Direct Instrument Recording
Although the USB audio interfaces described in Selecting an External Microphone can be very pricey, even the most basic of models offer the ability to record your compatible instrument directly. Whether you are a teacher or student, the ability to directly capture your instrument's sound for online lessons adds immensely to the quality of your lessons. With the right software (normally included with audio interfaces), you can also record and compose your own music.
Compatibility
In order to determine if you can record your instrument directly, you first have to check if your audio interface has a second input available. In the example model below (3rd generation Focusrite Scarlett Solo), we have two inputs available.
The first input (labelled 1) is a dedicated microphone input and uses an industry standard 3-pin XLR jack. The second input (labelled 2) is available for instrument use, and uses a 1/4" jack that is common with guitar cables, DJ/recording equipment, and studio headphones.
High and Low Impedance
An important thing to note on many audio interfaces is the presence of an Instrument or Hi-Z switch or button. In the interface model shown above, the instrument button is used when you are plugging in a High Impedance sound source. You should disable this when using a Low Impedance or Line-Level sound source. If you are unsure what this means, follow the general guidelines below:
High Impedance: Electric guitars with passive pickups (direct without amp), some guitar effect pedals, electric pickups for other instruments such as violins, karaoke microphones
Low Impedance/Line-Level: Headphone outputs from tablets/computers/smartphones, headphone outputs from digital pianos/keyboards/guitar amps, Line Out or Aux Out outputs from high end guitar amps, most guitar effect pedals, guitar Preamps (active pickups and most acoustic-electric guitars) and multi-FX units, Line Out outputs from computers (blue speaker jack)
It is important to properly match your device impedance with your audio interface setting. Using the incorrect setting can lead to either low sound levels or distortion (and potential damage to your interface). Some interfaces, such as the Steinberg UR22, label High Impedance as Hi-Z. Turning or switching on Hi-Z prepares the interface for high impedance sources mentioned above. If you’re are unsure, consult your audio interface's user manual.
NEVER CONNECT the Speaker Out of any guitar amplifier to the input of your interface or you will damage the unit!
Connectivity
Assuming you have an instrument with some type of standard output, all you need to connect your instrument to your audio interface is an appropriate cable. If you are using an electric guitar/violin without an amp, you can simply connect the guitar into your interface (like if your interface was the amp itself) and ensure that Instrument/High Impedance or Hi-Z is turned on. If High Impedance or Hi-Z is turned off, you will get little to no volume, even with the Gain knob set to max.
For other instruments, use the line out or headphone out and the Low Impedance setting on our audio interface (Instrument or Hi-Z turned off). Below is an example of the rear I/O panel of a Yamaha P-115 digital piano.
The Aux Out (line out) has two options: separate left and right jacks, or a combined stereo jack built into the left output jack. We should note that the instrument input on an audio interface is normally a mono input, and therefore can only records in mono. To be safe, we would simply connect the L/L+R output of the keyboard to the input of the audio interface using a patch cable. A regular guitar/instrument cable would work but there are also dedicated options meant for recording equipment, which may look the same but actually use a cable of different construction.
If your instrument has very distinct Left and Right sound outputs that are not translating well into your audio interface, you may need to purchase a Stereo to Mono cable or converter to merge the Left and Right outputs into one mono output. This method of merging L/R outputs was common in the days of old tube TVs and VCRs/DVD players where the TV only had a White (mono) RCA jack for sound, but the VCR or DVD player had White (Left) and Red (Right) RCA jacks.
Remember that most dedicated Headphone jacks output in stereo. For certain headphone jacks, you may also need a 3.5mm to 1/4 inch converter as well. 3.5mm jacks and plugs are common with computers/tablets/smartphones, as well as certain guitar amps such as the Fender Frontman 10G.
Gain Setting
Once our instrument is connected properly to our audio interface, we need to properly set our Gain knob. The Gain knob is commonly mistaken as a volume control for the instrument, but the true function of the gain knob is to properly match the electrical signal of your instrument to your audio interface.
It is better to think of Gain as the sensitivity of the audio interface rather than volume. We want to set the gain just right so that the signal/sound quality is free of hiss and distortion, and volume the listener hears is loud enough. Set it too low and the resulting instrument volume will be too quiet. Set it too high and the instrument will distort, especially when playing with loud dynamics.
You can tell if the gain is too high if you are triggering the Clip or Peak LED light on your audio interface (which is usually red). If you can hear your instrument clearly and rarely trigger the clip or peak light on your device, you have set the gain level appropriately. You can test the audio quality yourself by plugging in some headphones to your interface and using the headphone volume or Direct Monitor feature if present.
Your Gain setting will vary from instrument to instrument, especially with instruments that have their own built-in volume control. The best practice is to set the volume of your instrument first, then start with the Gain knob at 0 and slowly increase it until you find the sweet spot (where the volume is good and the signal is clean). Remember to avoid triggering the Clip or Peak light as much as possible.
For guitars without active electronics/pickups, you may want to set your guitar's volume to 10 right away as volume knobs on guitars only reduce what little output the guitar offers, not boost it (think of slowly opening or closing a floodgate). If you are unsure if your guitar uses active electronics, check if it needs a 9V battery. If it uses a 9V battery, it has active electronics.