oss_envy24: Ice envy24 audio device driver.

DESCRIPTION

Open Sound System driver for Envy24 based audio cards such as the M-Audio Delta Series, Terratec EWS88 Series, Hoontech DSP24.

 ENVY24 device characteristics:

8/16 bit playback/record
mono/stereo/4ch/5.1ch/7.1ch playback
mono/sterero recording
8KHz to 192Khz sample rate.

 ENVY24 AUDIO DEVICES

        Audio devices:
        0: M Audio Delta 1010 out1/2
        1: M Audio Delta 1010 out3/4
        2: M Audio Delta 1010 out5/6
        3: M Audio Delta 1010 out7/8
        4: M Audio Delta 1010 S/PDIF out
        5: M Audio Delta 1010 in1/2
        6: M Audio Delta 1010 in3/4
        7: M Audio Delta 1010 in5/6
        8: M Audio Delta 1010 in7/8
        9: M Audio Delta 1010 S/PDIF in
        10: M Audio Delta 1010 input from mon. mixer
        11: M Audio Delta 1010 (all outputs)
        12: M Audio Delta 1010 (all inputs)

        Synth devices:

        Midi devices:
        0: M Audio Delta 1010

        Timers:
        0: System clock

        Mixers:
        0: M Audio Delta 1010

The actual /dev/dsp# numbers may be different on your system. Check the right ones by looking at the output procuced by "ossinfo -a" command. With the above configuration you can use /dev/dsp0 to /dev/dsp4 for playback of stereo streams. If you play mono files the signal will be output only from the left channel. /dev/dsp0 to /dev/dsp3 are connected to the analog outputs while /dev/dsp4 is the S/PDIF output.

The /dev/dsp5 to /dev/dsp10 device files can be used for recording. /dev/dsp5 to /dev/dsp8 are the analog inputs. /dev/dsp11 and /dev/dsp12 are raw input/output device files. They will be described in detail in the "Raw I/O devices" section below.

It's also possible to make OSS to create individual device files for every channel this creates twice as many device files than the default setting. To do this just append envy24_skipdevs=1 to the oss_envy24.conf file. This is useful only if you are working on mono rather than stereo signals. However please note that setting envy24_skipdevs=1 does _NOT_ lock the device files to one channel mode, the application can still set them to stereo or multi channel mode if it likes.

It is possible to set all device files to mono only mode by setting envy24_skipdevs=1 and envy24_force_mono=1. However this mode disables stereo and multi channel usage for all devices so in general it should not be used.

By default the driver will create output devices before the input ones. By setting envy24_swapdevs=1 in oss_envy24.conf you can ask OSS to create the device files in opposite order i.e. input device files before the output ones. This may be useful when using RealProducer.

As a workaround to a bug in RealProducer you also need to create some dummy mixer devices by defining envy24_realencoder_hack=1 in oss_envy24.conf. Without these extra mixer devices RealProducer will not be able to access other than the first input device.

DEVICE MANAGEMENT

By default OSS creates a large number of device files for each envy24 card. This may be a problem when multiple cards need to be used in the same system. Adding the envy24_devmask option to oss_envy24.conf should help in most cases because it removes the devices that are actually not needed in the system.

The envy24_devmask number is the SUM of the following values:

        1: Create primary (analog/ADAT/TDIF) outputs.
        2: Create primary (analog/ADAT/TDIF) inputs.
        4: Create S/PDIF outputs.
        8: Create S/PDIF inputs.
        16: Create monitor input device.
        32: Create the raw input and output devices.

For example envy24_devmask=12 (4+8) creates only the S/PDIF devices. To enable all possible (current or future) device files set envy24_devmask to 65535 (default).

If possible make your application to open the right device file (/dev/dsp0 to /dev/dsp10) explicitly. It's also possible to use the default devicefile (/dev/dsp) since OSS now supports automatic device allocation (it opens the first available input or output devicefile depending on the open mode).

The channel allocation mechanism between device files is very flexible. Even there is a device file for every stereo pair (or a mono channel) it's possible to use any of the device file to access multiple channels. For example an application can open /dev/dsp0 and set the number of channels to 10. In this way the application can play all 10 channels (or any number between 1 and 10) simultaneously (the samples will be interleaved).

There is simple automatic syncstart feature when using multiple applications at the same time. Playback will not start before all currently open devices files have started the playback operation. The same mechanism works for recording (recording and playback operations are fully independent).

The Envy24 driver supports 8, 16 and 24/32 bit sample formats.

SAMPLING RATE

Envy24 based cards are multi channel devices and all the channels share the same sampling rate. For this reason the sampling rate is normally locked to the value selected using ossmix. However OSS supports some other methods for changing the sampling rate. There are four ways to change the sampling rate.

  BASIC METHOD:

Since all input and output channels of Envy24 work at the same sampling rate it's not possible for the applications to select the rate themselves. Instead the sampling rate is always locked to the currently selected rate. This rate selection can be changed using the ossmix program shipped with OSS.

For example:

        ossmix envy24.rate 48000

sets the sampling rate to 48000 Hz (default). The possible alternatives are

8000
9600
11025
12000
16000
22050
24000
32000
44100
48000
88200
96000

When using S/PDIF inputs/outputs only the sampling rates 32000, 44100, 48000, 88200 or 96000 should be used.

