Tone Deafness (Amusia) and Other Causes of Persistent Pitch Problems
We have all heard individuals who can't 'carry a tune'. They are the people whose attempts at vocalizing are usually met with laughter, mockery or criticism, as well as insensitive comments like, "Don't quit your day job!"
For the person who desires to have a good voice, however, this inability to sing a melody correctly is likely to be a source of great frustration, embarrassment and shame. The voice, unlike all other instruments, comes from within the singer. It is very personal for most people, and when that voice is perceived by others as being unpleasant or deficient in any way, the individual often internalizes these criticisms and takes them to heart, as though it reflects his or her own worth as a person.
The term 'tone deaf' tends to be applied indiscriminately to a constellation of music processing, perceptual and production deficits, which leads to a lot of misdiagnoses (many of them being 'self diagnoses'). In reality, though, there are few truly tone deaf people - it is estimated that only between two and five percent of the population is medically tone deaf - and there are varying degrees and types of tone deafness.
Many people who often hit sour notes or whose singing voices are simply not good inaccurately diagnose themselves as being tone deaf. However, a person who simply sings off key, even frequently, may not be truly tone deaf, by medical definition, as there may be numerous other possible reasons for his or her 'pitch poorness', which I will list and explain shortly.
THE CAUSES OF TONE DEAFNESS
Most truly tone-deaf people not only do not enjoy music, but they also have trouble understanding what makes it special to everyone else. If they are unable to distinguish between musical notes that may differ only slightly - by a semitone, for example - these people may not be hearing music as 'tone hearing' individuals do. If differences in pitches are not perceived, then the melody of the song is also not distinguished, and therefore sounds uninteresting. This is likely to be a source of confusion and frustration to some because they may feel as though they are missing out on something that is widely appreciated and enjoyed by most everyone else in the culture.
Tone deafness, which is sometimes also called 'tune deafness' and is medically known as 'amusia', is a term that covers deficits in four conceptually distinct domains: musical perception, production, memory and the loss of symbolic manipulation skills. It is characterized by a cognitive inability to discriminate between pitches (musical notes) - a lack of relative pitch - to remember melodies long enough to be able to reproduce them vocally after hearing them, to accurately match the pitch of the voice to that of another singer or musical instrument, or to identify changes in melody, despite having normal hearing. It is an auditory processing disorder in which the internal hearing of the individual lacks the ability to recognize when his or her pitch deviates from the desired note to be sung.
The etiology of these perceptual deficits is poorly understood, but it appears that they can result from organic trauma, such as a brain injury, or some combination of genetic and environmental factors. Research also shows that tone deafness is largely hereditary, but these roots in heredity may be little more than parents who don't appreciate music or who don't sing well failing to expose their young children to music, and so the cycle continues. If they feel as though they don't have the 'gift of music' to offer to their children, they will simply come to accept that music is not all that important a skill in life and expect their children to draw the same conclusions.
While normal brains process sounds in a series, with the front and parietal cortices receiving signals that have been processed previously in the auditory cortex, the tone deaf brain has a disrupted path for this information, routing the two regions in parallel and independent pathways. Thus, information about the wrong note never makes it to the auditory cortex, while the information that does arrive at the front parietal cortex is never consciously recognized.
Although someone who is tone deaf cannot 'feel' the difference between two notes in a song, his or her brain is actually able to perceive that difference. However, there is a dissonance between registering a wrong note and the person's awareness of the wrong note. In other words, although the brain itself might be able to acknowledge the difference between changing notes, the individual will not generally be aware that he or she is singing the wrong notes. Some tone-deaf people believe that they are actually singing the correct melody of a song, until someone else tells them differently. (Even then, they are usually not convinced that their singing is as off key as they've been told it is.)
In a broader definition of the label, being 'tone deaf' often doesn't refer just to poor hearing, but also to poor singing. A study by cognitive neuroscientists Pfordresher (State University of New York at Buffalo) and Brown (Simon Fraser University) showed that poor singers were significantly worse than good singers at vocally reproducing notes but equally accurate as good singers at recognizing or identifying changes in pitch. This shows that while the tone deaf have the ability to hear differences between musical notes, they do not have the ability to produce good music. This means that when a singer is truly awful, the problem may be more than just faulty perception.
