Pentium 4

Pentium 4

Produced	From 2000 to 2008
Max. CPU clock rate	1.3 GHz to 3.8 GHz
FSB speeds	400 MT/s to 1066 MT/s
Instruction set	x86 (i386), x86-64, MMX, SSE, SSE2, SSE3
Microarchitecture	NetBurst
Transistors	42M 180 nm 55M 130 nm 169M 130 nm (P4EE) 125M 90 nm 188M 65 nm
Socket(s)	Socket 423 Socket 478 LGA 775
Predecessor	Pentium III
Successor	Pentium D

Pentium 4 is a line of single-core central processing units (CPUs) for desktops, laptops and entry-level servers introduced by Intel on November 20, 2000^[1] and shipped through August 8, 2008.^[2] They had a seventh-generation x86 (32-bit) microarchitecture, called NetBurst, which was the company's first all-new design since the introduction of the P6 microarchitecture of the Pentium Pro CPUs in 1995. NetBurst differed from P6 (Pentium III, II, etc.) by featuring a very deep instruction pipeline to achieve very high clock speeds. Intel claimed that NetBurst would allow clock speeds of up to 10 GHz in future chips; however, severe problems with heat dissipation (especially with the Prescott Pentium 4) limited CPU clock speeds to a much lower 3.8 GHz.^[3]

In 2004, the initial 32-bit x86 instruction set of the Pentium 4 microprocessors was extended by the 64-bit x86-64 set.

The first Pentium 4 cores, codenamed Willamette, were clocked from 1.3 GHz to 2 GHz. They were released on November 20, 2000, using the Socket 423 system. Notable with the introduction of the Pentium 4 was the 400 MT/s FSB. It actually operated at 100 MHz, but the FSB was quad-pumped, meaning that the maximal transfer rate was four times the base clock of the bus, so it was marketed to run at 400 MHz. The AMD Athlon's double-pumped FSB was running at 100 or 133 MHz (200 or 266 MT/s) at that time.

Pentium 4 CPUs introduced the SSE2 and, in the Prescott-based Pentium 4s, SSE3 instruction sets to accelerate calculations, transactions, media processing, 3D graphics, and games. Later versions featured Hyper-Threading Technology (HTT), a feature to make one physical CPU work as two logical CPUs. Intel also marketed a version of their low-end Celeron processors based on the NetBurst microarchitecture (often referred to as Celeron 4), and a high-end derivative, Xeon, intended for multiprocessor servers and workstations. In 2005, the Pentium 4 was complemented by the Pentium D and Pentium Extreme Edition dual-core CPUs.

Microarchitecture

In benchmark evaluations, the advantages of the NetBurst microarchitecture were unclear. With carefully optimized application code, the first Pentium 4s outperformed Intel's fastest Pentium III (clocked at 1.13 GHz at the time), as expected. But in legacy applications with many branching or x87 floating-point instructions, the Pentium 4 would merely match or run more slowly than its predecessor. Its main handicap was a shared unidirectional bus. Furthermore, the NetBurst microarchitecture consumed more power and emitted more heat than any previous Intel or AMD microarchitectures.

As a result, the Pentium 4's introduction was met with mixed reviews: Developers disliked the Pentium 4, as it posed a new set of code optimization rules. For example, in mathematical applications, AMD's lower-clocked Athlon (the fastest-clocked model was clocked at 1.2 GHz at the time) easily outperformed the Pentium 4, which would only catch up if software was re-compiled with SSE2 support. Tom Yager of Infoworld magazine called it "the fastest CPU - for programs that fit entirely in cache". Computer-savvy buyers avoided Pentium 4 PCs due to their price premium, questionable benefit, and initial restriction to Rambus RAM. In terms of product marketing, the Pentium 4's singular emphasis on clock frequency (above all else) made it a marketer's dream. The result of this was that the NetBurst microarchitecture was often referred to as a marchitecture by various computing websites and publications during the life of the Pentium 4. It was also called "NetBust," a term popular with reviewers who reflected negatively upon the processor's performance.

The two classical metrics of CPU performance are IPC (instructions per cycle) and clock speed. While IPC is difficult to quantify due to dependence on the benchmark application's instruction mix, clock speed is a simple measurement yielding a single absolute number. Unsophisticated buyers would simply consider the processor with the highest clock speed to be the best product, and the Pentium 4 had the fastest clock speed. Because AMD's processors had slower clock speeds, it countered Intel's marketing advantage with the "megahertz myth" campaign. AMD product marketing used a "PR-rating" system, which assigned a merit value based on relative performance to a baseline machine.

