Using a Direct Box in your Home Recording Studio

This is a tutorial illustrating the use of direct box in a home recording application. I received an inquiry from a reader about issues on recording a digital piano. Below are the gears and accessories used:

1.) CLP-295GP Yamaha Clavinova digital piano.
2.) Tascam DR-100MKII recorder

Original Recording Path

The reader is actually thinking of recording the digital piano in stereo by using this flow:

Piano > LINE OUT (2 female RCA outputs) > digital recorder > DAW > CD

The recording concept is simple; first connect the piano RCA outputs to a digital recorder line inputs. Final processing (editing, mixing, etc) will need files to be transferred to a computer with DAW software (e.g. Reaper). After completing the DAW session such as mixing and mastering, it can be burned into to a CD.

However, he was thinking about adding a “preamp” before the recorder to increase the quality and fidelity of the sound recording:

Piano > LINE OUT (2 female RCA outputs) > Preamp > digital recorder > DAW > CD

Now he is asking recommendations as to what types and brands of preamps to buy. Do you think a preamp is really needed in this case?

Understanding the Instruments/Gears Inputs and Outputs

The very basic function of the preamp is to take a microphone or instrument level signal input (read more about this topic here) and boost it line levels. It’s important to examine the nature of the outputs and signals involved before you can decide whether a preamp is highly necessary.

One of the important clues can be found in the gear manuals. Example below is the information obtained:

A.) Yamaha Clavinova Digital Piano outputs

Clavinova outputs

Clavinova outputs

There is only one set of analog outputs on this instrument and that is using the AUX out that consists of 2 RCA jacks. These are line, unbalanced outputs. The manual recommends connecting using an RCA to RCA cable from connecting the instrument to a stereo recorder. But this is not the case if you are recording to a digital recorder requiring balanced inputs.

RCA is carrying unbalanced signals and could be susceptible to noise and interference. This is a common source of noise if you are recording using unbalanced outputs. This is not to say that recording unbalanced should be entirely avoided but if you want the capture the cleanest sound as possible from your instrument, you need to record using balanced inputs and audio outputs.

B.) Tascam DR-100MKII recorder inputs

Below are the standard inputs of this digital recorder:

Tascam outputs

Tascam outputs

As usual with any other professional audio equipment, it utilizes XLR balanced inputs that can have two modes:

1.) LINE 1
2.) MIC

According to the manual, LINE 1 is used when you are recording from balanced external audio sources. MIC mode is used when you are connecting a MIC level signal to the digital recorder (not necessarily coming from a microphone).

It is also worth noting that this digital recorder already includes a preamp because it accepts MIC level signals. All professional audio recording interfaces and digital recorders today (as long as they accept microphone XLR balanced inputs) are equipped with a built-in preamp. Therefore, buying an external preamp unit is redundant in this case.

The Recommended Recording Setup – using Direct Box

It is always desirable to have the cleanest sound recording of the musical instrument. One of the gears that could help is using a direct box.

The role of this device is to accept unbalanced RCA/TS line inputs (such as from the digital piano) and then convert this to balanced XLR MIC level (not line level) outputs suitable as an input for professional digital recorder like the Tascam DR-100MKII. The following are the benefits:

1.) Clean recorded signals.
2.) Preserve the original sound of the instrument.
Also using RCA to XLR ready-made adapter cables won’t help because it does not do anything to condition/prepare the signals or matched the impedance to the digital recorder inputs. You really need a direct box to make this conversion correctly and as clean as possible.

In this case, below is the recommended recording setup flow (recording in stereo):

recommended flow

recommended flow

The following are the detailed procedures:

1.) Turn off the digital piano as well as the digital recorder. Do not yet connect the computer to your digital recorder.

2.) Connect the RCA outputs of the digital piano to RCA inputs of the direct box. There are lots of direct box to choose. The important requirement is that it accepts RCA unbalanced connectors as input and provides balanced-XLR outputs. Whirlwind PCDI Direct Box is an example. This is a passive direct box which does not need any external power to operate.

Switch off the pad switch (defaults at O position). You can tweak this later on if necessary.

attenuation pad

attenuation pad