Pfordresher and Brown's research has also shown that most 'pitch poor' singers are more than just a little off when asked to repeat notes, whether they are a few notes in sequence or just a single note. They are typically off by a semitone or more, therefore singing a dramatically different note than what they are hearing. In studies, they also performed worse when accompanying someone else, unable to match a simultaneously presented pitch.
This study concludes that neither amusia (tone deafness) nor poor perception of sound are likely to be the cause of bad singing. Otherwise, bad singers would also be bad listeners, and good singers would be good listeners. In the general population, most bad singers can discern musical notes just fine. It may not be bad memory, either, since the tests in this study consisted of very short 'tunes' of no more than four notes and also accompanying a professional singer on a recording. Bad singers still sang badly. Poor motor control doesn't necessarily explain the difference either, since bad singers have a similar vocal range as good (untrained) singers.
What bad singers don't seem to have is the coordination between music perception and music production. Tone deafness seems to be a case of poor voice-ear coordination. In other words, bad singing and poor pitch are, more often than not, the results of poor vocal technique, or the inability to use the vocal instrument properly.
SOME CAUSES OF PITCH ERRORS
A common mistake is confusing or associating all persistent pitch problems with tone deafness. In the case of people who sing poorly, their poor music perception may be caused by a number of factors, including bad hearing, poor memory of the notes that makes them forget the notes quickly after they have heard them and then can't sing them back accurately, and poor control of the vocal system that prevents their ability to produce a note, even when they can hear it correctly. If the individual is able to hear the sound and knows what sound he or she wants to produce but can't seem to imitate that sound or reproduce that specific pitch at will, he or she may not be tone deaf, and may be aided by vocal training. If the individual recognizes when he or she has hit a sour note, then tone deafness is likely not the problem.
Some researchers have hypothesized that some people who are not medically tone deaf sing poorly because they haven't ever made the conscious effort to learn, since singing isn't a necessary skill in life. Whereas most people begin singing as young children, 'pitch challenged' individuals may simply have never tried. Without regular practice, the singing voice fails to develop to its fullest potential.
Lack of early exposure to music also seems to limit the individual's ability to develop the voice. The would-be singer hasn't been exposed to a variety of musical styles, harmonies, tone, etc. to ingrain into his brain the musical theory that enables an individual to hear intervals, perceive subtle acoustic changes, etc..
Other singers become psychologically wounded by criticisms and mockery that they may have received in the past. To avoid hurtful defeat and to prevent further humiliation, the singer becomes the first to run himself or herself down and declare that he or she can't sing. It can be very difficult for a person to confront all the painful defeats that he or she has experienced in being labeled tone deaf or in being called a terrible singer or someone with no musical talent. Oftentimes, in these cases, the individuals are too loosely diagnosed as being tone deaf, but not before the label has already emotionally affected them. It then takes a lot of courage and motivation to work on the problem. It is simply easier and less emotionally painful for the individual to avoid singer whenever there is a possibility of being heard.
I know a singer, for example, who was once criticized for singing Silent Night off key in the back seat of the family car as a child, and then spent many years actively avoiding being heard while she sang because she was terrified of being told to be quiet, or of being made fun of. Even though this singer had already sung numerous solos and could sing fairly well at that young age, she was so sensitive, shy and self-conscious, that this order to be quiet, given by a tired and insensitive parent, seriously affected her self-confidence and self-esteem for several years. She lost the courage to attend auditions, perform solos and even sing around the house. Fortunately, she eventually decided to begin taking voice lessons and return to singing in public, although she still shies away from being heard while singing casually and unrehearsed.
