Much has been written about how the bleakness of industrial Birmingham bled into Black Sabbath's music and led to the creation of what would eventually become known as heavy metal. It has been suggested that Tony Iommi's down-tuned blues riffs, Ozzy Osbourne's inimitable wail, and the lyrical themes bassist Geezer Butler – who formed a swinging rhythm-section with drummer Bill Ward – highlighted were all informed by the band's socio-economic background. But as much as the grey gloom of England may have affected the mood of the music of Black Sabbath, Napalm Death and Godflesh, and the winter chill of picturesque Norway impacted upon the black metal of Emperor, Immortal and Ulver, the suffocating humidity and rich musical history of New Orleans, Louisiana, also played a role in the development of its metal musicians.

A veritable breeding ground for different styles of music over the years, New Orleans' regarded artistic reputation was established by its jazz movement which began around the turn of the 20th Century. However, it was its equally influential rhythm and blues scene, pioneered by legends like Fats Domino, which inadvertently helped shape not only what Black Sabbath went on to amplify to a deafening metallic roar a couple of decades later but also the metal musicians of the Crescent City who followed.

Most noticeably, NOLA blues musician Dr. John's fondness for drum beats that lagged behind the guitars really engrained itself in impressionable young NOLA musicians like Jimmy Bower, Philip H. Anselmo, Kirk Windstein, Mike Williams and Joey LaCaze. As a result, the implementation of this technique effectively gave their metal its signature sludgy crawl, indicative of the slow approach to life in New Orleans because of its stifling climate. Like the homogenous blues of their eclectic hometown, Black Sabbath's music – including the band's post-Ozzy output – was equally bred into Louisiana's metal-lifers from a young age. In turn, their bands – Down, Crowbar and Eyehategod – were all massively influenced at their various formations by the sativa-smoke riffs of Sabbath's 'Sweet Leaf', the paranoia and foreboding of the title track off that world-changing debut, the narcotic excess of 'Snowblind', the social commentary and impending doom at the core of 'Children of the Grave' and 'Iron Man' and so on.

These three bands then took what Sabbath as well as Saint Vitus, Trouble, Pentagram, Witchfinder General et al did before them and NOLA-ized it by instilling the intensity of the claustrophobic heat of their swampy surrounds and the hardcore punk, blues and Southern rock music of their childhoods (Black Flag, Discharge, Dr. John, The Allman Brothers, Led Zeppelin, Lynyrd Skynyrd...) But also – and more importantly – their individual fears, flaws, demons and dependencies. The results of this collision of complimentary styles and the every-day realism at the pith of each bands' lyrics were massive, as along with The Melvins out of Seattle, their unique amalgam created what is now known as sludge metal.

By the end of the 1990s, Down's supergroup status (the band comprised of members of Pantera, Crowbar, Eyehategod and Corrosion of Conformity) had played a huge role in trusting the sludge metal of the Bayou into the mainstream's limelight, even though Exhorder's swamp-thrash debut Slaughter In The Vatican (1990) followed by Eyehategod's first release, In The Name Of Suffering (1992), were the first to really run rampant throughout the underground metal scene. The then side-project of Pantera frontman Phil Anselmo caused quite a stir with their three-song demo before going on to release of the now-classic NOLA album in 1995. The huge draw of Anselmo's name at that time – not to mention the quality of NOLA's platinum selling jams like the punishing 'Temptations Wings', the Skynyrdisms of 'Stone The Crow' and 'Bury Me In Smoke''s doom dogma – brought greater exposure to the bands of his formidable Down brothers.

