the fact that its purchase saves you from having to replace the tubes since the API Audio The Channel Strip does not include replaceable tubes.

Its use allows you to purify, optimize and personalize the sound exactly the way you want to hear it. Due to its great versatility, The Channel Strip Audio API also remains ideal whether for sound mixing of samples and tracks, audio mastering or audio enrichment of video tracks.

Likewise, for the digital audio twin (or digital audio replica) and for the exclusive digital content available in the Deluxe edition. The Channel Strip Audio API could also prove useful in a media broadcast studio or in a large production house (almost) as notorious as Universal Studios.

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