Another common explanation for pitch errors relates to another type of psychological 'hang up'. Many untrained singers have a 'comfort zone' in which they prefer to sing, usually in the middle and lower parts of their ranges. If the pitch of the song or vocal exercise starts or rises at any point above this comfortable and familiar range of notes, the singers get nervous, self-conscious and doubt their ability to hit the higher notes. They then attempt, either consciously or subconsciously, to begin singing a few notes below the correct pitch. (I used to teach a student who would unintentionally sing harmonies all the time. She wasn't usually off key; she simply wasn't singing the same notes that I was playing on the keyboard, even when I played only the single notes of the melody line, rather than a chord.) Although they know that their pitch is off, they can't seem to muster up the nerve to try to sing any higher than they are psychologically comfortable with.
TECHNICAL CAUSES OF PITCH ERRORS
In many cases, 'pitch challenged' singers have developed severe constrictions of the vocal tract that have been present for many years, including in their speaking voices. (These constrictions are less noticeable in the speaking voice because speaking tasks occur very rapidly, notes are not sustained and speaking pitch is limited.) Sometimes this tension has been present for so long that the individual can no longer feel it. These constrictions of the vocal tract make the singing voice sound even worse because tone is made unpleasant. (I explain this concept more fully in Singing With An 'Open Throat': Vocal Tract Shaping.) When I work with severely 'pitch challenged' individuals, this is probably the most common explanation for their pitch problems. After some work on releasing these tensions, improving articulation patterns and managing the breath more efficiently, most of these symptoms of 'tone deafness' disappear.
There are often psychological reasons for these tensions, including self-consciousness or a lack of confidence regarding the voice. If people are self-conscious about singing in front of, or even along with, others, they may become nervous and begin hitting sour notes. These pitch errors simply reinforce their belief that they can't sing well. When they have experienced enough discouragement because of their voices, they lose confidence in both their voice and their hearing. (They no longer trust their voice or hearing.) Hearing then becomes disconnected with their voices, and such singers cease to correct the way that they sing by means of their hearing. From this point on, confidence can rapidly decrease.
A very common cause for persistent pitch errors that I observe in my new students is the incorrect navigation of register shifts. Untrained singers often fail to make the necessary laryngeal adjustments as pitch mounts, typically carrying the lower register up too high. (This is referred to as 'static laryngeal function'.) When these adjustments aren't made gradually and skillfully, the singer reaches the top of the lower register and can't seem to flip into the next register or hit the next series of pitches in the scale. Like hitting a proverbial wall, they get stuck at the same pitch and can't seem to sing any higher because the vocal folds aren't stretched enough and the larynx isn't pivoting correctly to produce the desired note. If the singer finally gets the larynx 'unstuck', a severe register break, in which the voice is shaky, wobbly, weak or wavering uncontrollably in pitch as it unskillfully 'flips' into the next mode of laryngeal functioning, usually occurs. (The voice, especially in the male singer, will often sound unpredictable, as though it is still going through puberty.) A study of vowel modification and vocal tract relaxing and opening almost always eliminates these problems, enabling the singer to smoothly transition into the higher register without a noticeable register break or a pitch error.
Poor breath management accounts for many incidences of unplanned pitch deviation. If the flow of air leaving the lungs is not steadily regulated, as when the singer moves suddenly or attempts to 'support the tone' by rapidly and forcefully thrusting the abdominal wall inward and upward, not only is the tone of the voice affected, but pitch might be, too. Whenever a sudden and unexpected burst of air meets the fully approximated and vibrating vocal folds, the amount of subglottic air pressure is dramatically increased. The vocal folds will typically respond by pressing together more firmly to increase their resistance and/or vibrating at a faster rate, which causes the pitch of the voice to rise unintentionally. When the amount of air being pushed through the glottis is unpredictable, so, too, is pitch. Singers who hold in the air briefly before producing voice are very prone to pitch problems at the onset of sound due to the excessive subglottic pressure that has built up while holding the breath. Training in appoggio breathing technique, which aims to decrease levels of subglottic pressure by maintaining the initial posture of inhalation, thus encouraging a delay in the rise of the diaphragm, will improve the steadiness of the airflow, tone and pitch.
