Pre-amp is a very important recording equipment. Yet a lot of beginning musicians are not using pre-amp during any home recording session projects. They simply plug the microphone output or guitar output to any inputs of their mixer or audio interface/soundcard without checking if that input includes a pre-amp. If you do not know what is pre-amp, it is a piece of hardware that will amplify weak microphone or instrument signals to a line level signal. For details about these terms, read this tutorial on the difference between Line, Instrument and Microphone Levels.
Signal to Noise ratio of your Recording
One of the most important things that you should know if you are concerned about quality recording is the signal to noise ratio. The output signal of the microphone is around 2 millivolts and if the noise (assumption) is 0.5mV, the signal to noise ratio is:
S/N ratio = 2/0.5
S/N ratio = 4
Without a pre-amp, if you plug this signal output directly into an input without a pre-amp (such as line inputs); this signal can still pass an amplifier circuit like the line level control of the mixer or any recording equipment. This too can boost the signal of the input level. However there is a problem with this method. The line level boosts the signal level as well as the noise. Thus you still not get a great recording signal. For example:
2 millivolts microphone signal now becomes 20 millivolts
But the noise of 0.5 millivolt now becomes 5 millivolts
Therefore the signal to noise to ratio is:
S/N ratio = 20 millivolts/5millivolts = 4
Even though the signal is now strong, the signal to noise ratio is still the same as before. Having a strong but noisy signal is still not enough for quality recording.
Pre-amps to the rescue
One of the technical reasons why you should be using a pre-amplifier is to improve the signal to noise ratio and then apply a lot of gain to convert the weak microphone or instrument signal to line-level signal.
Pre-amps work by isolating the noise from the signal; and then boosting the signal to a line level output without adding another set of noise, coloration of the signal, etc. It is why you need to be careful when selecting pre-amps. Not all pre-amps are designed for home recording or not all of them can have great sounding results. Do your research for pre-amps that sounds very clean, very low noise and affordable. You can ask in the recording forums.
In this case the microphone signal now becomes:
Signal output from the preamp = Microphone output level x Gain
Signal output = 2 millivolts x 60 = 120 millivolt
The gain of 60 is only an approximation and may not be an exact gain used by microphone pre-amps. Since quality pre-amps does a great job in isolating noise and focusing only with the signal, this will significantly improve the signal to noise ratio of the signal being recorded:
S/N ratio =120 millivolt/5millivolt = 24
The result is that the recorded signal from the microphone (e.g. vocals) is clean and strong. If you are recording in 24-bits, the entire possible dynamic range can be filled with the vocal signals and free of noise. Subjectively, if you listen to this vocal recording in your studio monitors; the vocals sound full from top to bottom frequencies and very clear (no hiss, no noise).
4 Responses
Hi Eddie,
Thanks for those manuals, I take a closer look at your setup and it seems you only need a direct box in this case and not a preamp. TASCAM DR-100 mk2 already includes a built-in preamp that you can use. For details, I have just written a tutorial about this illustrating your case. You can read it here. I am sure you obtain lots of valuable information in that post. I also receive common inquiries on this topic so I think writing a blog post would summed up everything in one page. Cheers and Good luck to your projects.
Hi Emerson:
On closer inspection, the piano has AUX OUT for the RCA output. Is that the same as LINE OUT? Hmmm, I hope I didn’t make a mistake on that point. If I don’t need a Preamp then I can save myself an extra step. Here are the answers to your questions:
1. The recorder is a TASCAM DR-100 mk2. Here is the link to the PDF owners manual.
http://tascam.com/content/downloads/products/718/e_dr-100mk2_om_va.pdf
2. The piano has only RCA AUX OUT. No TRS. No XLR. No optical out. It has USB but that is only for transferring MIDI files to flash memory or connecting a laptop. I assume this is analog out since it’s RCA left and right connectors. I have checked the manual but it makes no mention of the RCA specs. I have been recording the piano in stereo mode. I can confirm that too since some instruments are either on one channel or the other. I can also see different sound signatures on the DAW waveform on each channel. It’s true stereo.
This is a Yamaha Clavinova CLP-295GP digital piano. Here is the link to the PDF.
http://download.yamaha.com/api/asset/file/?language=pt&site=pt.yamaha.com&asset_id=8072
Wow. I would be happy to hear that I don’t really need a preamp, if that is the case. Thank you so much for all your help. I truly appreciate your assistance and generosity. I look forward to hearing from you again.
eddie
Hi Eddie,
Wait a minute,are you planning to send line output levels to a preamp? Are you sure it is already line level audio signal? It is because line levels are already amplified in nature and if you pass them again to a preamp, it can distort the recordings (by overdriving the preamp). You only need to feed either instrument or microphone levels to a preamp. Read this tutorial illustrating the key differences between a line, instrument and microphone levels.
Some key questions here that needs to be answered before I can suggest some better ways on improving your setup:
1.) What is your digital recorder? Is it a DAW (a PC, Mac, Laptop using hard drive to store digital audio) or any a digital audio mixer with a recorder such as hard drive. If you can provide the exact brand/model of your digital recorder, the better. Or if you have the manual of that in PDF, please share as I would take a look.
2.) I got a bit confused about your piano outputs. Are there any other outputs aside from RCA (such as XLR or TRS balanced etc)? Is this an analog or digital output? Are you intending to record the piano in stereo or mono? Also if you have the exact brand and model of your digital piano , please provide so that I could take a look at the manual to see the details of their outputs. Or if you already have the manual, kindly share.
Once I entirely know about your setup, I could recommend better ways to capture the best sound of your piano. I believe (not yet sure) you don’t need a preamp here as you are already sending a line level to your digital recorder. What is probably needed is an external audio interface (USB or Firewire) to convert analog audio (if you are using piano analog outputs) to 24-bit/96KHz digital audio as you have wished to be sent to your digital recorder. But again, I am not sure if your digital recorder can accept USB, Firewire or SPDIF digital audio streams.
As you can see, you already learn lots of things by reading this blog and then actually applying the knowledge in your home studio setups.
Hello Emerson:
You were kind enough to answer some of my questions before and I wonder if I may indulge on your kindness again. I need a recommendation for a pre-amp. Let me explain my circumstances.
I want to record from a digital piano. This is my setup.
piano > LINE OUT (2 female RCA outputs) > digital recorder > DAW > CD
Now, I know you highly recommended I use a microphone but there is more here. This is an advanced piano with multi-track recording. I am able to play numerous other instruments (midi) and record them together in concert-like fashion. The result sounds like a real band or orchestra.
I believe it would be difficult to capture the complete fidelity of all the additional instruments from mics alone since these sounds are coming from the piano’s amplified speaker system. This is why I prefer to record from LINE OUT.
I agree that a pre-amp is necessary to achieve pristine sound quality. The recorder is able to capture sound up to 24-bit 96kHz using XLR LINE IN and record at these specs:
LINE 1 (Switch is set to LINE )
Input Impendance 2.5kΩ
Nominal Input Level +4dBu
Maximum Input Level +24dBu
Of course, I would need adapter cables like RCA (from piano) to XLR LINE IN (to recorder).
So, the set up would hopefully look like this in the future:
piano > LINE OUT (2 female RCA outputs) > Preamp > digital recorder > DAW > CD
I just need a simple pre-amp without additional features that I would never use. If you could recommend a particular brand or two, that would at least give me a place to start.
Thank you kindly for your time and advice. I continue to study from your compendium of knowledge.
eddie