FM Synthesis Chips and Codec Chips

This article cannot possibly go into detail about the various primary chips used on PC sound cards, but to provide some summary as you explore, here is a synopsis of the FM synthesis chips and associated codecs and DACs and so on that were often employed on sound cards that were common during the DOS era. There is a lot more to a sound card than just these main chips which affect audio quality, but as the core component(s), they set the baseline for a card's capabilities.

FM Synthesis Chips

The FM synthesizer determines the number of independent sound "channels" (1=mono, 2=stereo, etc) that can be output at the same time, as well as the sounds that are played, their duration and effects (attack, sustain, decay, etc).

 

Yamaha YM3812

Yamaha created the YM3812 in 1985, a mono FM synthesis chip.

This is also known as "OPL2" as it was an incremental upgrade to the earlier Yamaha YM3526. It is pin-compatible with its forebear and uses the same serial DAC (digital-to-analog converter), but adds three additional waveforms.

YM3812 found widespread use because it was the chip used on the very popular Ad Lib sound card and since the Ad Lib became the de facto backward-compatible standard for PC audio, for many years the OPL2 chip enjoyed a life beyond its natural years. Due to its huge popularity, it was illegally cloned by other chip manufacturers.

YM3812 is an FM synthesizer chip which features 9 two-operator channels, OPL2 stands for "FM Operator Type L2". The "OPL2" (as it was called) was later used on the first Sound Blaster card, and two OPL2s were used on the early Sound Blaster Pro (for stereophonic sound) before being superceded by the OPL3 chip.

Click here for the YM3812 datasheet.

The YM3812 was also used on the following sound cards:

 

Yamaha YMF262, YMF289

Released in 1988, this is also known as "OPL3". An extended version of the original OPL2 chip (the YM3812), it basically had the capabilities of two YM3812 chips in one (it was designed as a replacement for the twin-OPL2 arrangement fitted to the earlier Creative Sound Blaster Pro cards). It adds an extra register base to provide a total of 18 two-operator channels. The first cards to use YMF262 were the Sound Blaster Pro 2 and Ad Lib Gold.

The YMF262 is capable of four-channel output using two of the YAC512 stereo signal DACs designed to accompany it, but most applications feature only two channels.

It was mostly sold in a 24-pin SOP package (see above) and provides an 8-bit parallel interface to the registers, requires a stable clock source of 14.318 MHz and one or two separate DACs (e.g. YAC512).

The YMF289 is a low-power version of the YMF262, so is also "OPL3". Used in laptops and PCMCIA sound cards, it was also used in some Sound Blaster 16 cards. Often paired with the YAC513 or YAC516 floating-point DAC (Digital-to-Analog Converter) chip.

Click here for the YMF262 datasheet, or here for the YMF289B datasheet.

 

Yamaha YMF715, YMF716, YMF718, YMF719

This is a later "OPL3" chip designed and made by Yamaha, called OPL3-SA, SA2 or SA3 - the SA, SA2 or SA3 refers to the generation of OPL3-SA chip, as these evolved over time, adding further functions on top of the previous generation. Within all of them though is a real embedded OPL3, which provides the card with a core of Ad Lib, Sound Blaster, Sound Blaster Pro, Windows Sound System and MPU-401 (UART) compatibility.

The original OPL3-SA provided plug & play compatibility. YMF701 chips are OPL3-SA (1st generation).

OPL3-SA2 added a CD-ROM interface, modem interface, a zoomed video port, and a DAC for OPL4. YMF711 and YMF718 are OPL3-SA2 (2nd generation)

OPL3-SA3 added a "3D sound" digital signal processor. YMF719 and higher are OPL3-SA3 chips (3rd generation).

There are several flavours of YMF719, including YMF719B-S and YMF719E-S. Windows 2000 and XP support this chipset out of the box (no external drivers). They are known for their low noise and excellent compatibility. Their MPU-401 interface does not suffer from the "hanging note" bug present in other OPL3 chips. For best quality the internal amp should be disabled via a jumper and all settings in the mixer set to 0 and setting the output type to hi-fi.

The YMF719 was the last Yamaha audio chip used on ISA sound cards. From YMF720 onwards they were all PCI-based.