At the launch of the Pentium 4, Intel stated that NetBurst-based processors were expected to scale to 10 GHz after several fabrication process generations. However, the clock speed of processors using the NetBurst microarchitecture reached a maximum of 3.8 GHz. Intel had not anticipated a rapid upward scaling of transistor power leakage that began to occur as the die reached the 90 nm lithography and smaller. This new power leakage phenomenon, along with the standard thermal output, created cooling and clock scaling problems as clock speeds increased. Reacting to these unexpected obstacles, Intel attempted several core redesigns ("Prescott" most notably) and explored new manufacturing technologies, such as using multiple cores, increasing FSB speeds, increasing the cache size, and using a longer instruction pipeline along with higher clock speeds. These solutions failed, and from 2003 to 2005, Intel shifted development away from NetBurst to focus on the cooler-running Pentium M microarchitecture. On January 5, 2006, Intel launched the Core processors, which put greater emphasis on energy efficiency and performance per clock cycle. The final NetBurst-derived products were released in 2007, with all subsequent product families switching exclusively to the Core microarchitecture.

Processor cores

Intel Pentium 4 processor family

Desktop			Laptop
Code-named	Core	Date released	Code-named	Core	Date released
Willamette Northwood Prescott	180 nm 130 nm 90 nm	Nov 2000 Jan 2002 Mar 2004	Northwood	130 nm	Jun 2003
			Northwood Pentium 4-M	130 nm	Apr 2002
Hyper-threading (HT)
Northwood Prescott Prescott 2M Cedar Mill	130 nm 90 nm 90 nm 65 nm	May 2003 Feb 2004 Feb 2005 Jan 2006	Northwood Prescott	130 nm 90 nm	Sep 2003 Jun 2004
Gallatin XE Prescott 2M XE	130 nm 90 nm	Sep 2003 Feb 2005
List of Intel Pentium 4 microprocessors

Pentium 4 processors have an integrated heat spreader (IHS) that prevents the die from accidentally being damaged when mounting and unmounting cooling solutions. Prior to the IHS, a CPU shim was sometimes used by people worried about damaging the core. Overclockers sometimes removed the IHS from Socket 423 and Socket 478 chips to allow for more direct heat transfer. On processors using the Socket LGA 775 (Socket T) interface, the IHS is directly soldered to the die or dies, making it difficult to remove.

Willamette

Willamette, the project codename for the first NetBurst microarchitecture implementation, experienced long delays in the completion of its design process. The project was started in 1998, when Intel saw the Pentium II as their permanent line. At that time, the Willamette core was expected to operate at frequencies up to about 1 GHz. However, the Pentium III was released while Willamette was still being finished. Due to the radical differences between the P6 and NetBurst microarchitectures, Intel could not market Willamette as a Pentium III, so it was marketed as the Pentium 4.

On November 20, 2000, Intel released the Willamette-based Pentium 4 clocked at 1.4 and 1.5 GHz. Most industry experts regarded the initial release as a stopgap product, introduced before it was truly ready. According to these experts, the Pentium 4 was released because the competing Thunderbird-based AMD Athlon was outperforming the aging Pentium III, and further improvements to the Pentium III were not yet possible. This Pentium 4 was produced using a 180 nm process and initially used Socket 423 (also called socket W, for "Willamette"), with later revisions moving to Socket 478 (socket N, for "Northwood"). These variants were identified by the Intel product codes 80528 and 80531 respectively.

On the test bench, the Willamette was somewhat disappointing to analysts in that not only was it unable to outperform the Athlon and the highest-clocked Pentium IIIs in all testing situations, but it was not superior to the budget segment's AMD Duron.^[4] Although introduced at prices of $644 (1.4 GHz) and $819 (1.5 GHz) for 1000 quantities to OEM PC manufacturers (prices for models for the consumer market varied by retailer), it sold at a modest but respectable rate, handicapped somewhat by the requirement for relatively fast yet expensive Rambus Dynamic RAM (RDRAM). The Pentium III remained Intel's top selling processor line, with the Athlon also selling slightly better than the Pentium 4. While Intel bundled two RDRAM modules with each boxed Pentium 4, it did not facilitate Pentium 4 sales and was not considered a true solution by many.

