My understanding of microphones and audio says this myth is not true. I’ve been told by knowledgeable experts that mic sensitivity is linear below physical clipping regardless of the transducer technology. I actually asked this question some time ago over on rec.pro.audio – a usenet discussion forum where professional audio engineers hang out. Some of their responses were rude, but they basically established that preamp gain is all that is required to match sensitivity between a dynamic and a condenser mic. Here’s a link to that thread.

Now I believe those guys. I thought it might be interesting to devise a demonstration of sorts, by plugging in a dynamic and condenser mic, playing a reference tone through a speaker in front of the mics, then adjusting preamp gains so the levels match. Then I could generate a quieter and quieter test signal by walking away from the mics making noise. Recording this diminishing sound with both mics would tell me if one could “hear things” the other could not.

Oh No!! Is the Myth True?

To my amazement, when I did conduct a demonstration for myself, I could hear more distant, quieter sounds on the condenser mic. It seemed as if the myth was true.

I knew the error was not the physics or engineering of mics, but rather something I had overlooked in setting up my test. After a day or two of research and pondering the light came on. I realized that the different pickup patterns of the two mics made my calibration procedure wrong. I was calibrating for direct, on-axis sound, but I was measuring diffuse off-axis sound. I needed to do the calibration using only the diffuse sound field, which meant moving the speaker some distance from the mics during the calibration.

A Better Test Design

At this point I also figured out that I didn’t have to move the noise source to reduce the level of the test signal, I could create test tones that got lower and lower in level and play them back from the same spot as the calibration (well, duhhhh).

Here’s the result. For the best fidelity, here’s 45db-66db-xt.wav. Or if your connection is a bit slow, the compressed version is 45db-66db-xt.mp3.

You’ll need to download one of the files and pull it into a player that can select only the right or left channel. The mic in the left channel is the condenser, a Shure KSM141. The mic in the right channel is a dynamic, the Shure SM57. This is a little excerpt from the demonstration recording. I selected the area from -45 to -66 dBFS, which is where the test tone slipped into inaudibility. I raised the level of these files substantially and there is plenty of broadband noise, so be careful not to play them too loudly. The condenser mic is in the left channel, the dynamic in the right. Listen to first one side, then the other, and see if you can hear tones at lower levels from one mic or the other.

Conduct Your Own Demonstration

If you’d like to conduct this demonstration with your own mics and room, all you need is a calibration tone and a test tone series. You can generate the calibration tone in most audio editors, and you can download my test tone series.

If you can’t figure out how to create a tone in your favorite audio workstation software, download Audacity and install it (I recommend the Beta 1.3.xx or later version). Start Audacity and choose

Generate | Tone

then fill out the Tone Generator form:

Waveform: Sine
Frequency (Hz): 1000 (a 1 Khz test tone is the normal industry standard for basic testing)
Amplitude: .6 (a very loud long 1 Khz tone can damage your speakers and possibly your ears)
Duration: 600 seconds (10 minutes should be enough)

Click OK and you’ll see a strange solid waveform. That’s your calibration tone. Just export it from Audacity:

File | Export
Save as type: (either MP3 or WAV Microsoft signed 16 bit PCM)
(Choose a directory and file name)

You can download my test tone file here. The test tone file contains volume level announcements and 1000 Hz tones starting at -9 dBFS and going down to -90 dbFS in 3 dB increments.

Here’s a screen shot of the test tone file:

Mic sensitivity test tone in Adobe Audition 3

and a sample of the tones, starting at -9 dBFS and going to some of the lower level tones:

To conduct your own demonstration, connect two mics to your recording system. Place the mics at least 6 feet from the speaker, then play the calibration tone. Adjust the preamp gain so the two mics show the same input levels. Do this very very carefully, this is the most critical step in the process.

Next, simply play the test tone file while recording the two microphones. You’ll want to wait until a quiet part of the day, and be prepared to sit very quietly while the test file plays. When you’ve completed recording the test tone sequence, listen to one of the tracks you just recorded. When you can no longer hear the test tone, switch to the other track (other mic) and listen again. If your experience is like mine, the test tones will fall into inaudibility at the same level for both mics.

Better Recording By Knowing Our Tools

Mics are fascinating devices, but they’re engineered objects in the physical world. We can make better use of them if we have a better understanding of the way they really work instead of relying on incorrect assumptions and erroneous analogies. In the past audio testing required lots of expensive dedicated equipment, but now with our computer audio systems we can easily perform simple but fairly sophisticated evaluations of our audio gear, and learn to make better recordings in the process.

I asked TC if they could offer a suggestion for saving my user patches, and they pointed me to Midi-Ox as a tool that can capture and restore MIDI information. Since I’m nearly totally ignorant of MIDI, I ran into a few issues but I’ve now succeeded so I thought I’d share what I’ve learned.

Hardware

The hardware you’ll need are a MIDI port on your computer (actually two of them, one for input and one for output) and one or two MIDI cables. Connect the computer MIDI OUT to the G Natural MIDI IN, connect the computer MIDI IN to the G Natural MIDI OUT.

Software

Download and install the MIDI-OX software on your computer.

Start the MIDO-OX software, you should see a screen something like this:

Select Options | MIDI Devices… and you should see this, but with your own set of available devices:

Click and highlight the input and output MIDI devices you hooked to your G Natural earlier. Click OK.