EXTERNAL SYNC

It's possible to lock the sampling rate to the S/PDIF or world clock inputs by setting the envy24.sync setting in ossmix to SPDIF or WCLOCK. However the envy24.rate setting should be set manually to match the rate being used (there is no autodetection for that).

NONLOCKED METHOD

It's also possible to turn the envy24.ratelock setting to OFF using ossmix. After that the first application that opens the device can change the sampling rate. However great care should be taken that this application gets the recording/playback process fully started before any of the other applications open their devices. Otherwise all devices will be locked to 8Khz. Also keep in mind that subsequent applications will be forced to use the sampling rate set by the first one.

SOFTWARE SRC

OSS contains a very high quality software based sample rate converter. It can be enabled by setting envy24.src to ON using ossmix.

After that OSS can do on-fly sample rate conversions between the actual "hardware" sampling rate and the sampling rates used by the applications. In this way every application may use different sampling rate. However there are some drawbacks in this method:

The hardware rate needs to be 44100, 48000 or 96000 Hz.
The software SRC algorithm consumes some CPU time (1% to 20% per audio channel depending on the CPU speed and sampling rates). For this reason this method may be useless in multi channel use with anything else but the fastest high end CPUs.
Only mono and stereo (1 or 2 channel) streams are supported.
The SRC algorithm does cause minor artifacts to the sound (SNR is around 60 dB).

RAW IO DEVICES

These device files provide an alternative way to access Envy24 based devices. With these devices it's possible to bypass the dual buffering required by the "normal" input-output device files described above. This means that also the mmap() feature is available and that the latencies caused by dual buffering are gone. So these device files work much like "ordinary" soundcards. However due to multi channel professional nature of the Envy24 chip there are some very fundamental differences. This means that these device files can only be used with applications that are aware of them.

The differences from normal audio device files are:

1.: The sample format will always be 32 bit msb aligned (AFMT_S32_LE). Trying to use any other sample format will cause unexpected results.
2.: Number of channels is fixed and cannot be changed. The output device has always 10 channels (0 to 7 are analog outputs and 8 to 9 are the digital outputs). This assignment will be used even with cards that don't support digital (or analog) outputs at all. If the actual hardware being used has less channels the unused ones will be discarded (however they will be fed to the on board monitor mixer).

The input device is fixed to 12 channels. Channels 0 to 7 are analog inputs. Channels 8 to 9 are digital inputs. Channels 10 and 11 are for the result signal from the on board monitor mixer.

DIGITAL MONITOR MIXER

All Envy24 based cards have a built in monitor mixer. It can be used to mix allinput and output signals together. The result can be recorded from the "input from mon mixer" device (device 10 in the /dev/sndstat example above). The monitor mix signal can also be routed to any of the outputs (including S/PDIF and the "consumer" AC97 output of Terratec EWS88MT/D and any other card that support s it).

The settings in the gain.* group of ossmix are used to change the levels of all inputs and outputs in the digital monitor mixer. The possible values are between 0 (minimum) and 144 (maximum).

OSS permits using all 10 possible output channels of the monitor mixer even with cards that have less physical outputs. These "virtual" outputs are only sent to the monitor mixer and their signal is only present in the monitor mixer output. To enable these "virtual" channels set the envy24_virtualout parameter to 1 in oss_envy24.conf. This option has no effect with Delta1010, EWS88MT and other cards that have 10 "real" outputs.

SYNC SOURCE

On cards with S/PDIF and/or World Clock inputs it's possible to select the sync source using

        ossmix envy24.sync

The possible choices are:

INTERNAL: Use the internal sampling rate as defined by envy24.rate
SPDIF: Use the S/PDIF input as the clock source. The envy24.rate setting must be set manually to match the actual input sampling rate.
WCLOCK: Like SPDIF but uses the world clock input signal (Delta 1010 only).

OUTPUT ROUTINGS

Output routing of output ports can be changed by changing the route.* settings using ossmix. The possible choices are:

DMA: Playback from the associated /dev/dsp# device.
MONITOR: Output of the digital mixer (only out1/2 and S/PDIF).
IN1/2 to IN9/10 or IN1 to IN10: Loopback from the analog inputs
SPDIFL or SPDIFR or SPDIF: Loopback from the S/PDIF input.

PEAK METERS

Envy24 based cards have peak meters for the input and output ports of the digital monitor mixer. ossmix can show these values under the peak.* group (these settings are read only). The values are between 0 (minimum) and 255 (maximum). At this moment the only applications that supports these peak meters are ossmix and ossxmix.

AUDIO LATENCY

IDE disk and CD-ROM drives may cause some interrupt latency problems which may cause dropouts in recording/playback with Envy24 based cards. For this reason ensure that DMA is turned on for the disk drive.

Another method to solve the dropout problems is making the fragment size used by the driver longer. This can be done by adding envy24_nfrags=N to the oss_envy24.conf file. By default N is 16. Values 2, 4 or 8 make the fragments longer which should cure the dropout problems. However this may cause latency problems with some applications. Values 32 and 64 decrease the latencies but may cause dropouts with IDE.

oss_envy24 (7)