Click here for the YMF715E datasheet (all the above mentioned chips are very similar to this).

 

Yamaha YMF720, YMF724

The YMF720 was the successor to the YMF719 OPL3-SAx. It has integrated OPL3 and semi-hardware General MIDI/DS-XG synth support with 2-channel output, as well as 3D audio via DirectSound3D and QSound.

The YMF724 was the code given to standalone PCI cards whereas YMF720 was for embedded systems (integrated directly on the motherboard).

Most boards with these chips have good quality 18-bit DACs, providing low noise and low harmonic distortion levels. The YMF724 includes a 64-voice wavetable synthesizer, interface to AC'97 codec, S/PDIF output and a Dolby AC-3 decoder.

These chips also include an OPL3 FM synthesizer, MPU-401 and Sound Blaster Pro support for backward compatibility. DOS applications running under Windows 9x and ME could also take advantage of the XG tone generator, available via Yamaha's VxD driver.

Click here for the YMF724 datasheet.

 

Yamaha YMF278

Also known as "OPL4". This chip is usually accompanied with a 2MB ROM (which holds approx. 330 samples) compatible with General MIDI. It incorporates both an FM synthesizer and a PCM sample-based synthesizer. The FM synthesizer is essentially a YMF262 (OPL3) so is also backwards-compatible with YM3526 (OPL) and YM3812 (OPL2), but can support 6 channels instead of 4. The PCM sample-based synthesis supports up to 24 simultaneous voices. It can access up to 4MB of external memory for wave data and a maximum of 512 samples.

Sound cards that use the YMF278 include:

Yamaha YMF740, YMF744, YMF754

An enhancement over the YMF720 and 724, the 740 and 744 provide 4-channel output instead of just 2. The YMF754 was a low-power version of the YMF744.

YMF740C Datasheet

ESS ESFM

An OPL3-compatible clone developed by ESS. It has 20 voices, 72 operators, and operates in two modes: Native and Legacy. In Native mode, ESFM allows more than six 4-operator FM voices to be mapped, potentially allowing for a significant increase in the complexity of tones generated. The drivers for Windows 9x incorporate their own custom instrument patches which make use of this extended mode. Conversely, Legacy mode provides full backward-compatibility with Yamaha's YMF262. ESFM's output in this mode is moderately faithful to the YMF262 overall, but some tones are rendered quite differently, resulting in unique distortions in the sound and music of some games. Sound cards that used ESFM were the ESS AudioDrive ES1688 and the ESS1938 Solo-1. Earlier boards typically used a Yamaha YMF262.

CRYSTAL CX4235

The CX4235 is a single-chip computer audio system that is pin-compatible to the CS423xB for many different designs. It includes an integrated FM synthesizer and plug-and-play interface. In addition, the CS4235 includes hardware master volume control pins as well as power management and 3D sound technology. The CS4235 is compatible with Sound Blaster, Sound Blaster Pro, and Microsoft Windows Sound System. The CS4235 is also fully compliant with Microsoft's PC 97 and PC 98 audio requirements.

Cards that used the CX4235 include:

  • Pine Technology PT-2318-20

OPTi 82C928 - MAD16

The OPTi MAD16 chipset is an integrated chip. Head over to the OPTi page for more details.

 

OPTi 82C929 - MAD16 Pro

The OPTi MAD16 Pro chipset is an integrated chip that supports Ad Lib, Sound Blaster, Sound Blaster Pro, Windows Sound System, and MPU-401 UART interface.

It can be found on the following sound cards:

 

OPTi 82C930

The OPTi 82C930 chipset is an integrated chip that supports Ad Lib, Sound Blaster, Sound Blaster Pro, Windows Sound System, and MPU-401 UART interface. Click here for the 83C930 Reference Guide.

 

OPTi 82C931

The OPTi 82C931 single-chip chipset was launched in 1996, and features Ad Lib, Sound Blaster, Sound Blaster Pro, and Windows Sound System compatibility. It supports 22 voice channels, 52 operators and employs OPTi's own OPTiFM(TM) music synthesizer with enhanced bass. It also has an MPU-401 interface common for this era. It's Plug & Play so expect cards that use this to all be PnP.