In January 2001, a still slower 1.3 GHz model was added to the range, but over the next twelve months, Intel gradually started reducing AMD's leadership in performance. In April 2001 a 1.7 GHz Pentium 4 was launched, the first model to provide performance clearly superior to the old Pentium III. July saw 1.6 and 1.8 GHz models and in August 2001, Intel released 1.9 and 2 GHz Pentium 4s. In the same month, they released the 845 chipset that supported much cheaper PC133 SDRAM instead of RDRAM.^[5] The fact that SDRAM was so much cheaper caused the Pentium 4's sales to grow considerably.^[5] The new chipset allowed the Pentium 4 to quickly replace the Pentium III, becoming the top-selling mainstream processor on the market.

The Willamette code name is derived from the Willamette Valley region of Oregon, where a large number of Intel's manufacturing facilities are located.

Northwood

In January 2002 Intel released Pentium 4s with a new core code named "Northwood" at speeds of 1.6 GHz, 1.8 GHz, 2 GHz and 2.2 GHz.^[6][7] Northwood (product code 80532) combined an increase in the L2 cache size from 256 KB to 512 KB (increasing the transistor count from 42 million to 55 million) with a transition to a new 130 nm fabrication process.^[7] Making the processor out of smaller transistors means that it can run at higher clock speeds and produce less heat. In the same month boards utilizing the 845 chipset were released with enabled support for DDR SDRAM which provided double the bandwidth of PC133 SDRAM, and alleviated the associated high costs of using Rambus RDRAM for maximal performance with Pentium 4.

A 2.4 GHz Pentium 4 was released on April 2, 2002, and the bus speed increased from 400 MT/s to 533 MT/s (133 MHz physical clock) for the 2.26 GHz, 2.4 GHz, and 2.53 GHz models in May, 2.66 GHz and 2.8 GHz models in August, and 3.06 GHz model in November. With Northwood, the Pentium 4 came of age. The battle for performance leadership remained competitive (as AMD introduced faster versions of the Athlon XP) but most observers agreed that the fastest-clocked Northwood-based Pentium 4 was usually ahead of its rival. This was particularly so in mid-2002, when AMD's changeover to its 130 nm production process did not help the initial "Thoroughbred A" revision Athlon XP CPUs to clock high enough to overcome the advantages of Northwood in the 2.4 to 2.8 GHz range.^[8]

The 3.06 GHz Pentium 4 enabled Hyper-Threading Technology that was first supported in Foster-based Xeons. This began the convention of virtual processors (or virtual cores) under x86 by enabling multiple threads to be run at the same time on the same physical processor. By shuffling two (ideally differing) program instructions to simultaneously execute through a single physical processor core, the goal is to best utilize processor resources that would have otherwise been unused from the traditional approach of having these single instructions wait for each other to execute singularly through the core. This initial 3.06 GHz 533FSB Pentium 4 Hyper-Threading enabled processor was known as Pentium 4 HT and was introduced to mass market by Gateway in November 2002.

On April 14, 2003, Intel officially launched the new Pentium 4 HT processor. This processor used an 800 MT/s FSB (200 MHz physical clock), was clocked at 3 GHz, and had Hyper-Threading Technology (which is what the HT moniker represents).^[9] This was meant to help the Pentium 4 better compete with AMD's Opteron line of processors. The server-oriented Opteron initially did not share a common socket with AMD's desktop processor line (Socket A). Because of this, motherboard manufacturers did not initially build motherboards with AGP for Opterons. As AGP was the primary graphics expansion port for desktop use, this oversight prevented the Opteron from encroaching from the server market and threatening the Pentium 4 desktop market. Meanwhile, with the launch of the Athlon XP 3200+ in AMD's desktop line, AMD increased the Athlon XP's FSB speed from 333 MT/s to 400 MT/s, but it was not enough to hold off the new 3 GHz Pentium 4 HT.^[10] The Pentium 4 HT's increase to a 200 MHz quad-pumped bus (200x4=800Mhz effective) greatly helped to satisfy the bandwidth requirements the Netburst architecture desired for reaching optimal performance. While the Athlon XP architecture was less dependent on bandwidth, the bandwidth numbers reached by Intel were well out of range for the Athlon's EV6 bus. Hypothetically, EV6 could have achieved the same bandwidth numbers, but only at speeds unreachable at the time. Intel's higher bandwidth proved useful in benchmarks for streaming operations, and Intel marketing wisely capitalized on this as a tangible improvement over AMD's desktop processors. Northwood 2.4 GHz, 2.6 GHz and 2.8 GHz variants were released on May 21, 2003. A 3.2 GHz variant was launched on June 23, 2003 and the final 3.4 GHz version arrived on February 2, 2004.