North Carolina's Corrosion of Conformity were already a big deal in underground circles because of how influential they were in bringing hardcore, punk and metal factions together during the late 80s with crossover milestones like Animosity (1985). As time passed and members changed, including the addition of guitarist Pepper Keenan in 1990 (who eventually relocated to New Orleans), Corrosion of Conformity shifted their focus away from hardcore to fully embrace Sabbath, Skynyrd and Thin Lizzy, culminating in their best album of that era –the raucous rawk of 1994's Deliverance. Alongside Corrosion of Conformity stood the straightforward riff-heft of guitarist Kirk Windstein's Crowbar, the most underrated band out of all the Down members' individual groups, whose earnest music came loaded with skull-crushing weight. While lurking in shadows of New Orleans were Down drummer Jimmy Bower's Eyehategod, the most seething, feral and nihilistic entity of the lot. A band that, over the years, has played an essential part in extreme metal's evolution, with the likes of Noothgrush, Lord Mantis, Dragged Into Sunlight, and the much missed Iron Monkey being a few of the miscreants that have feasted upon the filth Eyehategod polluted us with on Take As Needed For Pain (1993) and the equally carcinogenic, Dopesick (1995).

Just like Black Sabbath, lifelong friendships formed the basis of the metal bands of New Orleans and their kinship fed their artistic successes. As well as the creative highs, the relationships of members of Down, Crowbar and Eyehategod have gone through the usual human troubles as well as crippling drug addictions, which have made metal's headlines in the cases of Anselmo and Williams, while Windstein's battles with the bottle have also been well-documented. However, the murder of Pantera guitar master Dimebag Darrell, which sent a seismic shockwave across the scene that is still felt today, and the life-changing impact of Hurricane Katrina in 2005 proved to be the reality check needed for these musicians to finally get clean. And while different members have passed through each band, whether by choice (bassist Rex Brown and guitarist Kirk Windstein's departures from Down in recent years) or because of fate's cruel hand (the unfortunate passing of Eyehategod drummer Joey LaCaze in 2013), the roots of Down, Crowbar and Eyehategod remain firmly in the ground of New Orleans despite the preceding negativity.

This May, the stars aligned over Louisiana as these three forefathers of NOLA metal released new material, further confirming that these veteran acts won't rest and that the music of their youth is still an inspiration decades later.

2012's Down IV - Part I, or The Purple EP as it became known, was the first Down recording with Pat Bruders (Goatwhore, Crowbar) on bass after former Pantera four-stringer Rex Brown left the band in 2011. As it happened, it was also the last Down recording with Windstein on guitar, as he left to focus on Crowbar. Their second EP of their recent series, Down IV - Part II, introduces guitarist Bobby Landgraf, a long-time friend and stage manager of the band, who, judging by the strength of the doom riffs he trades with Keenan, has slotted naturally into Down's line-up. Consequentially, Down's worship of the Sabbathian sermons of yesteryear is stronger than ever before. This is explicitly so on track three, the cease-and-desist baiting 'Conjure': Anselmo does his best Ozzy impression with lines like, "Snort the powder of life..." and the soothsaying chorus of "Beware the conjure!", while the songwriting is prototypical Sabbath in terms of its structure, Iommic riffs and the signature tempo jolt three-thirds the way through.

Such a stance, though typical of Down's oeuvre since their demo, comes as a surprise because the band maintained at the beginning of this EP series that each instalment would differ from the last, with acoustic and experimental Down music mentioned publicly. But from the minute the bullish 'Steeple' (a song that sounds like Mastodon gone doom metal) opens Part II to 'Bacchanalia''s pysch-dyed acoustic-end, you're made aware that there are little or no risks taken by Down this time 'round. This may disappoint those looking for the band to try something different rather than their staple brawling blues licks and hulking grooves, although these six songs do connect quicker than those on their previous EP.

The reason for the lack of adventure may stem from the reality in which the band found themselves a riff-writer down and instead of trying something different, they thought best to jam heavy with Landgraf to see to if their collective chemistry for creating metal remained intact. 'We Knew Him Well' and 'Sufferer's Years', in particular, cement the NOLA sound characterised by Down in place, with monstrous central riffs driving both songs onward. While closer 'Bacchanalia' pays homage to Be Forewarned-era Pentagram with Victor Griffinesque slabs of riffs and Anselmo's reliance on his black book of doom singers to reinterpret Bobby Liebling's vocal mannerisms in his own gruff and dominant style.