This OPTiFM OPL3 clone is reported to be "wonky" by user Ace on Vogons, citing "[the chip has] several incorrect notes and even volume spikes. Not recommended".

Cards that used the 82C931 include:

  • Unknown brand (FCC ID:E5X1817)

 

OPTi 82C933

The OPTi 82C933 single-chip chipset features Ad Lib, Sound Blaster, Sound Blaster Pro, and Windows Sound System compatibility. It supports 22 voice channels, 52 operators and employs OPTi's own OPTiFM(TM) music synthesizer with enhanced bass. It also has an MPU-401 interface common for this era. It's Plug & Play so expect cards that use this to all be PnP.

It also gets a built-in third-generation 16-bit Sigma-Delta codec by ECTIVA, which is further integrated with a low distortion complex mixer featuring 3-D audio expansion. The OPTiSound 82C933 produces a spatial or widened stereo image from ordinary left and right channel inputs, without any initial encoding of input signals.

As was typical for OPTi, these fully integrated chips found their way onto a number of nondescript sound cards such as this one.

82C933 Datasheet

 

OPTi 82C941

The OPTi 82C941 chip was a wavetable synthesizer, usually found paired on the higher-end 82C931 cards. The 931 portion delivered Ad Lib, Sound Blaster and Windows Sound System support, while the 941 wavetable effects (General MIDI). The wavetable needs no drivers to work - it's an MPU-401-compatible device, so responds to data received via the General MIDI address. According to an article on http://www.os2museum.com in order to get the wavetable working in pure DOS, you need to edit the SOUND16.CFG needs to be changed from FDAC_SRC=OPL3 to FDAC_SRC=SHARED.

 

COPIES (ILLEGITIMATE PERHAPS)

There also existed some chips which are believed to be full 100% copies of the original Yamaha chips. Some of the more common ones are the LS-212 and LS-215 pair of chips. The LS-212 is an YMF262-M OPL3 copy, while the LS-215 is a YAC512-M DAC equivalent. "215" is "512" backwards, probably not a coincidence. How do we know these are really copies? The OPTi 82C924 chipset does not include an OPL3-compatible core, yet boards that use this chipset claim to support OPL3, so the chip has to be there somewhere. So the LS-212/LS-215 pair is really the only suspect. Numerous Aztech cards got these copies.

There also exist less subtle chips blatently marked as LS262 (a copy of the YMF262 OPL3) and LS512 (a copy of the YAC512 DAC) and LS245 (a bus trasceiver).

Another set of clones are the DSP24S/DAP16S combination. These chips have been seen on a mid-1995 ProComp Pro-Multimedia cards next to an OPTi 82C929A controller. They appear to be straightforward copies of the YMF262-M and YAC512-M, respectively.

A third copy: FT6116 is a Force Technologies 2Kx8 CMOS SRAM. The FT6116-100 however, is… certainly not. Obviously a cheap Taiwanese sound card has no need for a fast SRAM (static RAM) chip. What’s more, the Avance Logic ALS100 does not include an OPL3 core (unlike its successor, the ALS100+), so an OPL3 chip has to be on the board somewhere. Yes, it's the FT6116-100 chip!

Last on the list is the DXP44Q. This chip appears to be a pin-compatible copy of the Yamaha YMF289B, also known as OPL3-L. This was a low-power chip with power management suitable for portables (and found in the ThinkPad 701C for instance). Once again, the OPTi 82C930A does not include an OPL3 core (unlike its successor, the 82C931). Once again, there has to be an OPL3 on the board somewhere, and the DXP44Q is more or less the only candidate. The 82C930A does include a DAC, which explains the lack of a separate DAC chip.

The fake OPL3 chips are most commonly, but by no means exclusively, found next to an OPTi controller. They have also been seen paired with ESS and Avance Logic controllers, and there’s no reason to think they couldn’t be used with others. The affinity with OPTi controllers could be simply a function of the fact that OPTi had well established and cost-effective controllers available in 1995. ESS and Crystal went relatively quickly from zero to integrating an OPL3 workalike (ESS1688, CS4235), obviating the need for external chips.