Overclocking early stepping Northwood cores yielded a startling phenomenon. While core voltage approaching 1.7 V and above would often allow substantial additional gains in overclocking headroom, the processor would slowly (over several months or even weeks) become more unstable over time with a degradation in maximum stable clock speed before dying and becoming totally unusable. This became known as Sudden Northwood Death Syndrome (SNDS), which is caused by electromigration.^[11]

Pentium 4-M

Also based on the Northwood core, the Mobile Intel Pentium 4 Processor - M^[12] was released on April 23, 2002 and included Intel's SpeedStep and Deeper Sleep technologies. Intel's naming conventions made it difficult at the time of the processor's release to identify the processor model. There was the Pentium III mobile chip, the Mobile Pentium 4-M, the Mobile Pentium 4, and then just the Pentium M which itself was based on the Pentium III and significantly faster than the former three. Its TDP is about 35 watts in most applications. This lowered power consumption was due to lowered core voltage, and other features mentioned previously.

Unlike the desktop Pentium 4, the Pentium 4-M did not feature an integrated heat spreader (IHS), since it operates at a lower voltage. The lower voltage means lower power consumption, and in turn less heat. However, according to Intel specifications, the Pentium 4-M had a maximum thermal junction temperature rating of 100 degrees C, approximately 40 degrees higher than the desktop Pentium 4.

Mobile Pentium 4

The Mobile Intel Pentium 4 Processor^[13] was released to address the problem of putting a full desktop Pentium 4 processor into a laptop, which some manufacturers were doing. The Mobile Pentium 4 used a 533 MT/s FSB, following the desktop Pentium 4's evolution. Oddly, increasing the bus speed by 133 MT/s (33 MHz) caused a massive increase in TDPs, as mobile Pentium 4 processors emitted 59.8–70 W of heat, with the Hyper-Threading variants emitting 66.1–88 W. This allowed the mobile Pentium 4 to bridge the gap between the desktop Pentium 4 (up to 115 W TDP), and the Pentium 4-M (up to 35 W TDP).

Gallatin (Extreme Edition)

In September 2003, at the Intel Developer Forum, the Pentium 4 Extreme Edition (P4EE) was announced, just over a week before the launch of Athlon 64 and Athlon 64 FX. The design was mostly identical to Pentium 4 (to the extent that it would run in the same motherboards), but differed by an added 2 MB of level 3 cache. It shared the same Gallatin core as the Xeon MP, though in a Socket 478 form factor (as opposed to Socket 603 for the Xeon MP) and with an 800 MT/s bus, twice as fast as that of the Xeon MP.

While Intel maintained that the Extreme Edition was aimed at gamers, critics viewed it as an attempt to steal the Athlon 64's launch thunder, nicknaming it the "Emergency Edition". With a price tag of $999, it was also referred to as the "Expensive Edition" or "Extremely Expensive".

The added cache generally resulted in a noticeable performance increase in most processor intensive applications. Multimedia encoding and certain games benefited the most, with the Extreme Edition outperforming the Pentium 4, and even the two Athlon 64 variants, although the lower price and more balanced performance of the Athlon 64 (particularly the non-FX version) led to it usually being seen as the better value proposition. Nonetheless, the Extreme Edition did achieve Intel's apparent aim, which was to prevent AMD from being the performance champion with the new Athlon 64, which was winning every single major benchmark over the existing Pentium 4s.

