04.21.09

Element 2 - Drum Machine, ambient

Since we decided to go with the M/S approach, there are three final options to consider - what's the best mic for the Mid? Two different things come into play here - the pickup pattern of the microphone and the frequency response. While the side mic will be the only bi-directional mic in house - a beyer M130 - there are three choices we considered for the mid.

Mid/Side configuration

CHOICES

1. Hypercardioid - beyer M160 - The M130 is designed to match up with this for an M/S pattern. Similar frequency response to the M130.

2. Cardioid - Josephson e22s - Low frequency response is deeper than either of the beyers and not as tight a foward pickup pattern as the M160.

3. Omni - Earthworks T30C - Low frequency response is deepest of any of these.

All three microphones were recorded using the FMR RNP as their pre-amp. We tried to keep the balance between the mid/side as close as possible between them. We also tried to keep them the same volume level. Note that the ratio of ambient vs. direct is higher here than it will be for the final recording; we wanted to exagerate the effect so that we could really hear the differences.

RESULTS

The sound clips here are again "labeled" with the computer voice. The first one takes the first two minutes of the song, the second one takes up the last two minutes where the double bass drum is prevelant.

Drum machine - M/S patterns, 3-way comparison (start).

Drum machine - M/S patterns, 3-way comparison (end).

It's tough to distinguish - how much of the difference between these is due to the pickup pattern and how much due to mic's response. To my ears, oddly, the cardioid has the tightest stereo image of the two, when I would think it should be in the middle. The omni sounds the widest and the hypercardioid is in the middle.

DECISION AND NEXT STEPS

Since it's tough to isolate which factor is responsible for the sound, I closed my eyes and just tried to figure out which sound I liked the best - the e22s. The snare drum seems especially sharp with this mic. Next up, then, is taking a look at the timing difference of the delay mics.

Ambient Mic Delay

This next part is studio trickery, plain and simple.

When we hear a sound in an enclosed space, we the first thing that we hear is the sound directly coming from the source (assuming there's a clear path). Then, after a slight delay, the reflectoins of that sound begin to arrive at our ears. It may be that this slight delay is one of the things that clues us into the fact that the reflections are not the direct sound, and so the delay helps provide a sense of spaciousness.

Keeping this in mind, the Stereo Soundbook tells me that Y. Ando's experiments show the following - music listeners tend to prefer the sound of a slight delay in music. That is, Ando's listeners liked the original sound of music when it was followed by a short (12 to 30 ms) delayed repeat of the same music. The sense of spaciousness is reported as pleasing.

Other research - termed the Law of First Wavefront by Cremer - shows that people can sense this delay at nearly 1 ms, but that it's not heard as a discrete echo until the delay reaches about 35 ms.

So, what does this mean? Well, we can delay the sound of the room mics vs the direct sound from the drum machine to increase the sense of spaciousness in a way that will sound pleasing. The question is - how much?

CHOICES

We delayed the mics in 5 ms (for milli-seconds, or 1/1000 of a second) increments. The room mic is about 9 feet away from the source and so is already experiencing a natural delay of about 9 to 10 ms. This means we should start to hear the sound become an echo (something we want to avoid) once the additional (artificial) delay reaches around 25 ms. To really hear this, our increments go from "zero" (meaning no artificial delay added to the room mics) to "35" (well into the range when we should hear an echo). We'll have to pick something in this range.

Although we decided above that we liked the e22s, I ran this experiment using the omni pickup mic. No special reason why.

RESULTS

Drum machine - ambient delay, 8-way comparison.

The delayed sound does more than just provide the psycho-acoustic effect noted above. The delay of the sound waves interacts with the original sound to emphasize different frequencies more than others depending on how long the delay is. In other words, notice how deep the bass drum sounds on the 20ms part. It sounds like the drums are tuned to different settings with the delays. But the original signal (and even the recording of the delayed signal) are all the same - it's just a timing difference that seems to create a difference in tone.

As expected from the results of the reported experiments, 30ms (and definitely 35ms) are too long. The percussive starts of the bass drum, sticks and closed hi hat all begin to sound like a stutter.

DECISION AND NEXT STEPS

The 20ms delay gives a nice deep sound to the bass drum, while the effect of the delay is prominent but not obvious. We'll set the room mics for a 20 ms delay.

Up next - mic placement in the room, and then finishing the drums by selecting the preamp for the mics.

In this corner, the bi-directional beyer M130.

And in this corner, the contenders for mid-mic champ-ee-uhn. L to R - beyer M160, Josephson e22s, Earthworks TC30K.

Another DAW screenshot, this time for the delay experiment. Notice the stepped beginning each of the tracks, knocking them each back 5ms from the one above. That's the only difference - the audio file for each is the same.