---
name: "snd_hdsp"
section: "4"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/snd_hdsp"
---

# snd\_hdsp(4)

RME HDSP bridge device driver

## NAME

**snd\_hdsp** – RME HDSP bridge device driver

## SYNOPSIS

To compile this driver into the kernel, place the following lines in your kernel configuration file:

**device sound** **device snd\_hdsp**

Alternatively, to load the driver as a module at boot time, place the following line in [loader.conf(5)](/loader.conf/5.md):

```
snd_hdsp_load="YES"
```

## DESCRIPTION

The **snd\_hdsp** bridge driver allows the generic audio driver [sound(4)](/sound/4.md) to attach to RME HDSP audio devices.

## HARDWARE

The **snd\_hdsp** driver supports the following audio devices:

- RME HDSP 9632 (optional AO4S-192 and AIS-192 extension boards)

- RME HDSP 9652

By default, each [pcm(4)](/pcm/4.md) device corresponds to a physical port on the sound card. For ADAT ports, 8 channel, 4 channel and 2 channel formats are supported. The effective number of ADAT channels is 8 channels at single speed (32kHz-48kHz) and 4 channels at double speed (64kHz-96kHz). Only the HDSP 9632 can operate at quad speed (128kHz-192kHz), ADAT is disabled in this mode. Depending on sample rate and channel format selected, not all pcm channels can be mapped to ADAT channels and vice versa.

## LOADER TUNABLES

These settings can be entered at the [loader(8)](/loader/8.md) prompt or in [loader.conf(5)](/loader.conf/5.md).

- *hw.hdsp.unified\_pcm*

  If set to 1, all physical ports are combined into one unified pcm device. When opened in multi-channel audio software, this makes all ports available at the same time, and fully synchronized. For resulting channel numbers consult the following table:

| | | | |
| --- | --- | --- | --- |
|  | Play \| Rec | Play \| Rec | Play \| Rec |
| HDSP 9632 | 16 \| 16 | 12 \| 12 | 8 \| 8 |
| HDSP 9652 | 26 \| 26 | 14 \| 14 | - \| - |

**Sound Card** 	 **Single Speed** 	 **Double Speed** 	 **Quad Speed**

## SYSCTL TUNABLES

These settings and informational values can be accessed at runtime with the [sysctl(8)](/sysctl/8.md) command. If multiple RME HDSP sound cards are installed, each device has a separate configuration. To adjust the following sysctl identifiers for a specific sound card, insert the respective device number in place of ‘0’.

- *dev.hdsp.0.sample\_rate*

  Set a fixed sample rate from 32000, 44100, 48000, up to 192000. This is usually required for digital connections (AES, S/PDIF, ADAT). The default value of 0 adjusts the sample rate according to pcm device settings.

- *dev.hdsp.0.period*

  The number of samples processed per interrupt, from 32, 64, 128, up to 4096. Setting a lower value here results in less latency, but increases system load due to frequent interrupt processing. Extreme values may cause audio gaps and glitches.

- *dev.hdsp.0.clock\_list*

  Lists possible clock sources to sync with, depending on the hardware model. This includes internal and external master clocks as well as incoming digital audio signals like AES, S/PDIF and ADAT.

- *dev.hdsp.0.clock\_preference*

  Select a preferred clock source from the clock list. HDSP cards will sync to this clock source when available, but fall back to auto-sync with any other digital clock signal they receive. Set this to ‘internal’ if the HDSP card should act as master clock.

- *dev.hdsp.0.clock\_source*

  Shows the actual clock source in use (read only). This differs from what is set as clock preference when in auto-sync mode.

- *dev.hdsp.0.sync\_status*

  Display the current sync status of all external clock sources. Status indications are ‘none’ for no signal at all, ‘lock’ for when a valid signal is present, and ‘sync’ for accurately synchronized signals (required for recording digital audio).

The following tunables are applicable to HDSP 9632 devices only:

- *dev.hdsp.0.input\_level*

  Select the sensitivity of the analog line input. Available reference levels for the input signal are ‘LowGain’, ‘+4dBu’ and ‘-10dBV’.

- *dev.hdsp.0.output\_level*

  Select the gain level of the analog line output. Available reference levels for the output signal are ‘HighGain’, ‘+4dBu’ and ‘-10dBV’.

- *dev.hdsp.0.phones\_level*

  Adjust the gain level of the phones output, separately from the analog line output. The signal can be lowered by 6 or 12 dB.

Where appropriate these sysctl values are modeled after official RME software on other platforms, and adopt their terminology. Consult the RME user manuals for additional information.

## SEE ALSO

[sound(4)](/sound/4.md)

## HISTORY

The **snd\_hdsp** device driver first appeared in FreeBSD 15.0.

## AUTHORS

Based on [snd\_hdspe(4)](/snd_hdspe/4.md) originally written by Ruslan Bukin \<br@bsdpad.com\>. All adaptation to HDSP cards by Florian Walpen \<dev@submerge.ch\>.