Audio Codecs

The job of the audio codec ("COder-DECoder") is to encode and decode a digital stream of data or signal, working in conjunction with the DAC (see further down this page). Below is some information on the more common codec chips found on PC sound cards.

Analog Devices (also known as ADI or SoundMax)

All their codec chips have the prefix "AD".

AD1815 Supports SB Pro and DirectSound.
MPU-401 MIDI port.
Integrated OPL3 clone.
Plug & Play.
16-bit input resolution.
55 kHz maximum sampling rate.

AD1815 Datasheet

AD1816 Supports SB Pro and Windows Sound System.
MPU-401 MIDI port.
Integrated OPL3 clone.
Plug & Play.
16-bit input resolution.
55 kHz maximum sampling rate.

Found on Highscreen Sound Boostar 16/32 3D (FCC ID: LWHA211A60)

AD1816JS Datasheet

AD1819B, 1881A, 1885, 1886A, 1887, 1981A, 1981B, 1981BL and 1981BW 2 channels.
16-bit input resolution.
48 kHz maximum input sampling rate
Signal-to-Noise ratio (SNR) range from 80-90 dB.
AD1981HD, 1983 2 channels.
20-bit input resolution.
24-bit output resolution.
48 kHz maximum sampling rate
Signal-to-Noise ratio (SNR) range from 80-85 dB.
AD1984 4 channels.
24-bit input resolution.
24-bit output resolution.
192 kHz maximum sampling rate
Signal-to-Noise ratio (SNR) range from 90-96 dB.
AD1985, 1986, 1986A 5.1 channels.
20-bit input resolution.
20-bit output resolution.
96 kHz maximum sampling rate
Signal-to-Noise ratio (SNR) range from 80-90 dB.
AD1882 5.1 channels.
24-bit input resolution.
24-bit output resolution.
96 kHz maximum sampling rate
Signal-to-Noise ratio (SNR) range from 90-95 dB.
AD1845 Supports Windows Sound System.
16-bit input resolution.
50 kHz maximum sampling rate. Pin-compatible with AD1848, AD1846, CS4248 and CS4231.


Found on Ensoniq SoundScape OPUS and Telesound PCA721AF (FCC ID: DXLSK81) sound cards.

AD1846 AD1846 Datasheet
AD1848 Supports Windows Sound System.
16-bit input resolution.
48 kHz maximum sampling rate.


Found on:

AD1848K Datasheet
AD1848KP Datasheet

AD1987, 1988A, 1988B 7.1 channels.
24-bit input resolution.
24-bit output resolution.
96 kHz (AD1987 only) maximum sampling rate. All others 192 kHz.
Signal-to-Noise ratio (SNR) range from 90-101 dB.

Realtek (also known as ALC or Avance Logic)

All their codec chips have the prefix "ALC". Click here for Avance Logic page.

ALC101, 202, 203, 250, 260 2 channels.
Input Resolution: ALC101 = 16-bit, ALC202/203/250 are 18-bit, ALC260 is 20-bit.
48 kHz maximum input sampling rate (ALC260 has 96 kHz)
48 kHz maximum output sampling rate on ALC101. 96 kHz on ALC202/203/250. 192 kHz on ALC260.
Signal-to-Noise ratio (SNR) is 70-75 dB on ALC101. All others range from 85-100 dB.
ALC262, 268, 269 4 channels.
20-bit input resolution (ALC269 is 24-bit)
24-bit output resolution.
96 kHz maximum input sampling rate.
192 kHz maximum output sampling rate.
Signal-to-Noise ratio (SNR) range from 80-85 dB.
ALC650, 655, 658, 662 5.1 channels.
Input resolution is 18-bit on ALC650 and 658, 16-bit on ALC655, and 20-bit on ALC662.
Output resolution is 20-bit on ALC650 and 658, 16-bit on ALC655, and 24-bit on ALC662.
48 kHz maximum input sampling rate on all but ALC662 which is 96 kHz.
Signal-to-Noise ratio (SNR) range from 85-98 dB.
ALC850, 861, 880 7.1 channels.
Input resolution is 16-bit on ALC850 and 861, 20-bit on ALC880, and 24-bit on ALC861-VD-GR.
24-bit output resolution on all but ALC850 which is 16-bit.
96 kHz maximum input sampling rate on all but ALC850 which is 48 kHz.
Signal-to-Noise ratio (SNR) range from 82-100 dB.