Yet another technical error that leads to pitch inaccuracy is a poor onset of sound and unskillful releases of the tone. Some singers will struggle to begin a note precisely at its pitch centre, but will be able to promptly make subtle pitch adjustments afterwards, as when the singer 'scoops' up to the desired note. The reasons for an imprecise onset are many. In some cases, a singer might second guess herself when beginning a musical phrase, especially when that phrase begins on a high note. In other cases, poor pre-phonatory tuning - how the singer adjusts the vocal tract prior to phonation in preparation for the note to be sung - may be to blame. Frequently, pressed phonation, in which the glottis is too firmly closed after inhalation and just prior to producing voice - this is often accompanied by supralaryngeal squeezing or constriction - can explain why a voice's pitch is 'off' at the initiation of the note, as excessive subglottic air pressure is created when the vocal folds are pressed too firmly together, and then excessive amounts of force are needed to 'blast' the glottis open and set the vocal folds vibrating. Pressed onsets of sound are characterized by a very abrupt, harsh and loud sound at the beginning of the note, which may or may not continue to affect the remainder of the sung phrase. When the onset is too firm, and the subglottal pressure blasts through the glottis, it tends to cause a raising of the intial pitch as the vocal folds are occupied with resisting the excessive and forceful air, rather than with accurately tuning for pitch.
Releases of the tone (offsets) that are either too hard or too soft may also cause unwanted pitch excursions. In a hard release, the singer attempts to stop the tone by pressing or squeezing the laryngeal muscles together, rather than fully abducting - opening - the glottis and returning to the posture of inhalation (i.e., the glottis fully open, the larynx relaxed and lower, etc.) in preparation for the next breath renewal. When the glottis is firmly closed in this manner at the end of the note, there will typically be an audible 'grunt' from the abrupt cutting off of the airflow, and then a noisy 'puffing off' of the excess air, whose pressure has built up. In a soft release, the singer is slow or 'sluggish' to open the glottis at what should be the clean termination point of the note. Very often, the soft release will produce a pitch that falls. The singer's next breath renewal may be noisy because the laryngeal muscles have not returned to the open and relaxed position that they should assume at the time of inhalation. In addition to learning how to relax the hyperfunctioning laryngeal muscles that tend to squeeze, learning to accurately determine how much air will be necessary for a given vocal task, and then taking in only the required amount of air to begin with is also key in learning to control the onset and release of sound. An onset, (or 'attack', as it is sometimes called) and a release that are gentle but precise and well-coordinated, or 'balanced', will produce better initial pitch and tone, and help to maintain a healthier voice.
'Overshooting' a pitch, especially when the interval between notes is large, happens quite frequently with some untrained singers, who make overly dramatic adjustments to their vocal tracts in order to sing a note that is perceived as being significantly higher or lower than it is in actuality. These singers usually know and can hear in their heads which note they are 'aiming' for, but they try too hard to move their voices. Practice with singing a variety of intervals and 'moving' or sliding the voice slowly then, after some time, rapidly between notes of varying intervals will usually help the singer develop more familiarity with the sensations associated with these laryngeal adjustments.
Singers will also fall flat on notes in a melody that descends, or on the last note of a phrase because they make premature adjustments to the vocal tract in anticipation of the next breath, note or line in the song. Rather than completing the note precisely and maintaining a consistency in the vocal tract until that note has completely ended, they allow for a 'sloppy' release or decay of the note.
A wide-swinging vibrato or a vocal wobble may lead to pitchiness or to the perception of pitchiness, as it makes it difficult, if not impossible, to identify the pitch centre when the fluctuations of the note are too slow and cover too broad an interval. A singer who tends to manufacture vibrancy through muscular effort (e.g., a quivering jaw, a wagging tongue or a shaking diaphragm) or other incorrect methods will not be able to achieve an acceptable oscillatory rate - it is impossible to make these larger muscle groups shake or vibrate as fast as a naturally occuring vibrato would. As a result, every movement of pitch away from the actual written note will be noticeable.
