Technical death metal and progressive death metal are subgenres of Death Metal that infuse the (in)famous assaulting musical brutality of the genre with the technicality and elaborate musical structures of Progressive Metal. The songs tend to be very complex, and often include influences from other genres, such as jazz or classical music; the result is a highly cerebral musical style that rewards close and repeated listening, without surrendering the unrelenting musical aggression Death Metal is known for.
There is, or can be, a difference between "technical death metal" and "progressive death metal", though many artists fit both descriptions or oscillate between. While both are undeniably musically sophisticated and extremely brutal, tech death bands tend to come across as much more intense, often performing their complex compositions with blinding speed and pounding aggression, or in a manner that emphasises the virtuosic skill and precision of the performances. Technical death metal can thus sometimes have a somewhat machine-like, "triggered" sound, with instruments starting and stopping suddenly or irregularly, playing precisely calculated riffs or patterns which shift frequently and sometimes seemingly at random, only to form part of a larger motif or series of progressions which become apparent upon close listening.
"Progressive death metal", on the other hand, tempers the conventional "death metal" repertoire of elements with jazzy breakdowns, melodic refrains, unusual (for death metal) instrumentation and vocalisation, or slower tempi, and generally draws liberally from diverse musical traditions to create elaborate, multilayered sounds that evolve across lengthy and eclectic albums. Progressive death metal thus tends to be more diverse or less identical-sounding, in that while tech death bands commonly draw inspiration from other musical forms, progressive death metal bands often do so multiply within a single song or album, and though demonstrably capable of the sort of chops-intensive wizardry found in tech death, prog death bands often forego these displays in favour of allowing their compositions time to breathe via greater repetition, subtler permutation, and more extensive progression.
Thus the distinction could be argued to be that technical death metal prides itself on instrumental skill and experimentation, while progressive death metal prides itself on compositional exploration and originality. A quicker way to explain the difference to a metalhead would be this:
Deserving special attention are Death, not only for inventing Death Metal as a whole, but for subsequently kickstarting both prog and tech with their 1991 album Human, which stood head-and-shoulders above contemporaneous releases in terms of the proficiency and originality of its songcraft and production, with seriously insightful lyrics accompanying inventive chords through inspired and memorable songwriting. It and all subsequent Death albums are considered standard-setting classics, with Humannote Lack Of Comprehension and Individual Thought Patternsnote Trapped In A Corner cleaving more closely to technical death metal and Symbolicnote Crystal Mountain and The Sound of Perseverancenote The Flesh And The Power It Holds closer to progressive death metal to the contemporary ear.
Further bands that are generally classified as technical/progressive death metal (exact subgenre noted by their name) include:
Wormed (brutal tech with deathgrind influence; debatably prog-ish on their latest release, Exodromos)
Tropes that apply to prog/tech death:
A God Am I: Tech death acts, especially those who write fantasy-based lyrics, are particularly infamous for invoking this trope. The lyrical implementation can range from something as relatively tame as having control over the future to a straight-up insatiable desire to destroy everyone and everything. Often written in Purple Prose for maximum effect.
Though it may be argued that within the generic context these individuals and others ought to count as Type D examples, rather than strictly Type A. Because both prog and tech death place substantial emphasis on writing interesting and challenging parts for all instruments, bassists in the genre are, moreso than in other rock or metal genres, considered to be integral if not central to the band's sound, and thus cut far larger figures within the consciousness of fans, and are simply unlikely to be overlooked, especially if they are particularly skilled.
The abundance and popularity of bass solos, or duelling solos in which the bassist and the lead guitarist trade off against one another, probably doesn't hurt either.
Lyrical Dissonance - Despite being death metal, lyrics range about evenly from the traditional DeathyGorn to philosophy, social commentary, speculative fiction, spirituality or the occult, and even comedy.
Neoclassical Punk Zydeco Rockabilly - Mostly prog death, which often aims to produce truly excellent death metal by combining it with elements of just about every other excellent form of music in existence.
The Scrappy: The genre has been steadily becoming this in the eyes of purists due to the amount of bands going "tech" and changing their lyrical approach to vaguely philosophical/metaphysical Purple Prose-filled rambling about how powerful and almighty the lyricist/band is, particularly deathcore acts. The fact that some of these acts have apparently been falling flat live, implying that a lot of their supposed technicality has been achieved through studio trickery, also hasn't helped.
For that matter, some of the less structured, more "weedly" acts have become particularly hated for different reasons, with the prevailing sentiment being that they're aimless bedroom shredder music with no focus on actual song structure that aims solely to show how fast the guitarists can sweep and how many needless gravity blasts the drummers can cram in, with Brain Drill, Viraemia, and Slaughterbox being held up as particularly obnoxious examples, as well as Rings of Saturn and Beneath the Massacre for combining this sound with deathcore.