Again, none of this is new for Down, but the songwriting is primed and potent and therefore each of the six songs should satiate the demand Down fans have for new music from the NOLA originals. However, experimentation and deviation from the norm was anticipated and hoped for, and with four more EPs in the pipeline, they may finally step outside their tar-covered hot-box, as the end of 'Bacchanalia' subtly suggests.

Like Down, when a new Crowbar album nears its release you can usually guess what's going to be dished up by Windstein and company. Such predictability, although a dirty word at times, isn't always a bad thing, as Motörhead and AC/DC fans will attest. Because while experimentation may lead to boundary breaking music, we do still need the bands that find their niche and lodge their feet in the ground to continue to create around an immovable base while placing greater emphasis on sacred song-craft. Unlike Down and Eyehategod however, Crowbar have never released an album that you would label as a world-beating "classic", though 1993's Crowbar and 1998's Odd Fellows Rest do stake their claim as two of the best metal albums to come out of the Big Easy.

The four-piece band's latest album (tenth studio recording overall) in an existence which has spanned two decades, Symmetry In Black, really benefits from Windstein's full, undivided attention. On their last album Sever The Wicked Hand (2011), Windstein had spread himself too thin by trying to split his time between Crowbar and Down as well as Kingdom of Sorrow, the band he formed in 2005 with Hatebreed's Jamey Jasta. You could hear how stretched he was in the dipped quality of the music on Sever The Wicked Hand, and that's one noticeable difference on Symmetry In Black: Windstein's full dedication to this Crowbar album has produced stronger songs from front to back and a more cohesive and better paced record overall.

The time spent on song-craft has made sure each song has its own individuality, even though the individuality is still a variation on a time-tested theme. The first four songs in particular all stick to verse/chorus structures with Windstein either screaming the verses then singing the chorus ('The Taste of Dying') or vice versa (the Alice in Chains-inspired 'Symmetry In White') while the music churns beneath, groove-orientated and mid-paced. Each song gives us a glimpse of the inner working of a troubled man who wants to better himself, all set to the soundtrack of catchy, chugging sludge riffs and lumbering rhythms.

During the opening gut-check of 'Walk With Knowledge Wisely', Windstein lets us straight inside his head: “Walk with knowledge wisely. You don't have to die. Put an end to what poisons you.” He shouts this more life-hardened than ever before but devoid of sounding sanctimonious. In fact, the lyrics of the entire record read like a glimpse into Windstein's personal journal rather than a misguided attempt to preach at the listener: “Into freedom I lead you, know I'm not the enemy. I can teach the blind to see, just believe and follow me. This becomes a legacy.” Taken from 'Teach The Blind To See', normally this kind of lyric would even make a Creed fan's arsehole wince, but Windstein's authenticity and introspective bent turns it into a battle-cry – a sign that working with hardcore figurehead Jasta has influenced Winstein as much as it has Jasta.

Elsewhere, the positioning of 'Ageless Decay' is essential to the flow of Symmetry In Black; its hardcore punk heritage highlights that Greg Ginn was as much an influence to NOLA metal as Tony Iommi. This song gives the album a timely injection of pace, repeated later with the double-bass propelled 'Symbolic Suicide'. On the other hand, 'Amaranthine' acts as a gentle reprieve, a track dedicated to Windstein's wife (“I'll never walk alone”). While 'The Foreboding' chases a lineage back to Butler's lyrics for 'Black Sabbath' and interestingly Anselmo's own decrees on the aforementioned 'Conjure': "I'm looking straight into the future, right into its eyes. And what I'm looking at is evil..."

With Symmetry In Black, Crowbar have delivered a statement of intent for the future of this NOLA band; the signs were there from the moment they presented the artwork of the fleur-de-lis centred on a black backdrop. Revitalised and more determined than ever, never has the impression that the best of Crowbar has yet to come been so vocal and obvious as it is in 2014.