Finally, a very imbalanced tone - that is, a tone that overemphasizes certain formants (overtones) and underemphasizes others - may produce a sound that seems to be slightly off in pitch. While the singer may actually be producing the desired pitch, the missing overtones will cause the listening ear to recognize that something within the voice's production seems 'off', and that 'something' is likely to be labeled as pitch. In actuality, the fundamental frequency - that which is associated with the pitch itself - may be correct, but the resonance frequencies (i.e., the overtones) are 'clashing' with each other, creating a sound that is perceived as being slightly 'off', although the listener may not be able to place his finger on what about the voice seems off. (This is truly an acoustic phenomenon, and involves the 'perception of pitch'.) Learning to 'tune the formants' of the voice by making precise adjustments to the vocal tract for every vowel at every pitch (through a study of correct articulation and vocal tract opening) will invite more balance into the resonance of the voice, and thus stabilize this 'perception of pitch'.
DIAGNOSING AND ASSESSING THE DEGREE OF TONE DEAFNESS
One option for the singer is to take a test to determine whether or not he or she can be medically diagnosed as tone deaf. The Harvard Health Letter refers readers who wish to test their ability to perceive music to an online test (as part of a study) developed by researchers at the University of Newcastle-upon-Tyne in England at http://www.delosis.com/listening/home.html.
This test, however, is limited in that it only provides scores that indicate whether or not an individual accurately perceives changes in pitch. It doesn't offer an explanation for why pitch problems may be occurring. It can't, for instance, diagnose technical problems that may be correctable through vocal training. Some individuals who receive low scores might become discouraged and feel hopeless, and become convinced that having a good voice will forever be out their reach. Still, taking the test may be beneficial as a starting place, so long as the individual who takes it understands that a low score doesn't necessarily mean that he or she will never be able to learn to sing on tune.
When I'm doing an initial assessment of a student who has severe pitch matching difficulties, I usually work in reverse. Instead of having the student attempt to match the pitch of my voice or that of a musical instrument, I'll have him or her sing a note of his or her choosing. I'll then sing a note, either the same or different than the one that he or she is singing. Then, I'll ask if my pitch was higher, lower or the same as his or hers. I'll usually ask the student to sing different pitches, some high, some low, but one at a time. This test helps me to determine whether or not the singer can physically produce a variety of pitches (and if he or she already has some vocal range to work with). A truly tone deaf individual will likely produce the same pitch each time, or close to it, and that pitch will usually be within his or her normal and comfortable speech-inflection range.
I'll also have the student briefly sustain a note of his or her choosing (if he or she can sustain a note) while I begin to sing just slightly flat or sharp and alter my pitch continually but slowly. I'll have the student wave or signal to me when my pitch finally matches his or hers. This sometimes requires tuning the overtones of my own voice to match those of her voice, even if hers are imbalanced. (Teaching the singer to properly balance his or her resonance can come later, after the assessment - when the real training begins.) It is much easier for me to adjust my pitch and resonance to match that of the student's than expecting the student who is struggling with pitch to match his or her voice to my pitch and resonance balance.
In the meantime, I am also listening to how well the student's voice moves during speech - how much inflection is present - and if I can hear any indications within his or her speaking technique of what might be affecting his or her ability to accurately reproduce pitch. In the female, I would expect some of her inflection to reach into her middle register, whereas a male's voice would be expected to remain within the chest register during speaking tasks. A speaking voice that moves well between pitches indicates a degree of laryngeal flexibility as well as the presence of some natural musicality that simply needs encouragement and development.
THE CURE FOR TONE DEAFNESS AND 'PITCHINESS'
Unfortunately, there is no known cure for tone deafness. The truly tone-deaf individual - for whom amusia represents a cognitive deficit - is someone who will never be able to learn to distinguish between notes and thus correctly sing the melody of a song.
However, plenty can be done to improve and even eliminate pitchiness for those who are not truly tone deaf. The majority of persistent 'tunelessness' in individuals is curable with some ear training and vocal technique instruction. For those problems that are related to poor training, the voice and the ear can be taught to become more coordinated and function as a team. The biggest hurdle for most students - that being a lack of confidence in the voice - is quickly overcome once the singer gains technical skills and improved control over the vocal instrument. They then develop confidence in knowing that they can make their voices do whatever they want them to do and no longer feel as though their voices are out of their control.
