Double Bass Help ! Fishman Platinum Pro EQ !

[Lionel Albert]

Hi !

I would like to know how the notch knob really works and what really means in and out.
I understand it's a filter but what really happens when you turn it to the left, the right ?
What's the neutral position ?

Thanks !

 

[ahbass2500]

It is meant to fight feedback. Set to Out, no notch applied (knob will do nothing). Set to In, you will have a narrow frequency EQ cut at the notch frequency (frequency is controlled by the knob).

Start with it out. No feedback, then you are good. If you have feedback, hit the phase switch. Stop here if feedback is gone. If it continues, set the notch to in and sweep the knob to find the feedback frequency. When feedback reduces or stops, leave the notch knob there.

I cannot say which direction goes to higher or lower frequency on that knob as I do not own this version. You should be able to tell when you turn the knob with notch set to in.

 

[brianrost]

There is no neutral position, that’s why there is a switch. The knob controls the frequency of the notch, not the depth (fixed at a 12 dB cut). Full CCW is the lowest frequency (45 Hz), full CW the highest (370 Hz).

 

[Lionel Albert]

It is meant to fight feedback. Set to Out, no notch applied (knob will do nothing). Set to In, you will have a narrow frequency EQ cut at the notch frequency (frequency is controlled by the knob).

Start with it out. No feedback, then you are good. If you have feedback, hit the phase switch. Stop here if feedback is gone. If it continues, set the notch to in and sweep the knob to find the feedback frequency. When feedback reduces or stops, leave the notch knob there.

I cannot say which direction goes to higher or lower frequency on that knob as I do not own this version. You should be able to tell when you turn the knob with notch set to in.

Thanks very much, does "phase" mean "out of phase" or the opposite ?

 

[s van order]

When I need to amplify, I use an on-board condenser mic with my carbon fiber cello, which is very resonant and thus pretty feedback prone. I found the Platinum notch subdued the feedback. What I did was find the volume where the cello started to feedback, and dialed the notch around while feedback occurred, until I found the setting that stopped it.

 

[bass player 53]

According to the Manual (available
on-line at Fishman Support),
the notch is 45 Hz to 370 kHz.
The guitar example shown elsewhere
puts it at 45 Hz to 1 kHz.
Full clockwise is the larger frequency.
Phase switch: down is non- inverting.

 

[ahbass2500]

Thanks very much, does "phase" mean "out of phase" or the opposite ?

Yeah. It will invert the phase of the signal, which helps with feedback.

 

[bass player 53]

Phase: down= non inverting.
Notch: 45- 370kHz. Clockwise
increases frequency.

Sorry for the double post.

 

[Wasnex]

Yeah. It will invert the phase of the signal, which helps with feedback.

Maybe; maybe not.

Comments...and this is not directed specifically at you:
1. IMHO it's actually a polarity switch.
2. The reason results vary.

a.) The phase variance between the pickup vibrations and the sound from the amp depends on the frequency and distance between the pickup and speaker.​

b.) The speaker itself will also introduce some degree of phase shift that (AFAIK) varies with frequency. Let's ignore this for the sake of discussion and assume the pickup, amp, and cab start in absolute phase. In other words regardless of the note you pluck, the vibrations of the pickup and speaker are perfectly in-phase.​

c.) It takes time for sound to travel distance (propagation delay). The speed of sound varies a bit, but in generally is takes about 1mS for sound to travel 1.3'.​

d.) Wavelength is inversely proportional to frequency. In other words the lower the frequency, the longer the wavelength.​

e.) The phase angle will rotate as the sound travels from the speaker back to the bass. Because of 2c. and 2d., the phase angle when the sound arrives at the pickup depends on the frequency and distance between the speaker and bass. Some frequencies will be perfectly in-phase and some will be perfectly out-of-phase. Most will be somewhere between in-phase and out-of-phase.​

3. Switching the phase (polarity) generally shifts the problem to a different frequency. Let's say you're getting feedback at 130hz. This could be because there are more than one resonances in the system centered at 130hz. Because of the wavelength and distance between the bass and speaker, with the switch in one position, the sound from the amp arrives at the pickup perfectly in phase, which results summing and causes feedback. By flipping the switch, the polarity of the sound from the amp is inverted, so that it cancels at 130hz instead of summing.

a. Sometimes flipping the switch will cause a feedback problem to occur at a different frequency.​

b. If the polarity switch does not help, you can try changing the distance between the speaker and bass.​

 

[Lionel Albert]

Maybe; maybe not.

Comments...and this is not directed specifically at you:
1. IMHO it's actually a polarity switch.
2. The reason results vary.

a.) The phase variance between the pickup vibrations and the sound from the amp depends on the frequency and distance between the pickup and speaker.​

b.) The speaker itself will also introduce some degree of phase shift that (AFAIK) varies with frequency. Let's ignore this for the sake of discussion and assume the pickup, amp, and cab start in absolute phase. In other words regardless of the note you pluck, the vibrations of the pickup and speaker are perfectly in-phase.​

c.) It takes time for sound to travel distance (propagation delay). The speed of sound varies a bit, but in generally is takes about 1mS for sound to travel 1.3'.​

d.) Wavelength is inversely proportional to frequency. In other words the lower the frequency, the longer the wavelength.​

e.) The phase angle will rotate as the sound travels from the speaker back to the bass. Because of 2c. and 2d., the phase angle when the sound arrives at the pickup depends on the frequency and distance between the speaker and bass. Some frequencies will be perfectly in-phase and some will be perfectly out-of-phase. Most will be somewhere between in-phase and out-of-phase.​

3. Switching the phase (polarity) generally shifts the problem to a different frequency. Let's say you're getting feedback at 130hz. This could be because there are more than one resonances in the system centered at 130hz. Because of the wavelength and distance between the bass and speaker, with the switch in one position, the sound from the amp arrives at the pickup perfectly in phase, which results summing and causes feedback. By flipping the switch, the polarity of the sound from the amp is inverted, so that it cancels at 130hz instead of summing.

a. Sometimes flipping the switch will cause a feedback problem to occur at a different frequency.​

b. If the polarity switch does not help, you can try changing the distance between the speaker and bass.​

I've got all the feedback of the Universe every time I'm touching the notch knob, I usually resolve the problem with EQ and low cut.

 

[brianrost]

As Wasnex notes, the “phase" switch found on so many preamps is really just a polarity reversal.

All feedback fighting starts with moving the instrument around looking for a spot on stage where you can get more volume without feedback. The main cause of feedback for me is playing on tiny stages where I just can’t stand far enough away from the amp. Switching polarity, using notch and high pass filters, and fine tuning EQ are my next options.

 

[Lionel Albert]

As Wasnex notes, the “phase" switch found on so many preamps is really just a polarity reversal.

All feedback fighting starts with moving the instrument around looking for a spot on stage where you can get more volume without feedback. The main cause of feedback for me is playing on tiny stages where I just can’t stand far enough away from the amp. Switching polarity, using notch and high pass filters, and fine tuning EQ are my next options.

Yes, that's true !
Outdoor

Big stage


Playing loud in a rehearsal


Everything has be done with the Fishman.

No feedback at all outdoor.

On the big stage, my bass transmitted all the orchestra and the smoke machine in my amp.
Low cut was at 100% but everything was boomy except far from the stage.

In a loud rehearsal, I feel always out off tune, it depends where I stand.
Some feedback when the others play louder.

So it doesn't only depend of where you are, it also depends of the others and the way they play.

As I said, I have never really understood how my preamp worked.

Now I understand a little bit more.