G Natural

Here we come to a possible gotcha of the first order. The 1.03 software update is advertised to enable MIDI functions. This makes sense because these functions are not yet documented in the latest manual on the TC site. So I suppose users who want to save their settings before upgrading to software version 1.03 are just out of luck. Oops. Still, once you have 1.03 installed, you’ll have a way to save settings in the future.

You get to MIDI functions by starting with the Menu button. Using the Edit D knob, scroll to the MIDI selection, then press Menu again to activate the MIDI menu.

Again using the Edit D knob, scroll to PrgChg.In: and make sure it’s set to Off. If it’s On, use Edit A, B, or C to change the value to Off.

Scroll with Edit D to PrgChg.Out: and once again make sure it’s Off.

Now scroll with Edit D to Dump System (for system wide settings) or Dump Bank (for user patches).

MIDI-OX

The particular corner of the MIDI world we’re using is called SysEx. This stands for System Exclusive, and it seems to be a method for storing and retrieving configuration information via MIDI. If you’re really curious. I’m sure there are lots of great tutorials out there in webland. Regardless, we can use MIDI-OX to capture a SysEx dump from the G Natural, save it to a file, and send the dump back to the G Natch.

In MIDI-OX, click View | SysEx… and you should see this:

In the SysEx View and Scratchpad window, click Sysex | Receive Manual Dump… and you’ll see this:

G Natural

Press the Menu button on the G Natural and you’ll see a message telling you the dump is taking place.

MIDI-OX

You’ll see a byte count in the Sysex Receive message box. Press the Done button and you can view the results of the SysEx dump. The lower Display Window now contains the data from your G Natural, displayed in Hexadecimal format.

Click Display Window | Save As… to save the SysEx dump to a file of your choice.

Restoring Saved Settings

To restore your settings, simply activate the SysEx window and click File | Send Sysex file… and navigate to the file you saved in the previous step. You don’t have to take any action on the G Natural except to have it turned on and connected to your MIDI port.

In Conclusion

Hopefully this writeup will help other G Natural users. Even though I still enjoy the great sounds and control provided by the G Natural, I’m a little disappointed that I had to figure this procedure out on my own, and gather the tools myself. I’m also disappointed that an update to the manual has not been provided to go along with the software update. We’re once again operating our machines without accurate documentation. And finally, I expected to have a computer based patch editor available when I bought the G Natural. I had one with my much less expensive Yamaha MagicStomp, so I’m really unpleasantly surprised to find that TC Electronics does not provide one. A proper editor would make saving and restoring settings a snap, and make creating and configuring patches a lot easier as well.

TC Electronics has setup a forum area where we can share experiences and possibly encourage TC to expedite updates to the documentation and to provide a patch editor. I hope to see you there.

How do I record my guitar so I can judge my progress (or lay down a rhythm track or even make a CD just for family and friends). I have a pickup in the guitar, I don’t need great quality, and I don’t want to spend a lot.

Since this person is posting on an internet forum, I will assume they have a computer. If it’s a PC type, it almost certainly has some kind of built-in soundcard, with at least a mic input. So all we need to do is hook the guitar pickup to that mic input and use some sort of program to capture that input and save it to a file. It just so happens that there are some very effective recording programs available to download for free, so that leaves as our only problem some way to connect the guitar pickup to the mic input. And here it is:

This is a 1/4″ phone female to 1/8″ mini male adapter. A normal guitar cable like the one just above the adapter in this picture (male 1/4″ phone plugs at both ends) fits into the hollow side. The pointed side plugs into the mic input of the computer. It costs about $4.00 at any store or web site that sells electronic geegaws (like Radio Shack). This is all you need to connect your pickup to your computer (assuming you have a guitar cable).

Now, on the software side what are the options? Unfortunately, the built-in Windows Sound Recorder is not very useful. It’s limited to about 1 minute of continuous recording without intervention. There are not effects or editing features, no click track or metronome, no metering, and certainly no multitrack overdubbing and mixing.

The easiest free program I’ve found is Audacity – it’s a little clunky but it is full featured. It includes plenty of editing capability and built-in effects, and you can save your recordings to various formats like .wav for burning to CD and (with some free extra software) to .mp3 for your portable music player or web site. I’ve used this little adapter and Audacity to record new song ideas on our laptop when we’re traveling. I’ve also used it to create practice loops when I’m trying to nail a tough section of a new song. Compared to a decent microphone, preamp, and audio interface these recordings are fuzzy, noisy, and crude, but they do the job, and the price is definitely right.

Here’s one verse of an old Hawaiian song, “No Ke Ano Ahiahi,” recorded as a solo guitar instrumental using the the 1/8″ mini plug adapter and Audacity.

And here’s the same track with some reverb added.

Obviously these are not “major label quality” recordings by a long shot. The direct output from a pickup is not very close to the natural acoustic sound of your guitar. But we’ve looked at a tool that can help get your pickup based recordings much closer to a natural acoustic sound in a previous blog entry: “Better EQ Through Software”. And, as we stated at the beginning of this entry, the whole purpose of using this simple, cheap adapter is to get simple, cheap recordings, not Grammy awards.