More than a few new students of mine, aware of and embarrassed about their 'pitch imperfectness', have half jokingly told me upfront that they suspect that they might be tone deaf. Of course, some of those singers know that they aren't really tone deaf. However, equipped with no satisfactory explanation for their frequent deviations from the desired pitch, some of these students have been secretly concerned about their ability to ever hear and accurately match pitch. They worry that their dreams of becoming professional singers or simply being able to sing to their children or join a choir will be dashed by an incurable problem that affects something so crucial to singing.
It doesn't usually take long to put their minds at ease, though. In the majority of cases, it is found that technical limitations and errors, rather than cognitive inabilities, are at the root of their uncontrollable straying from the desired pitch.
The best option for a person who wants to know whether or not there is hope for him or her as a singer is to find a competent vocal instructor who will be able to listen to the student sing, and then determine whether or not he or she is truly tone deaf, or whether or not he or she simply needs to learn better vocal technique.
By correcting their singing technique, many self-diagnosed tone-deaf individuals can successfully learn to sing in tune. In many cases, this specialized vocal training involves releasing severe constrictions of the vocal tract that have been present for many years, but that the 'pitch challenged' singer is not even aware of. A skilled vocal teacher will know how to encourage more relaxation of the vocal instrument.
A voice instructor can also help a student through ear training exercises so that he or she can begin to recognize the sounds and sensations of pitch when it is both incorrect and correct. Once the singer begins to feel confident in his or her ability to hear and reproduce musical pitches, and once the singer's technique has shown some other signs of improvement, it doesn't usually take long for that singer to begin to feel more confident and comfortable with his or her singing voice. In fact, many previously self-diagnosed tone-deaf individuals are able to become soloists and establish professional singing careers.
EAR TRAINING FOR TEACHERS
A student of voice will not get very far as a singer if his or her pitch is frequently incorrect. It is the responsibility of the voice teacher to address pitch inaccuracies, diagnose their causes and then present solutions. The following paragraphs offer some suggestions for how to go about improving a student's pitch. The best way to train a singer's ear depends on the individual singer and how severe his or her pitch problems are.
One of the things that often gets neglected whenever people are trying to improve pitch is tone. If a singer's tone is overly bright (over emphasis of upper harmonic partials/formants) or too dark (lacking in upper partials/overtones), his or her tone might 'clash' with the tone of the accompanying musical instrument, making it even more difficult for the singer to hear the fundamental pitch of the tone. He or she won't be able to correct the pitch until changes are made in how he or she shapes the vocal tract and balances the tone in order to blend better with the accompanying instrument. If the teacher is able to help his or her singers achieve resonance balance (through formant or resonance 'tuning'), they might then have more success matching pitch.
Sometimes, singers find it more difficult to hear pitch within certain timbral contexts. For example, a certain musical instrument that may be used to accompany the singer may produce tones and vibrato (beats of the sound waves that are unique to each type of instrument) that do not blend well with that singer's voice or may throw the singer off. Usually, a piano's tone is good for most people, but others might have better success with an acoustic guitar, for example. I've worked with some individuals for whom matching their voice to another person's voice (who is singing with a good acoustic balance) is most helpful. Some of this might be related to their own individual singing tone, as I've explained above.
Matching to other voices with similar tonal qualities and vocal weights can also make things easier for singers to hear and reproduce the desired pitch. The struggling singer can be paired up with another member of the choir whose pitch accuracy is precise, whose vibrato is not wide-swinging, and whose voice will blend well with the struggling singer. When working with individuals who have severe pitch problems, another human voice (i.e., that of a voice teacher) is ideal because the more skillful singer can adjust his or her resonance to help the pitch-challenged singer hear when the pitch and overtones are off or on.
It's wisest to use a comfortable and 'safe' pitch when beginning to train the ear to distinguish between different musical notes. Doing so will eliminate some of the nervousness and stress that the singer might be feeling. I often start with speaking exercises instead of jumping right into singing. If the student is able to inflect the voice in precise ways, such as sighing with descending pitch or sirening, singing is just a step away. Also, stick with single notes initially, rather than expecting the less skillful individual to produce several notes of a melody in succession.
