Topic: MIXERS: Question about "Trim" controls (I am missing something fundamental here)

[Roving Sign]

Ok - I must have a fundamentally flawed understanding of audio levels...

here is something I dont seem to understand...

Trim controls...I dont understand how the are marked relative to how they work...

It seems like they do the opposite of the markings...

My Yamaha - has a gain sweep from -16 to -60...clockwise rotation. Based on the markings - I would think that turning the knob clockwise would REDUCE levels...but not so - turning from -16 toward -60 adds gain...all the other knobs - EQ for example -15 to +15 - turn it clockwise to add eq gain...why do the trimmers seem to do the opposite?

What the heck am I missing here? Been doing this too long to not understand this...admittedly, I let the "peak" light be the boss and pay little attention to the actual settings...I noticed this last night running a Samson Mixpad 4 - which has no peak light...so I had to rely on my intuition and the markings on the mixer - But everytime I thought I was turning the trimmers up... I was actually turning them down. So I must be missing something.

[DSatz]

I don't know your particular mixer, and you didn't say which model it is so I can't go look it up on line. But if the channel gain increases when you turn the knob from -16 to -60, then maybe those numbers express the signal level (in dBu or dBV) at the microphone input which should produce some nominal level in a channel with that setting. In other (and fewer) words, it sets the sensitivity level of the microphone input.

For example, I noticed that someone in the Yard Sale is offering a pair of Audio-Technica AT3035 microphones. If you go to Audio-Technica's Web site you can find this specification for them:

OPEN CIRCUIT SENSITIVITY .... -32 dB (25.1 mV) re 1V at 1 Pa

So maybe the idea is that knowing the above specification, you would set the trim pot to -32 on any channel where you're connecting an AT3035, and so on. If that's the intended logic, and if that procedure is carefully followed, it would make the "0" fader setting on every input channel correspond to the same sound pressure level, regardless of what type of microphone is on the channel.

However, that's just an inference; like you, I'm much more used to the Mackie type of arrangement in which the dB number on the trim pot tells you the nominal gain setting of the input stage, and turning any kind of volume knob clockwise makes things louder, not softer. The Yamaha arrangement, if I've correctly guessed (whoops, I mean "inferred") what it's about, sounds like someone in the marketing department's Absolutely Brilliant Idea--for which they should be duly rewarded by keeping them the hell away from any product design ever again. On equipment to be used for live recording, where you don't normally get a second take, any controls that work the exact opposite of the way most users would expect them to work are not a welcome innovation in my book.

--best regards

[Roving Sign]

Thanks for the response - here's s a picture of the knob labeled "Gain" - clockwise adds gain, contrary to what you might think by the markings...

[DSatz]

OK, that photo matches your description, and re-reading what I wrote, I need to take back two-thirds of my rant against the designer--since as you say, turning the knob clockwise increases the gain. I'm actually relieved to see that I misunderstood when I thought the opposite was true.

But the markings around the knob are most likely what I said earlier--an indication of the input signal level which will bring the channel to its 0 level with the knob at that setting. Evidently this is a variable-gain input stage with a feedback control (i.e. the knob in the picture). When the sensitivity setting is set to a low value (a large negative number), the gain is higher since a weaker signal needs more amplification to bring it to the standard level. Conversely, when the sensitivity setting is set to a higher value (a "less large" negative number), the signal had better be stronger, since it will get less of a boost on the way in.

That is an idiosyncratic design approach to say the least. It's based on an intelligent, consistent way of looking at things--it's just not the audio world's way. If the entire audio world were well-informed enough and willing and able to do their homework enough to use that approach consistently, we would all be living in a better world than the one in which we actually live.

In this world, I know that I often need about 35 dB of gain for starters--but I don't know the approximate peak levels which my microphones are going to put out in dBu or dBV unless I borrow a calculator and do a thing with logarithms that I can't do so well in my head. So I'd much rather have a control that says "35 dB" (meaning "gain" when it says that).

But whoever designed this "innovative" scale probably got a raise and a bonus and a handshake from the divisional vice president for doing so--not to mention feeling like a hero for at least a week. Who am I to argue with the divisional vice president? I'm just a poor end user with bills to pay and a show to record, so I roll with the punches.

--best regards