In January 2004 a 3.4 GHz version was released for Socket 478, and in Summer 2004 the CPU was released using the new Socket 775. A slight performance increase was achieved in late 2004 by increasing the bus speed from 800 MT/s to 1066 MT/s, resulting in a 3.46 GHz Pentium 4 Extreme Edition. By most metrics, this was on a per-clock basis the fastest single-core NetBurst processor that was ever produced, even outperforming many of its successor chips (not counting the dual-core Pentium D). Afterwards, the Pentium 4 Extreme Edition was migrated to the Prescott core. The new 3.73 GHz Extreme Edition had the same features as a 6x0-sequence Prescott 2M, but with a 1066 MT/s bus. In practice however, the 3.73 GHz Pentium 4 Extreme Edition almost always proved to be slower than the 3.46 GHz Pentium 4 Extreme Edition, which is most likely due to the lack of an L3 cache and the longer instruction pipeline. The only advantage the 3.73 GHz Pentium 4 Extreme Edition had over the 3.46 GHz Pentium 4 Extreme Edition was the ability to run 64-bit applications since all Gallatin-based Pentium 4 Extreme Edition processors lacked the Intel 64 instruction set.

Although never a particularly good seller, especially since it was released in a time when AMD were asserting near total dominance in the processor performance race, the Pentium 4 Extreme Edition established a new position within Intel's product line, that of an enthusiast oriented chip with the highest-end specifications offered by Intel chips, along with unlocked multipliers to allow for easier overclocking. In this role it has since been succeeded by the Pentium Extreme Edition (The Extreme version of the dual-core Pentium D), the Core 2 Extreme, the Core i7 and most recently, the Core i9.

Prescott

On February 1, 2004, Intel introduced a new core codenamed "Prescott". The core used the 90 nm process for the first time, which one analyst described as "a major reworking of the Pentium 4's microarchitecture."^[14] Despite this overhaul, the performance gains were inconsistent. Some programs benefited from Prescott's doubled cache and SSE3 instructions, whereas others were harmed by its longer pipeline. The Prescott's microarchitecture allowed slightly higher clock speeds, but not nearly as high as Intel had anticipated. The fastest mass-produced Prescott-based Pentium 4s were clocked at 3.8 GHz. While Northwood ultimately achieved clock speeds 70% higher than Willamette, Prescott scaled 12% beyond Northwood. Prescott's inability to achieve greater clock speeds was attributed to the very high power consumption and heat output of the processor. This led to the processor receiving the nickname "PresHot" on forums. In fact, Prescott's power and heat characteristics were only slightly higher than those of Northwood of the same speed and nearly equal to the Gallatin-based Extreme Editions, but since those processors had already been operating near the limits of what was considered thermally acceptable, this still posed a major issue.^[15]

The "Prescott" Pentium 4 contains 125 million transistors and has a die area of 112 mm².^[16][17] It was fabricated in a 90 nm process with seven levels of copper interconnect.^[17] The process has features such as strained silicon transistors and Low-K carbon-doped silicon oxide (CDO) dielectric, which is also known as organosilicate glass (OSG).^[17] The Prescott was first fabricated at the D1C development fab and was later moved to F11X production fab.^[17]

Originally, Intel released two Prescott lines: the E-series, with an 800 MT/s FSB and Hyper-Threading support, and the low-end A-series, with a 533 MT/s FSB and Hyper-Threading disabled. Intel eventually added XD Bit (eXecute Disable) and Intel 64 functionality to Prescott.

LGA 775 Prescott uses a rating system, labeling them as the 5xx series (Celeron Ds are the 3xx series, while Pentium Ms are the 7xx series). The LGA 775 version of the E-series uses model numbers 5x0 (520-560), and the LGA 775 version of the A-series uses model numbers 5x5 and 5x9 (505-519). The fastest, the 570J and 571, is clocked at 3.8 GHz. Plans to mass-produce a 4 GHz Pentium 4 were cancelled by Intel in favor of dual core processors, although some European retailers claimed to be selling a Pentium 4 580, clocked at 4 GHz.

The 5x0J series (and its low-end equivalent, the 5x5J and 5x9J series) introduced the XD Bit a.k.a. eXecute Disabled Bit^[18] to Intel's line of processors. This technology, introduced to the x86 line by AMD and called NX (No eXecute), can help prevent certain types of malicious code from exploiting a buffer overflow to get executed. Intel also released a series of Prescott supporting Intel 64, Intel's implementation of the AMD-developed x86-64 64-bit extensions to the x86 architecture. These were originally released as the F-series, and only sold to OEMs, but they were later renamed to the 5x1 series and sold to the general public. Two low-end Intel 64-enabled Prescotts, based on the 5x5/5x9 series, were also released with model numbers 506 and 516. 5x0, 5x0J, and 5x1 series Prescott incorporates Hyper-Threading in order to speed up some processes that use multithreaded software, such as video editing. The 5x1 series also supports 64 bit computing.

