Notes randomly are higher in pitch: what things to watch out?

[JonathanPDX]

As others have said, you are probably bending the strings with your left hand. An easy way to check would be to record video of yourself playing and then watch it back, paying particular attention to the left hand. Even better, if you have another instrument like a guitar or piano available, play along to the recording and see if the pitch is off when not matched with the same technique.

 

[Low Main]

Pickup height, along with action and relief as mentioned previously.

 

[N4860]

You mentioned that you hear the dissonance when playing along with the xylo? Perhaps this is arrangement related if the xylo is playing somewhere in the same register as you. Any slight pitch that is out of tune close to the same register is going to be much more noticeable. If you only notice this when playing with the xylo but not the guitars, maybe it is the xylo causing the problem somehow?

Have you measured the tuning of the recorded notes that are out of tune? And measured the recorded isolated xylo too?

 

[Aloe]

You mentioned that you hear the dissonance when playing along with the xylo? Perhaps this is arrangement related if the xylo is playing somewhere in the same register as you. Any slight pitch that is out of tune close to the same register is going to be much more noticeable.

well, if I go octave up (and we're in octave), we're good. somehow when we're two octaves apart this is much more disturbing.

it more sounds like not a dissonance but like my low A is somewhere in between xylo's A and Bb, so if he plays any of them, they're like both not dissonant. I experienced this in different rooms, with different amps and cabs and with different basses so I blame my technique, as it's the constant here. oh yeah, I've tried several different glocks as well and checked their pitch.

p.s. the recording use case mentioned in OP was a bit different, yeah, it sounded like a dissonance between a voice and a bass. and yeah, I can confirm, the offending notes on bass indeed have a higher pitch.

 

[sunbeast]

I always play notes as hard as I would ever play them when tuning, as the pitch at the attack of your note will be the highest and will increase in pitch the harder you play- so I usually set the tuning so that my attack is just in tune and gets a little flat with sustain and never goes sharp with normal playing (having a fast/accurate tuner is ideal for this). Tuning discrepancies tend to sound the worst if the lowest-pitched instrument is sharp, but if the lower instrument is slightly flat it sounds relatively much nicer. As you've noticed, the harder you play and the more you excite the string laterally (playing parallel to the fretboard the string has more space to move without hitting frets) the sharper your note attacks will be. And of course if you are fretting too hard behind the fret you can be stretching the string slightly sharper.

A fretted guitar/bass often has tuning inconsistencies across the neck even relative to equal temperament (and even accounting for perfect technique), so while certain intervals may show to be exactly in tune across the neck it is unlikely that every note will be equally in tune due to compounding inconsistencies caused by the setup (nut height, relief, inconsistent fret heights, etc). If your nut height is too high for example, then lower register notes will tend to be sharper as you will be compensating your intonation settings for the extra height.
The harmonics of a wound string are also imperfect, so while your fundamental note may be in tune the higher harmonics in your tone can be slightly out of tune with the fundamental- this is worse on the larger strings (more winding relative to core) and gets worse as you play higher up on the neck on the thicker strings (this is a very common issue on upright pianos, where they will deal with it by dropping the low register tuning and raising the higher register tuning in order for the harmonics of the low notes to sound more in tune with the more true higher notes). This inharmonicity isn't usually a terrible issue on long-scale 4-string basses unless you have bad strings or they were installed with twisting, though it is very common on low B strings on 34" scale or less and also common on E or even A strings on shorter scales.

As far as playing along with a xylophone or glockenspiel (different instruments! which are you referencing?) A xylophone is tuned by note and doesn't rely on strings for sound, so it is possible to easily make it much more exactly in tune across the fundamentals- however the harmonics of a xylophone or glockenspiel can be out of tune with the typical harmonics of string instruments and other instruments dependent on the design of the bars (harmonics can be tuned by carving out material underneath each bar). The lower notes of a xylophone usually have resonant tubes to strengthen the fundamental pitch relative to the harmonics which reinforces the pitch, but a glockenspiel usually doesn't.

 

[micguy]

actually with guitars I don't notice it, with a xylo (glock) I do. glock is tuned to 440Hz per my tuner, so am I

OK, a little Physics lesson here (I studied this stuff in college). String instruments have inherently in tune overtones - they are harmonics of the fundamental, meaning they occur at integer multiples of the fundamental frequency. This is because most of the restoring force comes from the tension in the string the stiffness of the string is constant with respect to frequency. When a string gets big enough in diameter, the stiffness of the string starts to become an issue, so....we use a small string (for low stiffness) and then wrap winds around that small string to add mass, so the thing can resonate a low frequencies.

OK so what?

Xylophones, glockenspiels, marimbas, vibes (all those things where you hit a bar to make sound) are inherently different - the stiffness of the bar is what provides the restoring force. That stiffness is NOT independent of frequency - it's a dispersive medium, which means that the sound travels though it at different rates for different frequencies. That means the overtones are not harmonics - they are not multiples of the fundamental. If you look at the bars on those instruments, some of them have undercuts - that helps get the lowest overtones a bit closer to in tune with the fundamental, but it's not a complete fix.

So, I said before that what you were saying did not make sense to me - bass guitar is an instrument that is inherently hard to play "out of tune". Now, knowing the context in which you're hearing "you're out of tune", things makes perfect sense. Here's the truth:

YOU are not out of tune. YOUR BASS is not out of tune - it's fine. When playing with a glock/xylo/etc, however, that instrument is out of tune with itself in terms of harmonics, and when heard with your persistent harmonics which are in tune, they clash. It's not your problem, it's an ensemble problem, and there is no fix that will make the bass work better, other than to use flats, so your harmonics die quicker, lessening the time in which you can hear the clash/dissonance. To fix it as an ensemble problem, you might move the parts to different octaves to where you hear that dissonance less. As you're the bass player, and you likely want to keep the low end solid, that probably means moving the other instrument up.

 

[Aloe]

YOU are not out of tune. YOUR BASS is not out of tune - it's fine.

not really, and I can verify this. a fretted low A is sometimes a bit sharper then the open low A and I definitely can hear and measure that.

and sometimes it's okay, just in same recorded line. so, I attribute this to forceful picking and fretting.

frankly the recording situation mentioned in OP didn't involve the glock at all. a singer complained, I'm randomly out of tune when singing over my line, we've checked and indeed it was the case.

 

[Ritter667]

High string action and low tension strings makes it easier to risk pushing the fretted notes out of tune too.

 

[tshapiro]

If you are serious about dialing in your tuning, I highly recommend the Sonic Research tuners and leaving them in Always On mode. These guys are lightening fast and you can see realtime if you are sharp or flat. If you practice with one, you'll figure out the right pressure and just overall start playing cleaner. Plus, if you hear something that sounds off while you're holding a note while playing, you can look at it and determine whether you're truly off or if it's your ear.

Tip for playing live: if I see I'm a little off tune, I just give the corresponding tuning knob a little tweak in the right direction and it's usually sorts things out. No need to stop and tune up in between songs anymore.