CRYSTAL (cirrus logic's low-end audio codec brand)

Cirrus Logic, Inc. produced some of the highest quality audio codecs, mainly used in home theatre receivers. In 1991 they acquired Crystal Semiconductor, a supplier of analog and mixed-signal converter ICs. The Crystal codecs were then marketed as Cirrus Logic's budget line. All these codec chips have the prefix "CS".

CS4231-KL, CS4231A-KL

Introduced in 1994, the CS4231 had 16-bit audio converters, analog mixing, supported Ad Lib, Sound Blaster and Windows Sound System (WSS) compatibility. (*NO* SB Pro).

The CS4231A is a pin-compatible upgrade to the CS4231 and CS4248, and is fully backward-compatible with those forebears.

Found on:

Datasheets: CS4231, CS4231A,
Drivers

CS4232

Crystal's first plug & play codec, CS4232, arrived in early 1995. It had no integrated FM chip so most cards that use the CS4232 would also have an OPL3 or compatible chip.
Sound Blaster, Sound Blaster Pro (Stereo) and WSS 2.0 compatible.
Up to 16-bit 48 kHz full duplex hardware compression.

Requires DOS initialisation for the MPU-401 to work in Windows.

Found on:

  • Acer Magic S32/S23 (S23 uses Crystal CS4232, S32 uses Creative's Vibra-16S chipset)
  • Terratec Maestro 32/96 
  • Reveal SC500 Rev. 3
  • CrystaLake Multimedia 120 (1 MB)
  • CrystaLake Multimedia 140 (4 MB)
  • Ad Lib ASB4

Click here for the CS4232 datasheet

Drivers

It is usually recommended that you use the installation software from your sound card's manufacturer, but in the absence of those, try one of these:
Windows 3.x
Windows NT 3.51 and 4.0
Windows 95
OS/2

 

CS4235 / CS4239

The CS4235 is a low-cost version of the CS4236B, introduced in late 1997.
Supports full duplex.
Is Plug & Play.
Features FM synthesis on-chip.
Supports Mode 3.
Sound Blaster / SB Pro / WSS compatible.

Apparently the CS4235 got a very glitchy OPL3 FM synthesizer, so best to avoid cards or motherboards that have this chip.

A low-power version of the CS4235 was also released, called CS4239.

Click here for the CS4235 datasheet
DOS Drivers

CS4236

Introduced in 1997, the CS4236 was fully compliant with the Microsoft PC '97 and WHQL (Windows Hardware Quality Labs) audio requirements.
Supports full duplex.
Is Plug & Play.
Features an FM synthesis on-chip.
Supports Mode 3.
Sound Blaster Pro compatible.

CS4236 has low noise, does not suffer from the hanging note bug on the MPU-401 interface and decent compatibility with Sound Blaster, SB Pro and Windows Sound System.

Requires DOS initialisation for the MPU-401 to work in Windows.

Found on:

Click here for the CS4236 datasheet

Drivers

It is usually recommended that you use the installation software from your sound card's manufacturer, but in the absence of those, try one of these:
Windows 3.x
Windows NT 3.51 and 4.0
Windows 95
OS/2


CS4236B

CS4236B and higher are Mode 3 devices. Does not require DOS initialisation for the MPU-401 to work in Windows. This revision B chip also has a "wavetable digital interface".

Found on Intel SE440BX motherboard (1998). Also found on the Terratec EWS64L and XL cards.

CS4237

The same chip as CS4236B but with SRS surround sound (by SRS Labs).

Click here for the CS4237B datasheet.

Found on Kentech KJD-MUSIC16, SB3202 and AOpen card (FCC ID: IPLAW35)

 

Drivers

It is usually recommended that you use the installation software from your sound card's manufacturer, but in the absence of those, try one of these:
DOS
Windows 3.x
OS/2

 

CS4238

The same as CS4237 but has QSOUND surround sound (from QSound, Inc.) instead of SRS.