As much as Crowbar's cover art is an assertion of what we can expect to find within, eponymously titling an album is as much a declaration of definitiveness as it was when Sabbath dropped their self-titled debut on an unsuspecting world in 1970. Following this tradition are Eyehategod, who now return with their first album in fourteen years. And like Symmetry In Black, Eyehategod is also a statement of intent (a greater one, in fact), an album created by a band that more now than ever need to keep their unity in place.

After having their world rocked by the devastation Hurricane Katrina brought in 2005, the death of founding member Joey LaCaze last year as a result of complications from asthma was another knee-buckling blow for the band. LaCaze's drumming was always on the brink of careening off the rails because of his sharp tempo changes and tendency to play in and out of the riffs, and while his interplay with guitarists Bower and Brian Patton cannot be underestimated, it was his relationship with Williams' timely outpouring of poetic bile which gave Eyehategod its chaotic signature style. It is some consolation for fans at least that LaCaze got to lay down his drum parts for Eyehategod before he was sadly taken from us and he makes his mark immediately with the incendiary 'Agitation! Propaganda!' The broiling atmosphere is whipped up by a flurry of D-beats, shifting chords and Williams' distorted screams which re-introduce Eyehategod like a flaming boot to the throat before the curb-stomp of a sludge riff quells the fire.

From here, Eyehategod are relentless, though they rarely choose to work with fast tempos again. The brilliantly titled 'Trying To Crack The Hard Dollar' is methodically constructed, swinging one minute and chucking feverishly through streams of feedback the next. This template is used to even greater effect during 'Parish Motel Sickness' as the band take Master Of Reality as starting point and drag it through the scummy gutters of NOLA, sounding both musically and vocally as if the last fourteen years didn't happen. 'Quitter's Offensive' and 'Nobody Told Me' also shuffle and slash pugnaciously without forgetting the importance of groove; albeit grooves that buck wildly because of LaCaze's eagerness to twist, contort and re-invent. The drummer's rhythmic restlessness is further presented on 'Framed To The Wall': the ascending and descending blues scales are fragmented and reconstructed through a hardcore punk aesthetic, the song covering plenty of ground in the process.

This is the wretched beauty of Eyehategod's music: While Down and Crowbar are both traditionalists at heart, Eyehategod are the innovators of NOLA metal. Since their inception, they have been unafraid to take their inspirations mentioned at the outset of this piece and mutate them through the use of high-impact squalls of noise-riddled sludge riffs; non-linear rhythms, tireless in their thirst to influence the direction of the guitars; and vicious vocals that refuse to thread a beaten path and instead take a maverick approach, independent yet complimentary to the overall scheme of things in terms of delivery and content – best highlighted here by 'Nobody Told Me', 'Flags and Cities Bound' and 'Medicine Noose'.

Besides the musical similarities and differences of Down, Crowbar and Eyehategod, these bands share the same unbreakable spirit, which is truly brought into focus in the case of Eyehategod's self-titled proclamation of power in times of grief. It is a kind of resiliency that flies in the face of the trials that human nature and nature itself can drop before us without a warning. As the news headlines since 2005 have proven, the natives of New Orleans are made of sterner stuff, rebuilding their lives after physical, mental and financial collapse. These three bands have also proven their resilience as well as their imperfections and innate predilection to make mistakes over the years, whether during good or bad times. Hell, Williams, who has been homeless in the past and has also served time in prison while coming off heroin, acknowledges such failings during album highlight 'Parish Motel Sickness', when he screams repeatedly: "Sometimes I'm stuck together, sometimes I come unglued."

We can all relate to this simple but honest line - the most audible lyric of the entire album, and probably intentionally so. It also sums up the personal and professional past of each member of Down, Crowbar and Eyehategod. Yet in spite of all that's gone before, the metal music of New Orleans lives on. In fact not only does it live on, as the three albums discussed above demonstrates, it thrives because of each band's unbreakable spirit strengthened by a pure love of their own art and the music of their youth. It's this spirit which unites Down, Eyehategod, Crowbar and their ilk, and in turn it is what continues to makes us, the listener, palpably feel a part of the metal music of New Orleans, Louisiana.