Prescott 2M (Extreme Edition)

Top view of a Pentium 4 Prescott 2M 640, 3.2 GHz

Bottom view of a Pentium 4 Prescott 2M 640

Intel, by the first quarter of 2005, released a new Prescott core with 6x0 numbering, codenamed "Prescott 2M". Prescott 2M is also sometimes known by the name of its Xeon derivative, "Irwindale". It features Intel 64, the XD Bit, EIST (Enhanced Intel SpeedStep Technology), Tm2 (for processors at 3.6 GHz and above), and 2 MB of L2 cache. However, higher cache latency and the double word size, if using Intel 64 mode, negated any advantage that added cache introduced. Rather than being a targeted speed boost the double size cache was intended to provide the same space and hence performance for 64-bit mode operations.

6xx series Prescott 2Ms have incorporated Hyper-Threading in order to speed up some processes that use multithreaded software, such as video editing.

On November 14, 2005, Intel released Prescott 2M processors with VT (Virtualization Technology, codenamed "Vanderpool") enabled. Intel only released two models of this Prescott 2M category: 662 and 672, running at 3.6 GHz and 3.8 GHz, respectively.

Cedar Mill

The final revision of the Pentium 4 was Cedar Mill, released on January 5, 2006. This was a die shrink of the Prescott-based 600 series core to 65 nm, with no real feature additions but significantly reduced power consumption. Cedar Mill had a lower heat output than Prescott, with a TDP of 86 W. The Core Stepping of D0 in late 2006 reduced this to 65 watts. It has a 65 nm core and features the same 31-stage pipeline as Prescott, 800 MT/s FSB, Intel 64, Hyper-Threading, but no Virtualization Technology. As with Prescott 2M, Cedar Mill also has a 2 MB L2 cache. It was released as Pentium 6x1 and 6x3 (product code 80552) at frequencies from 3 GHz up to 3.6 GHz. Overclockers managed to exceed 8 GHz with these processors using liquid nitrogen cooling.^[19]

To distinguish Cedar Mill cores from Prescott cores with the same features, Intel added 1 to their model numbers. Thus, Pentium 4 631, 641, 651 and 661 are 65 nm Cedar Mill microprocessors, while Pentium 630, 640, 650 and 660 respectively are their 90 nm Prescott equivalents.

The name "Cedar Mill" refers to Cedar Mill, Oregon, an unincorporated community near Intel's Hillsboro, Oregon facilities.

Successor

The original successor to the Pentium 4 was (codenamed) Tejas, which was scheduled for an early-mid-2005 release. However, it was cancelled a few months after the release of Prescott due to extremely high TDPs (a 2.8 GHz Tejas emitted 150 W of heat, compared to around 80 W for a Northwood of the same speed, and 100 W for a comparably clocked Prescott) and development on the NetBurst microarchitecture as a whole ceased, with the exception of the dual-core Pentium D and Pentium Extreme Edition and the Cedar Mill-based Pentium 4 HT.

Since May 2005, Intel has released dual-core processors based on the Pentium 4 under the names Pentium D and Pentium Extreme Edition. They represent Intel's shift towards parallelism and their intent was to eventually make the bulk of their main processor line multiple-core. These came under the code names Smithfield and Presler for the 90 nm and 65 nm parts respectively.

The ultimate successors to Pentium 4 are the Intel Core 2 processors using the "Conroe" core based upon the Core microarchitecture, released on July 27, 2006. Intel Core 2 processors have been released as single, dual and quad core processors. Single core counterparts are present in the Intel Core 2 line, primarily for the OEM market, while dual and quad core processors can be sold to retail and OEM.

See also

Notes and references

External links

• The future of Prescott: when Moore gives you lemons... at Ars Technica
• Prescott vs. Northwood Pentium 4 Review
• Intel Documentation
• Inside Pentium 4 Architecture
• The Microarchitecture of the Pentium 4 Processor
• P4 FPU's sensitive Denormalisation threshold and its effect on real-time audio processing