Start out playing loudly on the accompanying instrument. This will help the student feel less self-conscious about being heard and will enable the student to hear the notes and the overtones of the instrument better. The same applies if matching pitch to a voice.
Also, stick with single notes initially, rather than expecting the less skillful individual to produce several notes of a melody in succession. Avoid playing chords whenever possible. Play just the sung notes of the lead melody (one note at a time), at least while you are working with the student individually. Play the note and have her sing it while the piano is resonating. Have her listen to how the ring of her tone matches with and is compatible with that of the piano. (If it 'clashes' with the instrument, she won't be able to hear whenever her pitch is correct or incorrect, and you might need to help her balance her tone first.) Then, try playing the same note and have her sing back that note while the piano's sound is fading. Then, try playing the note and have her sing back that same pitch after the piano has ceased making the sound. This will train her to hear and then repeat, rather than always require the note as a simultaneous reference.
After the student starts to pitch match correctly more often, start adding the simplest major chord structure. Have him sing the note (e.g., middle C) repeatedly. Once he gets the pitch correct, softly play the appropriate chord. Don't let the singer get discouraged if he gets thrown off pitch at first by the other pitches in the chord. That's normal.
When you want to work through a line of melody, start with one note at a time. Then, move on to connecting two consecutive notes, then three, etc.. The student may struggle with certain intervals more than others, likely due to technical limitations. Try different vocal exercises, such as intervallic slides or portamentos, to help train the voice to move through that interval. Start by teaching just a small portion of the song, perhaps only a single line.
In most cases, difficulties matching pitch resolve on their own as the singer sings more. Singing more usually improves technique as well as comfort and confidence levels, which in turn improves pitch.
Always be patient, and encourage the singer to be patient and to persevere. It may take some time to eliminate the causes of persistent pitch inaccuracy, especially if they have affected the voice for many years.
It may seem obvious and unnecessary to mention, but avoid laughing or making insensitive comments whenever a singer makes an error in pitch. Pointing out the problem in an unconstructive manner will only make that person feel bad about himself and exacerbate any underlying psychological causes, such as self-consciousness. If you are a teacher, very matter-of-factly point out the pitch inaccuracy and have the student attempt to sing the note correctly. If the note is still off, quickly diagnose the cause so that the student can know that it is correctable with improved technique.
I advise not placing too much emphasis on pitch problems, especially if you are a music teacher or chorus director for children and pre-teens. If students or choir members are being reminded regularly that they can't sing on tune - if they are being pulled aside after class or rehearsal in order to work on their pitch individually, or if you are stopping the whole class in order to point out that their section of the choir sounds terrible - they'll become very self-conscious, discouraged and ashamed, and their love of singing might disappear altogether. Sometimes, it's best simply to appreciate their efforts and enthusiasm, grade them accordingly, and let things work themselves out in time. Again, their pitch will likely improve after they have spent more time singing and have developed a little more confidence. (Also, the vocal instruments of children are not fully developed yet, and while they should be exercised through singing and other vocalizing, not every voice develops its ability in the same way and on the same time table as other voices might. At various points in the physical development of the child, the laryngeal muscles may have more or less coordination and strength. Sometimes waiting it out for a year or two might be the best course of action.)
In the meantime, parents can encourage better development of this coordination between music perception and music production by singing along with their children more often. They can also work with their children by singing single notes and having them attempt to match those pitches and by doing slides and sirening to encourage flexibility of the vocal instrument through various pitch ranges. They can also play games and do fun exercises - such as trying to hum along to the steady, sustained pitch of the vacuum cleaner, bathroom fan or car motor (at the same pitch, of course) - that will help the child to develop a better ear for pitch while not pointing out the deficit in the child.
For other practical tips on ear training, please read the Improving Pitch: Ear Training and Harmony section in Tips For Practicing Singing: A Practical Guide To Vocal Development.