Drivers

It is usually recommended that you use the installation software from your sound card's manufacturer, but in the absence of those, try one of these:
Windows 3.x
OS/2

 

CS4248

One of Crystal's first audio codecs for sound cards, introduced in 1993.
16-bit input resolution.
Not full duplex.
Up to 50 kHz maximum input sampling rate.
This is a clone of Windows Sound System.
Found on:

Click here for a CS4248 datasheet.

CS4280, CS4281

Arriving in 1998, CS4280 and CS4281 are PCI audio chips.

CS4280 is found on the JoyTech Twister 3D sound card.

Datasheets: CS4280, CS4281.

CS4297 This AC'97 audio chip is a simple codec that is supposed to be paired with something like a CS4610.
CS4611 An embedded audio chip found on the Intel SE440BX motherboard from 1998 alongside the CS4236.
CS4614 A PCI audio chip.
CS9233 / CS9236

A wavetable synthesis chip with reverb and chorus, so supports GM (General MIDI). No DAC. Requires DOS initialisation for the MPU-401 to work in Windows.

Its ROM soundfont is typical of old 1 and 2 MB ROMs. The CS9236 supports reverb and chorus effects.

 

DACs

DACs (Digital- to Analog- Converters) are used in almost all sound cards, since the main FM synthesizer chip outputs its audio in digital form. The DAC converts these digital I/O signals into analog signals ready for your sound card to mix it or send it straight out to your loudspeakers.

Windows Sound System v1.0 tended to use the AD1848 DAC. The later WSS 2.0 used Crystal CS4231.

 

YAC512

The Yamaha YAC512 was designed to work alongside the YMF262 or YMF289 FM synthesizer chip.

Click here for the YAC512 datasheet.

 

YAC513 / YAC516

The Yamaha YAC513 was typically paired to the low-power version of the YMF262, the YMF289.

Click here for the YAC513 datasheet or here for the YAC516 one.

 

 

Embedded Sound Chips on Motherboards

In the late 1990s, motherboard manufacturers began embedding audio chips, effectively entire sound card technology, on their boards. Whilst these were convenient as PC builders no longer had to install a separate sound card and use up another free slot, the audio quality was often very poor. This section lists the most common of these embedded sound chips.

For C-Media sound drivers, visit their website here.

C-Media ASC-9308

Compatible with Sound Blaster and Sound Blaster Pro (Still named "Compumedia", also gives nearly useless SB16 compatibility).

C-Media CMI8328

Has an MPU-401 (UART only) interface.

C-Media CMI8330

Often found on cheap PC Chips motherboards, these are sometimes branded "HT1869V+ SoundPro". Also found on some ASUS motherboards. Rarely used on sound cards.
Compatible with Sound Blaster, SB Pro, SB16, WSS, and has an MPU-401 (UART only) interface,
OPL3 clone integrated. Even though the chip has "PCI" written on it, it actually uses the ISA bus.
Plug & Play.
S/PDIF input/output.

One rare example of a card with this chip is this one from Elpina. There are other versions of this same card that are unbranded, but are identical in every other way. The card's DOS compatibility is supposedly very good though FM output is incredibly quiet (low volume) and the card is susceptible to picking up lots of noise.

Drivers

It is usually recommended that you use the installation software from your sound card's manufacturer, but in the absence of those, try one of these:
DOS, Windows 3.1, Windows 95
Windows 95 Driver update DirectX v5.0
Updated Mixer program v1.7A
Driver Update to Fix Windows 98 Problems

 

C-Media CMI8338

Often found on cheap PC Chips motherboards, although are sometimes branded "HT8338/PCI SoundPro".

C-Media CMI8738

Often found on cheap PC Chips motherboards, although are sometimes branded "HT8738/PCI SoundPro". This was the same as the CMI8338, but included an integrated PCtel 56K PCI fax/modem. It's also found on many cheap PCI sound cards.

Realtek

Realtek embedded sound chips post-date the DOS era, so won't be covered here.

YAMAHA OPL3-SAx

It is usually recommended that you use the installation software from your sound card's manufacturer, but in the absence of those, try one of these:

DOS
Windows 3.x
Windows 95
Windows NT 3.51/4.0
OS/2