One of the most important things to understand if you are operating any kind of sound desk whether in a live or studio environment is the Audio Signal Path.

• Signal Pathway Steps
• Big Gigantic
• Signal Pathways In The Cell

The signal path is displayed as a small glowing light along the bottom of Roon during playback. It can be Purple, Green, or Yellow, meaning: Yellow indicates low-quality playback Green indicates high-quality playback. Signal Path (pictured below) shows that Roon is sending a 96kHz 24bit stereo file to the PULSE 2 losslessly via RAAT. When the PULSE 2 receives the signal, it passes through its internal amplifier which does audio crossover and EQ.

It took me a good while to see the significance of understanding the signal path on the sound desk I was using. I thought that, because there was a button for everything, I could just wing it. I could always find what I wanted and away I went. Until it goes wrong, and you can’t understand why you’re not getting the results you want from the desk.

Signal Pathway Steps

Nov 28, 2011 Signal path: Guitar Amplifier processor or processors in an effects loop. Using rack multi effects signal processors in an effects loop has many advantages in creating sound textures. The only draw back is that your overdrive sounds from the processor are more compressed because a pre amp is driving them as opposed to a direct guitar signal.

Below is a generic signal path for an analogue sound desk. It follows a single input MIC or LINE right the way through to an output. There are many different variations of signal paths getting increasingly complicated for different features of your desk. But these are the most important to understand first.

• In this diagram you can see that you have a choice of two inputs, like on most standard mixers. MIC input as standard receives a 5mV signal from a microphone. The LINE input generally receives around 1 Volt. In order to deal with this, the mixer will have microphone PREAMPS in order to boost the MIC voltage to match the LINE level.
• Directly following this input (which is not on this diagram) is the PAD button which can drop an input level which is too loud for the desk to deal with it followed by the GAIN control. This is used to give the mixer a usable and appropriate audio level depending on the level being received by the source.
• Following this input you have the option on all of your input channels to send your raw input channel to a PRE AUX SEND. This bypasses your settings you could have put on your main mix, and could be used for an effect free, EQ free on stage monitor or a clean mix send to a recorder where you want to add your EQ and effects afterwards.
• Sometimes next to the input on the back of your mixer you’ll have another jack socket labeled INSERT. The insert, as you can see in the diagram above, is for any external signal processing devices you may have. Such as an external EQ or EFFECTS RACK. This port uses a balanced jack cable in order to come out of the desk and back into the desk on the same port. This is usually automatically detected by the desk and opens the switch to prevent the signal not bypassing the standard route.
• At this point on a mixer is where they all differ in their paths and functions and features. In this case the desk gives you the option to bypass all processing after this point and go straight to a DIRECT OUTPUT. This could be useful if you were using a desk running pre-mixed audio through a sound card or from a CD, preventing you from accidently adjusting EQ or knocking an input level.
• Following your main signal it then runs through a simple 3 or 4 band parametric EQUALIZER.
• After your EQ you have your CHANNEL FADER which adjusts (if chosen) the level of the signal sent to your outputs.
• The next signal split in the path is the POST AUX SEND. This is one of the final points in the chain that allows you to split away before the end of the path. This retains the channel processing before sending it to an output.
• The very last adjustable parameter is the PAN. This allows you to set a preference as to which side of the main stereo mix you would like the signal to be sent from this input.
• This is the point at which you have the MAIN OUTPUT GRID. This is where you can choose which output you would like to send your processed or unprocessed signal to. Each vertical line represents a separate output, whether it is an AUX, BUS, main STEREO L or STEREO R.
• If you have chosen your output to go to main STEREO L and STEREO R these will then run through your MAIN FADER, before going to your amplifiers and then speakers. The remaining output all go direct to amps and speakers.
• Take note of the labels on the aux output in the example and follow the signal path to see how this is achieved.

I hope this proves to be a help in fault finding and general use of your sound equipment.

For any questions, get in touch!

Thanks, Pete

In this episode Shahriar takes a look at a non-functional R&S FSEK 40GHz spectrum analyzer. The instrument’s LCD screen back light no longer works and the front glass is broken. Furthermore, no testing can be done until these problems are resolved. The CCFL tube is replaced with an LED counterpart and a new front panel glass is also installed.

Big Gigantic

Signal Pathways In The Cell

After power on it becomes clear that the instrument has other defects. The internal PLL is unlocked. It is observed that the OCXO module is cold and potentially not working. Examination of the LO board shows a bad inductor on the DC filter side. After this problem the instrument operates correctly but only for signals below 7GHz. After further testing it is discovered that the YIG tuned filter on the pre-selector path is not tuning at all. Eventually the fault is traced to some operational amplifiers on the YIG driver board. The repaired instrument is verified for correct operation.