Doc & Perry – 7/2023

Decibels what do they do? Part2

Readtime: 1-2 min

dBm, the gear that uses this standard & a little experiment.

decibel milliwatt


We talked about dBu which is used to measure voltage in this article. 

dBm is instead used to measure power. 

The “m” in dBm stands for milliwatt, where 0 dBm equals 1 milliwatt of power over a 600 ohm impedance that dissipates 0.775V. 

dBm is mostly obsolete, but we need to talk about it  because the current dBu standard is derived from dBm.

In the past systems were designed to transfer as much power as possible across very long telephone lines and it was deployed for that reason.  In the modern world we want to transfer voltage regardless of impedance as it is much more efficient. dBm and dBu values are often the same, but dBm applies only when the input and output of a devices has a 600 ohm impedance.

Gear that uses a 600 ohm input and output system is:
 -Pultec EQ

Most stuff from 50s and 60s. We recommend to always take the time to read the manual! If you own anything that uses a 600 ohm input/output transformer you might get some benefits by adding a 647 ohm resistor across its output. This could help them “drive” better whatever equipment that follows.

600 ohm adapter

BIG DISCLAIMER here before we go ahead. The following experiment might give different results to different people, this is due not only to the empiric nature of it but also varies with length of cables between equipment so do not expect a night&day difference, but give it a go and see if it works better for you.

If you have bought a Pultec, an LA-2A, LA-3A, 1176s and so on you might want to experiment by adding a resistor across it’s output to “help it drive the following device better”. This is especially true if you are connecting your 600 ohm device to a modern device that uses a 10Kohm input impedance. Pretty much anything built from the 70s onwards  uses a 10K to 30Kohm input impedance so you do not need to worry about any contemporary gear.

Adding a resistor between the output of your LA-2A and your AD (Analogue to Digital converter) means allowing as much voltage transfer between the two devices with the potential benefit of reducing some noise.

step by step guide

To do this all you need is a short XLR to XLR such as the one in the picture below.

Now source a 649 ohm resistor or the closest value you can get. Here is a table with standard values. Experiment with anything between 620 and 681. Below you see a table with the colour coding for a 649 ohm. The one in the picture below is 620 ohm. 

Solder the chosen resistor across PIN 2 and PIN 3 of the XLR.
See picture below.

impedance adaptor

Close the XLR connector back together, add a label so you do not get confused with other cables and install it at the output of the 600 ohm device you want to use it on. Job done! 

impedance adaptor label

Doc & Perry – 6/2023

Decibels what do they do?

Readtime: 1-2 min

And what are the practical applications and examples. Part 1.


decibel scale. aid to understand real life loudness versus decibel value

(dB)are a logarithmic unit of measurement. 

In sound and music, decibels are used to express the loudness of a sound.

higher decibels levels indicate a louder sound.

The human ear is capable of detecting a wide range of sound intensities, we use decibels for a more intuitive and manageable representation of sound levels.

In electronic terms (referred to voltage) this is also important when using equipment as this tells you how much you are boosting or cutting a signal.


to give you an example 

 +6 dB   = boost the voltage 2 times 

 +20 dB = boost the voltage 10 times 

  +40 dB = boost the voltage 100 times 

    +80 dB = boost the voltage 10,000 times


If you consider that your standard dynamic mic (Shure SM57) outputs 1millivolt (0.001V) and if used on a quiet source you might be setting your microphone preamps to 80dB you would be likely seeing at the out XLR of the preamps something in the region of 10V volts or 22dBu.

That is a huge amount of amplification.

There is no such thing as “free gain” and the main trade off is that gain always carries noise with it, the more you amplify the more noise you create. The only way of amplifying a signal without inducing more noise to it is to use a transformer, but more on this subject in future posts. 

The main TIP here would be to  always match the microphone type and sensitivity to the source loudness to achieve the best Signal to Noise Ratio S/N.

decibels volume unit dbu

(dBu) The “u” in dBu stands for “unloaded/unterminated” because the levels are not dependent on a specific load impedance, or termination.

Current audio gear specifies input and output levels as dBu where 0 dBu is 0.775 volts. 

This voltage is not arbitrary and it relates to an earlier standard called dBm to be discussed in another post.

The volume unit (VU) meters in a recording studio or broadcast console is offset by convention. 

When calibrating equipment, we typically use a 1 KHz sine wave at +4 dBu (1.23 volts). So when we send that to an input, if everything is at unity we would expect the console’s meter to read 0 VU.

+4dBu should be your new best friend 😉

VU meter picture

Stay tuned for Part 2!

Danton Supple Periscope Sound Experiments

Readtime: 2-3min

Top record producer shows us his unusual microphone placement to satisfy your thirst for sound exploration. The ultimate traveling without moving experience. watch the video on YouTube! 

Danton Supple is not your average run of the mill record producer.

Producer, Mixer, engineer and overall insatiable sound explorer. Danton spends his days working in numerous studios around the world, with artists from many countries. He also systematically flies back to East London to work in his beautiful studio at Strongroom. He is also the co-founder of the band Hydra.

Danton really needs no introduction. His credits include Elbow, Morrisey, Kylie Minogue, Coldplay. For Danton it’s always about the vibe and feel of a song. He works very precisely yet quickly when setting up in the studio and always looks for that immediate sonic excitement. 

Danton is not short of choices when it comes to gear and microphones. His Studio in East London boasts a Calrec Q Series Console, an insane number of microphones (U47, U67, U87 you name it) and more gear than you can shake a stick at. With these tools, he can imagine and create a new sound palette every time a new artist comes in. This makes every day sculpturing sound a fun and exciting activity.

He is also well known for his musical ear, testimony of that is the long string of credits under his belt, most of which as producer and mixer. 

Traveling for Danton is a pleasure as well as a way of discovering new talents, musical styles and working on new music. His talent does not need to be checked in at the airport but his gear does. Luckily enough for him most of the studios he works at have a good selection of gear and microphones. 

Sometimes Danton records in a space that is not necessarily a recording studio. He then needs to take the right type of gear with him and it all needs to operate from a minimalistic set up: a portable interface, a laptop and some key microphones.

For Danton getting a set of Periscopes means he no longer needs to pack more gear than he needs to maintain his sound palette, but also he can continue experimenting without relying on what he finds on site once he gets there.

The Periscope is now his go-to microphone to get an inspiring and unusual sound behind a piano or in an hallway between the live room and the control room, creating an exciting new sound to feed the musicians with as well as being the DAW track that can be manipulated later. 

The Periscope is instant excitement and throws you into an unexpected sonic space that can inspire ideas and performances ”.

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